Submitted by: Joseph J Sigmon (Joseph.J.Sigmon@lerc.nasa.gov)
| Trouble codes | Circuit or system | Probable cause |
| Code 12 (1 flash, pause, 2 flashes) | No distributor reference pulses 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 has flashed three times. If this code appears while the engine is running, no reference pulses from the distributor are reaching the ECM. |
| Code 13 (1 flash, pause, 3 flashes) | Oxygen sensor circuit | Check for a sticking or misadjusted throttle position sensor. Check the wiring and connectors from the oxygen sensor. Replace the oxygen sensor. |
| Code 14 (1 flash, pause, 4 flashes) | 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. |
| Code 15 (1 flash, pause, 5 flashes) | Coolant sensor/low temp | See above, then check the wiring connections at the ECM. |
| Code 21 (2 flashes, pause, 1 flash) | Throttle position sensor/voltage high | Check for a sticking or misadjusted TPS plunger. Check all wiring and connections between the TPS and the ECM. Adjust or replace the TPS |
| Code 22 (2 flashes, pause, 2 flashes) | Throttle position sensor/voltage low | Check the TPS adjustment. Check the ECM connector. Replace the TPS |
| Code 23 (carbureted) (2 flashes, pause, 3 flashes) | Mixture control solenoid | The mixture control solenoid is open or grounded. |
| Code 24 (2 flashes, pause, 4 flashes) | Vehicle speed sensor | 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. |
| Code 32 (carbureted) (3 flashes, pause, 2 flashes) | BARO circuit low | Barometric pressure sensor circuit low. |
| Code 32 (fuel injected) (3 flashes, pause, 2 flashes) | EGR | Vacuum switch shorted to ground on start-up, switch not closed after the ECM has commanded the EGR for a specified period of time or the EGR solenoid circuit is open for specified period of time. Replace the EGR valve. |
| Code 33 (3 flashes, pause, 3 flashes) | MAP sensor | Check the vacuum hoses from the MAP sensor. Check the electrical connections at the ECM. Replace the MAP sensor |
| Code 34 (3 flashes, pause, 4 flashes) | Vacuum sensor or MAP sensor | Code 34 will set when the signal voltage from the MAP sensor is toa low. Instead the ECM will substitute a fixed MAP value and use the TPS to control fuel delivery. Replace the MAP sensor. |
| Code 35 (carbureted) (3 flashes. pause, 5 flashes) | ISC valve | Idle Speed Control error. Replace the ISC. |
| Code 41 (4 flashes, pause, 1 flash) | EST circuit | No distributor reference pulses to the ECM at specified engine vacuum |
| Code 42 (4 flashes, pause, 2 flashes) | Electronic Spark Timing | Electronic Spark Timing bypass circuit or EST circuit is grounded or open. A malfunctioning HEI module can cause this code. |
| Code 43 (4 flashes, pause, 3 flashes) | Electronic spark control unit | The ESC retard signal has been on for too long or the system has failed a functional check |
| Code 44 (4 flashes, pause, 4 flashes) | Lean exhaust | Check the ECM wiring connections, particularly terminals 15 and B. Check for vacuum leakage at the TBI base gasket, vacuum hoses or the intake manifold gasket. Replace the oxygen sensor |
| Code 45 (4 flashes, pause, 5 flashes) | Rich exhaust | Check the evaporative charcoal canister and its components for the presence of fuel. Replace the oxygen sensor. |
| Code 51 (5 flashes, pause, 1 flash) | PROM or MEM-CAL | Make sure that the PROM or MEM-CAL is properly installed in the ECM. Replace the PROM or MEM-CAL |
| Code 52 (5 flashes, pause, 2 flashes) | CALPAK | Check the CALPAK to insure proper installation. Replace the CALPAK |
| Code 53 (carbureted) (5 flashes, pause, 3 flashes) | EGR valve | Exhaust Gas Recirculation valve vacuum sensor has received improper EGR vacuum. |
| Code 54 (carbureted) (5 flashes, pause, 4 flashes) | 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. |
| Code 54 (fuel injected) (5 flashes, pause, 4 flashes) | Fuel pump | Low fuel pump voltage. Sets when the fuel pump voltage is less than 2 volts when reference pules are being received. |
| Code 55 (5 flashes, pause, 5 flashes) | ECM | Be sure that the ECM ground connections are tight. If they are replace the ECM. |