Code 12- No Distributor Reference Signal to ECM. This code is not stored in the memory and will only flash while the fault is present. Normal code with the ignition switch in the ON position and the engine not operating. This code is used to tell you that the system is working properly.

Code 13- Oxygen Sensor Circuit. The engine must be operated up to four minutes at part throttle, under road conditions, before this code will set.

Code 14- Shorted Coolant Sensor Circuit. The engine must run for five minutes before this code will set.

Code 15- Open Coolant Sensor Circuit. The engine must run five minutes before this code will set.

Code 21- Throttle Position Sensor (TPS) ciruit voltage high (open circuit or misadjusted TPS). The engine must run 10 seconds, at specified curb idle speed before this code will set.

Code 22- Throttle Position Sensor (TPS) circuit voltage low (grounded circuit or misadjusted TPS). The engine must run 20 seconds at specified curb idle speed.

Code 23- (1985-87) Mixture Control Solenoid circuit opened or grounded. (1988-90) Manifold Air Temperature low temperature indication.

Code 24- Vehicle Speed Sensor (VSS) circuit. The vehicle must operate up to 2 minutes, at road speed before this code will set.

Code 25- (1988-90) Manifold Air Temperature high temperature indication.

Code 32- (1985-87) Barometric Pressure Sensor (BARO) circuit low. (1988-90) Exhaust Gas Recirculation vacuum switch shorted, switch not closed after the ECM has commanded for a specific time period or EGR solenoid in open.

Code 33- (1988-90) Manifold Absolute Pressure low vacuum.

Code 34- Vacuum Sensor or Manifold Absolute Pressure (MAP) circuit. The engine must be operated up to 2 minutes at the specified curb idle before this code will set.

Code 35- Idle Speed Control (ISC) switch circuit shorted. Up to 70% TPS for over 5 seconds.

Code 41- (1985-87) No Distributor Reference Signal to ECM at specified engine vacuum. This code will store in the memory.

Code 42- Electronic Spark Timing (EST) bypass circuit or EST circuit grounded or open.

Code 43- Electronic Spark Control (ESC) retard signal for too long of a time. Will cause retard in EST signal.

Code 44- Lean Exhaust Indication. The engine must operate for 2 minutes, in the closed loop mode and at part throttle before this code will set.

Code 45- Rich Exhaust Indication. The engine must operate for 2 minutes, in the closed loop mode and at part throttle before this code will set.

Code 51- Faulty or improperly installed calibration unit (PROM), MEM-CAL, or ECM. It takes up to 30 seconds before this code will set.

Code 53- (1985-87) Exhaust Gas Recirculation (EGR) valve vacuum sensor has noted improper EGR control vacuum. (1988-90) System overcharged indicates a basic alternator problem.

Code 54- (1985 Carbureted) Mixture Control Solenoid voltage high at the ECM as a result of a shorted M/C solenoid circuit and/or a faulty ECM. (1986-90) Fuel pump low voltage.

Code 55- (later models) Faulty ECM.