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Trouble Code Listing

The following is a list of trouble codes that can be set by the ECM to indicate problems with either the sensor or the wiring of specific circuits. Some suggestions have been made to the possible cause and remedy of the Trouble Code. These are only a general guide, and are not intended as a trouble shooting tool.

Trouble Code 12, ECM ON

Code 12 indicates the ECM is ON and is not receiving any reference pulses from the distributor. This is a normal code with the ignition ON and the engine not running, and is used for verification of ECM operation during the Diagnostic Circuit Check. Code 12 is not stored in the ECMs memory and will only flash when ALDL terminal B is jumpered to ground (ALDL terminal A) with the ignition ON and the engine not running. Additional trouble codes stored in the ECM will appear after this code has flashed three times.

Trouble Code 13, OXYGEN SENSOR - OPEN CIRCUIT

Code 13 indicates an open in the oxygen sensor circuit (circuit #412) or a possible defective oxygen sensor unit. A sticky or misadjusted Throttle Position Sensor will also cause this Trouble Code. See Throttle Position Sensor.

Trouble Code 14 COOLANT TEMPERATURE - HIGH TEMP. INDICATION.

Code 14 indicates an overheating problem which must be rectified before continuing. A defective coolant temperature sensor (See Coolant Temperature Sensor) or a short to ground in circuit # 410 may also be a cause. Check wiring and connections first.

Trouble Code 15 COOLANT TEMPERATURE - LOW TEMP. INDICATION

Code 15 indicates inefective thermostat operation. A defective coolant temperature sensor or an open in circuit #410 can also be a problem. If a Code 21 or 23 is set along with Code 15, circuit #452 should also be checked for an open condition.

Trouble Code 21 TPS SENSOR - VOLTAGE HIGH

Code 21 indicates a problem with the TPS sensor, or an open in circuit #452. Check for a sticking or misadjusted TPS. See Throttle Position Sensor.

Trouble Code 22 TPS SENSOR - VOLTAGE LOW

Code 22 indicates a defective or maladjusted TPS sensor, a short to ground or open in circuits #416 and #417. Check TC 21 for correct operation.

Trouble Code 23 MAT SENSOR-LOW TEMP. INDICATION

Code 23 indicates a defective MAT sensor, or an open in circuits #452 or #472.

Trouble Code 24 VSS FAULT

Code 24 indicates a defect in the VSS or an open or short to ground in circuit #437. Should only indicate when the vehicle is in motion. Disregard if vehicle is stationary. If ECM terminal B-10 is connected to the ganged common ground circuit A-12, D-1, D-3, D-6, and D-10 (See System Ground), Code 24 will not set even though there is a nonfunctional or defective VSS circuit; conversely, if terminal B-10 is NOT connected to ground and there is no functional VSS system, the ECM will set a Code 24 when the vehicle is driven!

Trouble Code 25 MAT SENSOR - HIGH TEMP. INDICATION

Code 25 indicates a defective MAT sensor, or a short to ground in circuit #472. The voltage from the MAT to the ECM should be about 4 Volts DC.

Trouble Code 32 EGR SYSTEM FAULT

Code 32 indicates a malfunctioning EGR valve, a malfunctioning EGR temperature diagnostic switch, or an open or short to ground in circuit #935 or #999 (depending on year and model). The diagnostic switch should close at about 2 inches of vacuum. If the EGR system is not used, ECM terminal B-10 should be connected to the ganged common ground circuit A-12, D-1, D-3, D-6, and D10 (See System Ground). If terminal B-10 is connected in this manner, Code 32 will not set, even if the EGR is missing or nonfunctional; conversely if terminal B-10 is NOT connected to ground and the EGR system is removed, the ECM will set a Code 32 when the vehicle is driven.

Trouble Code 33 MAF - HIGH AIR FLOW

Code 33 indicates a defective MAF sensor (See Mass Air Flow Sensor), or a problem in the MAF circuitry. Check terminal C on the MAF Sensor. It should be about .5V at idle and 4.7 V at Wide Open Throttle.

Trouble Code 34 MAF- LOW AIR FLOW

Code 34 indicates a defective MAF sensor, or a problem in the MAF circuitry.

Trouble Code 36 MAF BURN-OFF FAULT

Code 36 indicates a problem in the MAF burn-off circuitry.

Trouble Code 41 CYLINDER SELECT ERROR

Code 41 indicates a faulty or incorrect MEM-CAL, or an open in circuit #450 at ECM terminal D-3. ECM #1227165 is used in different engine/vehicle applications other than the 86-89 TPI V-8 usage. When used in these other systems, MEM-CAL units with different calibrations are used, and ECM terminal D-3 is not connected to ground. If the correct ECM has been verified, then check for 12V at ECM Terminal D-3 with ECM C-D connector removed. If positive, the connector may be faulty.

Trouble Code 42 EST FAULT

Code 42 indicates a faulty ignition module, or an open or short to ground in circuit #424, or a short in circuit #423. Check connections between HEI module and EST and the by-pass terminals B4 and D5. HEI Module may be faulty (See Distributor). A Code 42 should always be present, after the set timing connector has been disconnected, to set engine base timing. As previously mentioned, removing the Battery Fuse (  Battery Fuse 20A) for 30 seconds will clear the code from the ECMs memory.

Trouble Code 43 ESC FAULT

Code 43 indicates a faulty ESC module, a faulty knock sensor, or a problem in the related wiring circuits. There should be over 6 Volts at ECM A-B connecor terminal 7 (unless system is detecting detonation).

Trouble Code 44 OXYGEN SENSOR LEAN MIXTURE INDICATION

Code 44 indicates a defective oxygen sensor unit, circuit #412 shorted to ground, or the existence of some other condition (ie low fuel pressure, fuel contamination, etc.) which would cause a lean mixture condition. ECM Terminals D6 (See D-6) and D7 (See D-7) should be checked and then inspect hoses and intake manifold gaskets.

Trouble Code 45 OXYGEN SENSOR RICH MIXTURE INDICATION

Code 45 indicates a defective oxygen sensor unit, or some other condition (ie high fuel pressure, leaking injector, fouled spark plug, etc.), which would cause a rich mixture condition. Also check the charcoal canister for fuel.

Trouble Code 46 VATS FAULT

Code 46 indicates a problem with the VATS module or circuitry. If the engine will not start and a Code 46 is present, the MEM-CAL must be changed to one from a vehicle which was not originally equipped with a VATS (86-88 Camaro-Firebird). For more information on VATS, see ECM terminal listing B-6 on Table 3 and also  B-6.

Trouble Code 51 PROM ERROR

Code 51 indicates an incorrect, or improperly installed PROM.

Trouble Code 52 CAL-PAK ERROR

Code 52 indicates a faulty or incorrect CAL-PAK.

Trouble Code 53 SYSTEM OVER VOLTAGE

Code 53 indicates system voltage at ECM terminal B2 in excess of 17.1 V for more than 2 seconds. A faulty charging system may be the cause.

Trouble Code 54 FUEL PUMP CIRCUIT- LOW VOLTAGE

Code 54 indicates a defective fuel pump relay, low voltage (below 2V) on circuit #120, or the loss of voltage (for more than 1.5 seconds) to the fuel pump while the engine is running. If the Fuel pump relay circuit and connections are good, check the oil pressure switch.

Trouble Code 55 ECM FAULT

Trouble Code 55 indicates ECM failure, usually due to insufficient grounding and/or loose terminals and connectors.

In addition to the above indicated individual possible problem areas, all trouble codes except #51, 52, and 53 could also have a defective ECM listed as one of the possible reasons for the trouble code being displayed. This is another place to indicate to you that you should consider having on hand the proper year and model GM service manual. The trouble code information above is provided as a basic reference. The individual service manuals provide extensive, detailed diagnostic procedures for further troubleshooting the problem areas indicated by the above codes.

Table 5 - Trouble Code Flash Sequences 
Trouble Code
Flash Sequence (after TC 12)
Circuit or System
Code 12
1 Flash, Pause, 2 Flashes
No reference pulses to ECM
Code 13
1 Flash, Pause, 3 Flashes
Oxygen Sensor Circuit
Code 14
1 Flash, Pause, 4 Flashes
Coolant Sensor Circuit
Code 15
1 Flash, Pause, 5 Flashes
Coolant Sensor Circuit
Code 21
2 Flashes, Pause, 1 Flash
Throttle Position Sensor
Code 22
2 Flashes, Pause, 2 Flashes
Thrpttle Position Sensor
Code 23
2 Flashes, Pause, 3 Flashes
Manifold Air Temperature Sensor
Code 24
2 Flashes, Pause, 4 Flashes
Vehicle Speed Sensor
Code 25
2 Flashes, Pause, 5 Flashes
Manifold Air Temperature Sensor
Code 32
3 Flashes, Pause, 2 Flashes
EGR System
Code 33
3 Flashes, Pause, 3 Flashes
Mass Air Flow Sensor
Code 34
3 Flashes, Pause, 4 Flashes
Mass Air Flow Sensor
Code 35
3 Flashes, Pause, 5 Flashes
Idle Air Control
Code 41
4 Flashes, Pause, 1 Flash
Cylinder Select Error
Code 42
4 Flashes, Pause, 2 Flashes
Electronic Spark Timing
Code 43
4 Flashes, Pause, 3 Flashes
Electronic Spark Control
Code 44
4 Flashes, Pause, 4 Flashes
Lean Exhaust
Code 45
4 Flashes, Pause, 5 Flashes
Rich Exhaust
Code 51
5 Flashes, Pause, 1 Flash
ECM PROM
Code 52
5 Flashes, Pause, 2 Flashes
Fuel CALPACK
Code 53
5 Flashes, Pause, 3 Flashes
System Over-Voltage
Code 54
5 Flashes, Pause, 4 Flashes
Fuel Pump Circuit
Code 55
5 Flashes, Pause, 5 Flashes
ECM Fault
     


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