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To pull the codes, jumper pins A and B on the ALDL connector (upper right) and turn ignition switch to run position.
| 12 | No tach signal to ECM | This code will flash whenever the diagnostic terminal is grounded with the ignition turned On and the engine not running. If additional trouble codes are stored in the ECM they will appear after this code code has flashed three times. If this code appears while the engine is running, no reference pulses from the distributor are reaching the ECM. |
| 13 | Oxygen sensor circuit | Check for a sticking or maladjusted throttle position sensor. Check the wiring and connectors from the oxygen sensor. Replace the oxygen sensor. |
| 14 | Coolant sensor/high temp | If the engine is experiencing overheating problems the problem must be rectified before continuing. Check all wiring and connectors associated with the coolant temperature sensor. Replace the coolant temperature sensor. |
| 15 | Coolant sensor/low temp | See above, then check the wiring connections at the ECM. |
| 21 | Throttle position sensor/high | Check for a sticking or maladjusted TPS plunger. Check all wiring and connections between the TPS and the ECM. Adjust or replace the TPS. |
| 22 | Throttle position sensor/low | Check the TPS adjustment. Check the ECM connector. Replace the TPS. |
| 23 | Mixture control solenoid | The mixture control solenoid is open or grounded. |
| 24 | Mixture control solenoid | A fault in this circuit should be indicated only when the vehicle is in motion. Disregard Code 24 if it is set when the drive wheels are not turning. Check the connections at the ECM. Check the TPS setting. |
| 32 | BARO circuit low | Barometric pressure sensor circuit is low. |
| 33 | MAP sensor | Check the vacuum hoses from the MAP sensor. Check the electrical connections at the ECM. Replace MAP sensor. |
| 34 | Vacuum sensor or MAP sensor | Code 34 will set when the signal voltage from the MAP sensor is too low. Instead the ECM will substitute a fixed MAP value and use the TPS to control fuel delivery. Replace the MAP Sensor. |
| 35 | ISC valve | Idle Speed Control error. Replace the ISC. |
| 41 | EST circuit | No distributor reference pulses to the ECM at specified engine vacuum. |
| 42 | Electronic Spark Timing | Electronic Spark Timing bypass circuit or EST circuit is grounded or open. A bad HEI module can cause this code. |
| 43 | Electronic spark control unit | The ESC retard signal has been on for too long or the system has failed a functional check. |
| 44 | Lean exhaust | Check the ECM wiring connections, particularly terminals 15 and 8. Check for vacuum leakage at the carburetor base gasket, vacuum hoses or the intake manifold gasket. Replace the oxygen sensor. |
| 45 | Rich exhaust | Check the evaporative charcoal canister and its components for the presence of fuel. Replace the oxygen sensor. |
| 51 | PROM or MEM-CAL | Make sure that the PROM and/or MEM-CAL is properly installed in the ECM. Replace the PROM and/or MEM-CAL. |
| 52 | CALPAK | Check the CALPAK to insure proper installation. Replace the CALPAK. |
| 53 | EGR valve | Exhaust Gas Recirculation valve vacuum sensor has received improper EGR vacuum. |
| 54 | M/C solenoid | The mixture control solenoid voltage is high at the ECM because of a shorted M/C solenoid circuit and/or faulty ECM. |
| 55 | ECM | Be sure that the ECM ground connections are tight. If they are, replace the ECM. |