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Terminal Listings

Each terminal will be dealt with individually to show more clearly its role in the overall installation. Table 3 lists the ECM terminal connections, and then each terminal is examined individually.

Table 3 - ECM Connector Table 
ECM
Wire Color
Circuit Number
Description
a-1
DARK GREEN/WHITE
Circuit #465
FUEL PUMP RELAY CONTROL
a-2
BROWN
Circuit #436
AIR SWITCH (PORT SOLENOID)
a-3
DARK GREEN/YELLOW
Circuit #428
CANISTER PURGE CONTROL
a-4
GRAY
Circuit #435
EGR SOLENOID CONTROL
a-5
BROWN/WHITE
Circuit #419
CHECK ENGINE/SERVICE ENGINE SOON LIGHT CONTROL
a-6
PINK/BLACK
Circuit #439
+12V IGNITION supply
a-7
TAN/BLACK
Circuit #422
Automatic Trans TCC CONTROL
   
Circuit #422
Manual Transmission O-D CONTROL
   
Circuit #456
Manual Transmission SHIFT LIGHT CONTROL
a-8
ORANGE
Circuit #461
SERIAL DATA
a-9
WHITE/BLACK
Circuit #451
DIAGNOSTIC TERMINAL
a-10
BROWN
Circuit #437
VSS SIGNAL
a-11
BLACK/pink
Circuit #476
ANALOG GROUND (+5V Return)
a-12
BLACK/WHITE
Circuit #450
SYSTEM GROUND
b-1
ORANGE
Circuit #340
+12V BATTERY supply
b-2
TAN/WHITE or RED
Circuit #120
FUEL PUMP SIGNAL
b-3
BLACK/RED
Circuit #453
EST REFERENCE
b-4
   
not used
b-5
PURPLE/WHITE
Circuit #430
DISTRIBUTOR REFERENCE
b-6
WHITE, PURPLE or DARK BLUE
Circuit #963
VATS (Pass-Key)
b-7
BLACK
Circuit #485
ESC SIGNAL
b-8
GREEN or GREEN/YELLOW
CIRCUIT #59
A/C SIGNAL
b-9
   
not used
b-10
ORANGE/BLACK
Circuit #434
PARK / NEUTRAL SIGNAL
b-11
   
not used
b-12
DARK GREEN
Circuit #998
MAF INPUT
c-1
DARK GREEN /WHITE
Circuit#335
FAN RELAY CONTROL
c-2
BLACK/pink
circuit #429
AIR SWITCH (DIVERT SOLENOID)
c-3
IAC lt green/black
Circuit #444
iac coil B LO
c-4
IAC Lt green/white
Circuit #443
iac coil B Hi
c-5
IAC lt blue/white
Circuit #441
iac coil A Hl
c-6
IAC lt blue/black
Circuit #442
iac coil A LO
c-7
BLACK/BLUE
Circuit #925
A/T O-D SWITCH SIGNAL
c-8
black/lt blue
Circuit #905
M/T O-D REQUEST
c-8
DARK GREEN or LT.BLUE
Circuit #446
A/T O-D 4TH GEAR
c-8
BLACK/BLUE or LIGHT BLUE
Circuit#902
M/T O-D REQUEST (4SPD Man w/OD)
c-9
   
not used
c-10
YELLOW
Circuit #410
COOLANT TEMPERATURE SIGNAL
c-11
   
not used
c-12
TAN
Circuit #472
MAT SIGNAL
c-13
DARK BLUE
Circuit #417
TPS SIGNAL
c-14
GRAY
Circuit #416
TPS +5V REFERENCE
c-15
DARK GREEN
Circuit #935
EGR DIAGNOSTIC SWITCH
c-16
ORANGE
Circuit #340
+12V BATTERY supply
d-1
BLACK/WHITE
Circuit#450
SYSTEM GROUND
d-2
BLACK
Circuit #452
TPS, CTS, MAT +5v RETURN
d-3
BLACK/WHITE
Circuit #450
SYSTEM GROUND
d-4
WHITE
Circuit #423
EST CONTROL
d-5
TAN/BLACK
Circuit#424
BYPASS
d-6
TAN
Circuit #413
OXYGEN SENSOR GROUND
d-7
PURPLE
Circuit#412
OXYGEN SENSOR SIGNAL
d-8
   
not used
d-9
   
not used
d-10
BLACK/WHITE
Circuit #450
SYSTEM GROUND
d-11
DARK BLUE
Circuit #732 or
A/C PRESSURE
 
DARK GREEN
Circuit #992 or
FAN SWITCH
 
GRAY
Circuit #731
(colour code and circuit # vary with different vehicles.)
d-12
BLACK
Circuit #900
MAF BURN-OFF RELAY CONTROL
d-13
   
not used
d-14
   
not used
d-15
LIGHT BLUE or BLACK/PINK
Circuit #467
INJ 1-3-5-7
d-16
LIGHT GREEN or BLACK/GREEN
Circuit #468
INJ 2-46-8

ECM Terminal Descriptions

Each ECM Terminal is dealt with in the following text. Those terminals not in use are not shown here. Where necessary, reference is made to specific year/models and differences between wiring harnesses are indicated. Every attempt has been made to cover all models, but factory alterations, accessory installations and customizing techniques may cause different wiring source and destination locations than that which appears here. Always check carefully any ambiguous differences.

A-1
Circuit #465
FUEL PUMP RELAY CONTROL

Connected to Terminal C (Design 1) or D (Design 2) of the fuel pump relay.

This circuit allows the ECM to activate the fuel pump relay by supplying a +12V through this terminal. The fuel pump power circuit is provided by a connection to relay Terminal E (Design 1) or A (Design 2) of the +12V (Circuit #340) wire directly from the Battery Fuse (Fuse #1). In addition, Terminal B (Design 1) or F (Design 2) of the fuel pump relay should be connected to the common ganged ground circuit from ECM connector Terminals A-12, D-1, D-3, D-6, and D-10 which is, in turn, connected to a secure engine ground. A wire should be connected from the fuel pump relay Terminal A (Design 1) or E (Design 2), to the fuel pump positive terminal, and also to ECM Terminal B-2 (Circuit #120). This connection to the fuel pump from Terminal A or E is, in turn, powered to run the pump, when the ECM connection at A-1 is powered, to activate the relay. The connection at B-2 provides an input to the ECM to acknowledge that the pump has power. A wire should also be connected from Terminal D (Design 1) or C (Design 2) of the fuel pump relay, to Terminal G of the ALDL connector. This connection will allow you to power up the fuel pump by supplying +12V to this terminal of the ALDL connector for test purposes.

A-2
Circuit#436
AIR SWITCH (PORT SOLENOID)

Connected to the Port Solenoid Connector (Gray) of the AIR valve.

This circuit allows the ECM to activate the port solenoid portion of the AIR valve assembly by supplying a ground through this terminal. The +12V supply to this connector is supplied from a fused, switched source, via the gauges fuse in the original application. For our rewiring purposes, we shall refer to this fuse circuit as Fuse #3 and Circuit #39. If the AIR system is retained with the installation, a wire should also be connected from this terminal to Terminal C of the ALDL connector to duplicate the factory hookup. This ALDL connection will allow you to activate the Port Solenoid, by jumpering ALDL terminal C to ground for diagnostic purposes. As mentioned earlier in this manual, while the ECM controls this circuit, it does not monitor it, so the AIR system and this circuit can be eliminated with no negative effects on ECM operation or diagnostics.

DELETE if removing AIR pump and valve assembly.
A-3
Circuit #428
CANISTER PURGE CONTROL

Connected to Emission Canister Purge control connector (Red) Terminal B.

This circuit allows the ECM to activate the CCP (Controlled Canister Purge) evaporative emission canister purge control solenoid by providing a ground through this terminal. If this circuit is used, the +12V supply portion is derived from the same (gauges) Fuse #3 Circuit #39 referred to as the +12V supply source for the AIR port solenoid as indicated in Para 65. Here again, while the ECM controls this circuit, it does not monitor the action of the CCP system so this system, and its circuit, can be removed without affecting ECM operation or diagnostics.

DELETE if not using evaporative emission canister.
A-4
Circuit #435
EGR SOLENOID CONTROL

Connected to the EGR Control Solenoid connector Terminal B.

This circuit allows the ECM to control the operation of the EGR solenoid by providing a ground through this terminal. When the EGR solenoid is activated, or turned ON by this process, it closes the vacuum passage to the EGR valve, thus making it inoperative, supplying no EGR to the engine. Conversely, when the ground is removed from this terminal, it turns the EGR solenoid OFF. This opens the vacuum passage to the EGR valve which, in turn, opens the valve and allows the EGR function to the engine. When the EGR function is commanded by the ECM, this ON-OFF process takes place many times a second in what is referred to as a pulse-width-modulated duty cycle. The EGR solenoid is powered by gauges Fuse #3, Circuit #39. If you are removing the EGR system, this circuit can be deleted if the park/neutral switch connector (B-10 ) is connected to the ganged common ground wire circuit connected to ECM terminals A-12, D-1, D-3 D-6, and D-10. When Terminal B-10 is grounded in this manner, it effectively defeats the EGR systems self-diagnostics and therefore does not allow the ECM to illuminate the Check Engine/ Service Engine Soon light or set a trouble code to indicate a problem with the EGR system. For more information see Para 98, 99.

DELETE if removing EGR valve and control solenoid.
A-5
Circuit #419
CHECK ENGINE/SERVICE ENGINE SOON LIGHT CONTROL

Connected to the Check Engine/Service Engine Soon light.

This circuit allows the ECM to provide a ground to the Check Engine/Service Engine Soon Light, thus illuminating the light to alert the driver to possible problems with the ECM, individual sensors or wiring. Power for this light should be provided from the gauges fuse (Fuse #3-Circuit #39). WE STRONGLY RECOMMEND THE INCLUSION OF THIS CIRCUIT in the re-wiring process as this light is an important part of the systems self-diagnostics. For more information on the Check Engine/Service Engine Soon light, refer Page 6, Trouble Codes.

A-6
Circuit #439
+12V IGNITION circuit

Connected to a switched +12V source.

This circuit provides power to the ECM from a +12V switched source (the ignition switch) fused by a 10 amp fuse. Power should be available at this terminal when the ignition key is in the run and start positions. Depending on the type of wiring system that exists in the vehicle into which you are installing the TPI system, you will have to either tap into the appropriate wire in the ignition switch harness, or make the necessary connection at the main fuse block. For our rewiring purposes, this fuse will be referred to as the ECM fuse (or Fuse #2). In the factory hook-up, circuit #439, which provides power from Fuse #2 to this terminal, also provides power to the ESC module Terminal B and, in vehicles equipped with a VATS decoder module, to Terminal A-1 or S (depending on year and model) of that module. When we rework the wiring loom for the Non-OEM installation, we power the ESC module from the gauges fuse (Fuse #3-Circuit #39 ). This effectively makes the ECM the only component supplied with power from Fuse #2.

A-7
Circuit #422
Automatic Trans TCC CONTROL
 
Circuit #422
Manual Transmission O-D CONTROL
 
Circuit #456
Manual Transmission SHIFT LIGHT CONTROL

refers. Connected to the TH-700-R4 automatic transmission TCC Solenoid (Terminal D).

This circuit allows the ECM to control the TCC function by providing a ground through this terminal. We DO NOT recommend using the ECM to activate the TCC function in the OEM manner because this requires the inclusion of a functional VSS system. A much simpler solution is to use one of the many after-market kits available to effect TCC lockup without the use of a computer. Our method of accomplishing this is detailed later in this manual. Refer Part Nine, Miscellaneous Information (Page 43 Para 13).

If you ARE using the ECM to activate the TCC function, a wire should be connected from this terminal to the ALDL connector (Terminal F Figure 10 ). This connection allows you to activate the TCC function by supplying an external ground to this ALDL terminal to verify TCC operation. On Corvettes equipped with a manual 4-speed plus overdrive transmission, this terminal allows the ECM to provide a ground to the overdrive relay which in turn, activates the overdrive solenoid in the transmission. On some Camaros and Firebirds equipped with manual transmissions, this terminal is connected to the dash panel mounted Shift Light, allowing the ECM to illuminate the light by supplying a ground to this terminal. DELETE if you are not using the ECM to control the TCC function or if you are using a transmission which does not incorporate a TCC.

A-8
Circuit #461
SERIAL DATA

Connected to terminal E and, in some applications, also Terminal M of the ALDL connector (Figure 10 page 14).

This circuit provides what is referred to as Serial Data output. Serial Data is the term used to describe the data stream of information transmitted by the ECM from this terminal to the ALDL terminals A and M in the form of a variable voltage (2-5V) signal representing words and other information which is in turn decoded by a computer chip in the SCAN tool into a form which can be displayed on the SCAN tools read-out screen.

A-9
Circuit #451
DIAGNOSTIC TERMINAL

Connected to Terminal B of the ALDL connector (Figure 10 page 14).

This circuit is referred to as the Diagnostic Test circuit. The ECM will enter one of four diagnostic modes depending on the resistance value placed between ALDL Terminal B and ALDL Terminal A. Terminal A of the ALDL connector should be connected to the ganged common ground circuit comprised of ECM Terminals A-12, D-3, D-6, and D-10 which is, in turn, connected to a secure engine ground. Grounding Terminal B of the ALDL by jumpering it to Terminal A, with the ignition key turned to the ON position, engine NOT running, causes the ECM to enter the Diagnostic Mode. For more information, refer Part Six, Trouble Codes on page 34.

A-10
Circuit #437
VSS SIGNAL

Connected to the VSS buffer.

Input from the VSS buffer provides a miles-per-hour reference to the ECM which it uses to control the TCC function. The ECM applies and monitors +12V on this circuit. The VSS buffer, which alternately grounds this circuit when the drive wheels are turning, effectively pulses this supplied voltage. The ECM then calculates vehicle speed based on the time between pulses. This pulsing action takes place 2,000 times per mile. If the VSS is not used, ECM Terminal B-10 (the park/neutral switch connection) should be grounded to the ECMs ganged common ground wire circuit (refer  System Ground) which is, in turn, connected to a secure engine ground. With B-10 grounded, the VSS systems self-diagnostics will not set a trouble code to indicate a VSS problem. For more information, refer page 16.

DELETE if VSS is not used.
A-11
Circuit #476 or
ANALOG GROUND

Connected to Terminal B of the MAF sensor.

This circuit provides the analog ground for the MAF sensor.

DO NOT connect to common engine/chassis ground.

System Ground

A-12
Circuit #450
SYSTEM GROUND

Connected to Terminal B (Design 1) or F (Design 2) of the fuel pump relay and should also be connected to the ganged common ground wire circuit from ECM Terminals D-1, D-3, D-6, and D-10 which are, in turn, connected to a secure engine ground.

B-1
Circuit #340
+12V BATTERY supply

This terminal should be connected through a 20 amp fuse which, for our rewiring purposes, we shall refer to as the Battery Fuse (Fuse #1), directly to a constant NON-SWITCHED + 12V source (ie battery). The wire from this terminal can be ganged with the similarly coloured wire from ECM Terminal C-16, as is indicated by the same Circuit #340. Also connected to this same +12V source should be fuel pump relay Terminal E (Design 1) or A (Design 2), MAF sensor power relay Terminal E (Design 1), or A (Design 2), MAF sensor burnoff relay Terminals C and E (Design 1), or A and D (Design 2), and one side of the oil pressure activated fuel pump backup switch.

B-2
Circuit #120
FUEL PUMP SIGNAL

Connected to the wire which runs from Terminal A (Design 1) or E (Design 2) of the fuel pump relay and to the fuel pump power terminal, it is also connected to the junction of similarly coloured wires that connect to the MAF sensor power relay Terminal C (Design 1) or D (Design 2), and the other side of the previously mentioned oil pressure activated fuel pump backup switch. The ECM uses this circuit to monitor the status of the electric fuel pump.

There should be +12V on this circuit whenever the engine is running, or being cranked over by the starter motor, and the ECM is receiving distributor reference pulses, OR whenever the oil pressure activated fuel pump backup switch is closed by engine oil pressure. In addition, the ECM provides +12V to Terminal A-1 for 2 seconds after the ignition key is turned ON without waiting for distributor reference pulses, to enable the fuel pump to run and build up the required pressure for the engine to start (sort of a pre-start priming action). This 2-second interval is also monitored and controlled by this circuit. The monitoring of this circuit also allows a trouble code to be set (Code 54 Page 36) and the check engine light to come ON if the fuel pump relay is defective or if fuel pump voltage is otherwise lost when the engine is running.

B-3
Circuit #453
EST REFERENCE

Connected to one of the four wires which run as a group to the 4-pin distributor plug.

This circuit provides a reference ground between the ECM and the distributor ignition module, to assure there is no voltage drop between these two components.

B-5
Circuit #430
DISTRIBUTOR REFERENCE

Connected to one of the four wires which run as a group to the 4-pin distributor plug.

This circuit provides the ECM with rpm and crankshaft position input. Should this circuit become open or grounded, the engine will not run because the ECM will not pulse the injectors.

B-6
Circuit #963
VATS (Pass-Key)

Connected to Terminal P or A-2 (depending on year and model) of the VATS decoder module.

This circuit provides input from the VATS decoder module which the ECM requires before it will pulse the injectors on vehicles that are factory equipped with a VATS system. If there is no wire in this terminal position, the wiring loom being used is from a vehicle that was not equipped with a VATS system and the following information DOES NOT apply! ! If there IS a wire in this terminal position, the wiring loom being used was from a vehicle equipped with a VATS system and MUST have the MEM-CAL replaced with one from a system that did not utilise VATS, or you must add an after-market VATS-defeater unit to the system. This is explained in detail on page 3. Once the replacement MEM-CAL is substituted in the ECM, this circuit can be deleted.

If there IS a wire in this terminal, and a non- VATS MEM-CAL is not substituted, or if a VATS defeater is not added to the system, the engine WILL NOT START!

If you are using any 89 system, which will be equipped with a VATS module you cannot install an 86-88 non-VATS MEM-CAL because the replacement would not be properly calibrated for the 89 systems cold-start specifications. The 89 system does not use a separate cold-start valve as do the 86-88 units. In this case it is necessary to use an after-market VATS defeater unit or a custom MEM-CAL that will provide the correct cold start calibration and also have the VATS system input requirement overridden.

Without some sort of cold start enrichment the engine will be VERY hard to start!
B-7
Circuit #485
ESC SIGNAL

Connected to Terminal C of the ESC module plug .

This circuit provides input from the ESC module to the ECM, which the ECM uses to control spark timing (knock retard) input to the ECM. The ESC module should be powered by a connection from the gauges fuse (Fuse #3-Circuit #39) to ESC module Terminal B. In the OEM hook-up, this +12V supply is normally routed through Circuit #439, the ECM fuse (Fuse #2 for our rewiring purposes). While doing the rewiring, we prefer to provide the power for the ESC through Circuit #39,the gauges Fuse #3, as this effectively isolates the ECM as the only component fused by the ECM fuse (Fuse #2). ESC module Terminal D should be connected to the ganged common ground wires from ECM Terminals A-12, D1, D-3, D-6, and D-10 (refer .) which, in turn, should be connected to a secure engine ground. ESC Terminal E should be routed directly to the engine block mounted Knock-Sensor unit.

B-8
Circuit #59
A/C SIGNAL

Connected to the positive terminal of the AC compressor clutch wiring plug. Connected in this manner, this circuit will provide a +12V input to the ECM to inform it that the AC compressor clutch is engaged and the ECM will then proceed to adjust the idle speed, by controlling the ISC unit, to compensate for AC compressor clutch engagement.

DELETE if not using an air conditioning system.
B-10
Circuit #434
PARK / NEUTRAL SIGNAL

Connected to the park/neutral switch connector Terminal B.

When the transmission selector lever is placed in the park or neutral position, this switch completes the circuit from this terminal to ground. Should you elect not to install a park/neutral switch, this terminal must be connected to the ganged common ground wire circuit terminals that include ECM terminals A-12, D-1, D-3, D-6, and D-10 (refer  System Ground.). Grounded this way, it effectively informs the ECM that the transmission is in neutral and also eliminates trouble codes that would be set if the VSS and EGR circuits are deleted or not properly connected. The VSS and EGR circuits diagnostics are such that they will not set a trouble code if the transmission is in park or neutral. Grounding Terminal B-10 effectively fools the ECM by telling it the transmission is always in neutral. Conversely, should you elect to use and wire the park/neutral switch, as designed, the lack of VSS and EGR inputs WILL light the Check Engine/Service Engine Soon light whenever the ECM does not see the proper inputs, thus requiring both a functional VSS and EGR system.

B-12
Circuit #998
MAF INPUT

Connected to MAF sensor connector Terminal C. The ECM provides +5V on this circuit to the MAF sensor, and monitors the changes in voltage caused by the MAF sensors adjustments to maintain a constant 212F temperature of the Hot-Wire..

C-1
Circuit #335
FAN RELAY CONTROL

Connected to Terminal B of the fan control relay.

This circuit allows the ECM to control the operation of the engine cooling fan relay by grounding this terminal, thus providing ECM control of the electric cooling fan operation. We suggest hooking this circuit up when an electric fan is used, even if another method of controlling the fan relay is used (ie manual switch, engine mounted temperature switch, etc.) to provide a back-up circuit which ensures fan operation in the remote chance that one of the other control circuits may malfunction.

If you are using an electric engine cooling fan in your installation, it should also be wired to run whenever the AC compressor clutch is engaged.

This can be most easily accomplished by adding a second fan control relay to the system. This second relay should be activated by the same circuit (Terminal B8 Circuit #59) which provides the ECM with the AC on signal.

A second relay is required for this application because the stock fan relay is activated by supplying a ground, whereas the AC on signal is a + 12V input, thus requiring the use of a second relay, to allow either circuit to independently control the fan operation Para 92. Page 29 refers).

DELETE if not using an electric fan.
C-2
circuit #429
AIR SWITCH (DIVERT SOLENOID)

refers. Connected to the Divert Air Control Solenoid connector (BLACK) of the AIR valve.

This circuit allows the ECM to activate the Divert Air Control Solenoid portion of the AIR valve assembly by supplying a ground through terminal C2. The +12V supply is supplied via the gauges fuse (Fuse#3-Circuit #39). As indicated earlier, while the ECM controls this circuit, it does not monitor it, so the AIR system and this circuit can be eliminated with no negative effects on ECM operation or diagnostics.

DELETE if removing AIR valve and pump assembly.
C-3
Circuit #444
IAC COIL B LO
C-4
Circuit #443
IAC COIL B Hi
C-5
Circuit #441
IAC COIL A Hl
C-6
Circuit #442
IAC COIL A LO

These four wires run directly, as a group, to the 4-pin IAC unit connector mounted on the injector throttle body assembly allowing the ECM to control engine idle speed by moving the IAC valve to control air flow around the throttle plates. It does this by sending voltage pulses referred to as counts, to the proper motor winding to either activate the in or out operation of the valve.

CAUTION
DO NOT, under ANY circumstances, apply +12V battery voltage across the IAC terminals! Doing so will permanently damage the motor windings!
C-7
Circuit #925
A/T O-D SWITCH SIGNAL
c-8
Circuit #905
M/T O-D REQUEST

This circuit is sometimes used, in Corvette installations, to provide an override of the TCC function if the shift selector is in a position other than overdrive. If there is a wire in this terminal position, and you are using the ECM and a VSS to control the TCC function, grounding the terminal to the common ganged ground circuit A-12, D1, D-3, D-6, D-10 (refer  System Ground), will not allow the TCC function to operate below 40 mph. In systems originally used in Corvettes with manual 4-speed plus electronically controlled overdrive transmissions, this circuit receives input from a control button on the shift lever or console which connects to this same terminal, to activate and deactivate the overdrive function of the manual transmission.

DELETE If you are not using the ECM to control the TCC function or if you are using a transmission which does not incorporate a TCC.
C8
Circuit #446
A/T O-D 4TH GEAR
c8
Circuit #902
M/T O-D REQUEST (4SPD Man w/OD)

Connected to the TH-700-R4 transmission 4-pin connector in some applications, and provides an input to the ECM to signal 4th gear (OD) engagement. In some Corvette manual 4-speed plus overdrive applications, this circuit is connected to a switch which prohibits overdrive engagement when the transmission is in 1st (low) gear.

The circuits controlled by ECM Terminals C-7 and C-8 are sometimes not used at all in some years and models, and on other years and models, the manual transmission functions may be in different combinations than those indicated here (ie in some year/model combinations C-8 is used as an M/T O.D. request instead of C-7, etc).

Since the vast majority of non-OEM usage will be with an automatic transmission, this will not normally create a problem. This information is provided in an attempt to be as comprehensive as possible, and does again point out that its a good idea to have a GM shop manual available for the specific year/model vehicle from which you have obtained the wiring loom assembly.

C-10
Circuit #410
COOLANT TEMPERATURE SIGNAL

Connected to the coolant temperature sensor. This circuit provides coolant temperature input to ECM.

C-12
Circuit #472
MAT SIGNAL

Connected to the MAT sensor. This circuit provides inlet air temperature input to the ECM.

C-13
Circuit #417
TPS SIGNAL

Connected to terminal B of the 3-pin TPS connector. This circuit provides a TPS input voltage to the ECM, allowing the ECM to determine the amount of throttle opening, since the input voltage signal changes relative to throttle opening.

C-14
Circuit #416
TPS +5V REFERENCE

Connected to terminal C of the 3-pin TPS connector. This circuit provides the +5V reference signal to the TPS.

C-15
Circuit #935
EGR DIAGNOSTIC SWITCH

Connected to the EGR diagnostic temperature switch on the EGR valve assembly. This circuit allows the ECM to monitor EGR operation. The EGR diagnostic switch, which threads into the EGR valve base, is normally open when cold, and closes with heat, provided by the exhaust gas when the EGR is operating. The ECM monitors the operation of this switch and will set a trouble code 32 (page 35) and light the Check Engine/Service Engine Soon light if it sees input outside its preprogrammed parameters. If you are removing the EGR system, this circuit can be deleted if the park/neutral switch connector B-10 is connected to the ganged common ground wire circuit connected to ECM terminals A-12, D-1, D-3, D-6, and D-10 (refer  System Ground). Also, see ECM terminal A-4 listing for more information.

DELETE if not using the EGR valve.
C-16
Circuit #340
+12V BATTERY supply

This terminal should be connected through a 20 amp fuse which, for our rewiring purposes, we shall refer to as the Battery Fuse (Fuse #1 ), directly to a constant NON-SWITCHED +12V source (i.e. battery). The wire from this terminal can be ganged with the similarly coloured wire from ECM Terminal B-1 as is indicated.

Also connected to this same +12V source should be fuel pump relay terminal E (Design 1) or A (Design 2), MAF sensor power relay Terminal E (Design 1) or A (Design 2), MAF sensor burn-off relay terminals C and E (Design 1) or D and A (Design 2), and one side of the oil pressure activated fuel pump back up switch.

D-1
Circuit #450
SYSTEM GROUND

Connected to the ganged common ground wire circuit along with ECM Terminals A-12, D-3, D-6, and D-10 (refer  System Ground) which are, in turn, connected to a secure engine ground.

D-2
Circuit #452
TPS, CTS, MAT +5v RETURN

Connected to Terminal Aof the 3-pin TPS connector. This circuit is the common +5V return line for the TPS, MAT and CTS, (which is also connected to the MAT, and coolant temperature sensor (CTS) connectors).

D-3
Circuit #450
SYSTEM GROUND

Connected to the ganged common ground wire circuit together with ECM terminals A-12, D-1, D-6, and D-10 (refer  System Ground), which are, in turn, connected to a secure engine ground.

D-4
Circuit #423
EST CONTROL

Connected to one of the four wires that run as a group to the 4-pin distributor plug. This circuit allows the ECM to trigger the HEI distributor ignition module. This is also the circuit the ECM uses to actually control timing by advancing or retarding the spark, relative to the reference signal it gets from circuit #430, preprogrammed timing data stored in the MEM-CAL, and input from the ESC Circuit #485.

D-5
Circuit #424
BYPASS

Connected to one of the four wires that run as a group to the 4-pin distributor plug. At about 400 rpm, this circuit applies +5V to the HEI ignition module which switches timing control from the HEI ignition modules internal calibration to the ECM. This circuit includes a separate wiring loom connector, referred to as the Set Timing connector. When disconnected, the Set Timing connector provides a method of setting the base ignition timing on the engine, by eliminating ECM control of the spark timing. When the ignition timing has been set and the Set Timing connector is reconnected, you will find the Check Engine/Service Engine Soon light will be illuminated and a trouble code 42 (page 35) set in the ECM memory. This is normal and indicates the ECMs self diagnostic capabilities are functioning properly.

For more information on Trouble Codes and instructions on the proper procedure to remove Code 42 or other Trouble Codes from the ECMs memory, refer the section on Trouble Codes, on page 34.

D-6
Circuit #413
OXYGEN SENSOR GROUND

Connected to the ganged common ground wire circuit together with ECM Terminals A-12, D-1, D-3, and D-10 (refer  System Ground), which are, in turn, connected to a secure engine ground. This circuit provides the ground for the Oxygen Sensor.

D-7
Circuit #412
OXYGEN SENSOR SIGNAL

Connected to the Oxygen Sensor. The ECM uses this circuit to supply a voltage of approximately 0.45 volts between this terminal and its appropriate ground connector D-6. The Oxygen Sensor varies the voltage within a range of about 1.0 volt if the exhaust is rich, down through about 0.10 volt if the exhaust is lean. The Oxygen Sensor acts like an open circuit and produces no voltage when it is below 600F. Accordingly, a cold sensor, or a break in this circuit causes the system to remain in open loop operation.

D-10
Circuit #450
SYSTEM GROUND

Connected to the ganged common ground wire circuit along with ECM terminals A-12, D-1, D-3, and D-6 (refer  System Ground), which are, in turn, connected to a secure engine ground.

D-11
Circuit #732 or
Circuit #992 or
Circuit #731
A/C PRESSURE
N/A
Circuit ***
FAN SWITCH
   
(colour code and circuit # vary with different vehicles.)

Connected to the air conditioning pressure fan request switch.

This circuit is part of the electric cooling fan control system. In the factory hook-up there is a normally closed pressure sensitive switch installed in the high pressure side (the line between the AC compressor and the condenser) of the air conditioning system. When this switch sees pressure exceeding 233 psi, it opens the contacts to inform the ECM of the high pressure condition. The ECM, in turn, grounds Circuit #335 (ECM Terminal C-1) to activate the fan relay which, in turn, powers the engine cooling fan. When high side pressure drops below 185 psi, the switch closes again and the ECM, in turn, removes the ground from Circuit #335 to make the fan inoperative. It is not necessary to incorporate this circuit when rewiring for a non-OEM application. Simply connect the terminal to the common ganged ground circuit A-12, D-1, D-3, D-6, and D-10 (refer  System Ground) as the factory does when the vehicle is not equipped with air conditioning. This allows the ECM to control the fan circuit from engine coolant temperature alone.

If you are using an electric engine cooling fan in your installation, it should also be wired to run whenever the AC compressor clutch is engaged.

This can be most easily accomplished by adding a second fan control relay to the system that is activated by the same circuit (B-8) which provides the ECM with the AC on signal.

A second relay is required for this application because the stock fan relay is activated by supplying a ground, whereas the AC on signal is a +12V input, thus requiring the use of a second relay, to allow either circuit to independently control the fan operation.

D-12
Circuit #900
MAF BURN-OFF RELAY CONTROL

Connected to the MAF Sensor Burn-off Relay terminal B (Design 1) or F (Design 2). The MAF Sensor uses a hot-wire to determine air flow by measuring the current required to maintain this thin wire at a constant temperature as intake air flow passes over it. Due to contaminants which are always present in the atmosphere, a residue may build up on this sensing wire. To remove this residue, a burn-off cycle is incorporated whenever the ignition is turned OFF after the engine has been running for a specified period of time. The ECM then grounds the terminal to activate the burn-off relay, to provide adequate voltage to the Hot-Wire to heat it to approximately 1,000F and, effectively, remove any contamination.

D-15
Circuit #467
INJ 1-3-5-7

Connected to Fuel Injectors 1, 3, 5, and 7.

D-16
Circuit #468
INJ 2-46-8

Connected to Fuel Injectors 2, 4, 6, and 8.

Circuits #467 and #468 allow the ECM to pulse the fuel injector solenoids at the correct time and for the proper duration, by grounding these terminals. By dividing the injectors and attendant wiring into two groups, the possibility of one defective injector or circuit shutting down the entire system, is avoided. Power for these two sets of injectors is provided through two separately fused circuits: Circuit #639, protected by fuse INJ-1 (Fuse #4) for the 1, 3, 5, and 7 injectors, and Circuit #839, protected by fuse INJ-2 (Fuse #5) for the 2, 4, 6, and 8 injectors, both circuits using PINK/BLACK or BLACK wire, and both circuits being fused with 10 amp fuses.


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