Diagnostic Trouble Codes - 1985
Chevrolet
| 12 | No Reference Pulse |
| 13 | Oxygen Sensor Circuit |
| 14 | Coolant Sensor Shorted |
| 15 | Coolant Sensor Circuit Open |
| 21 | Throttle Position Sensor (TPS) Signal Voltage High |
| 23 | Mixture Control (M/C) Solenoid Voltage Low |
| 24 | Vehicle Speed Sensor (VSS) Circuit |
| 32 | BARO Sensor Voltage Low |
| 34 | Differential Pressure (VAC) Sensor - Voltage Incorrect |
| 41 | No Distributor Reference Signal |
| 42 | Electronic Spark Timing (EST) or Bypass Fault |
| 44 | Lean Exhaust Indication |
| 45 | Oxygen Sensor Circuit (Rich Exhaust Indicated) |
| 51 | PROM Error |
| 53 | Exhaust Gas Recirculation (EGR) Control Error |
| 54 | Mixture Control Solenoid (M/C) Voltage High |
To extract a trouble from the computer for diagnostic purposes, the Assembly Line Communication Link (ALDL) connector is used.
Ground terminals A and B with the ignition "ON" and engine not running. The system will enter the diagnostic mode. In this mode, the computer will display a 12, three consecutive times, by flashing the "CHECK ENGINE", "SERVICE ENGINE SOON" or "MALFUNCTION INDICATOR LAMP" or light. A 12 consists of one flash, a short pause, then two flashes in rapid succession.
After 12 is displayed, any stored trouble s will be displayed by flashing the "CHECK ENGINE", "SERVICE ENGINE SOON" or "MALFUNCTION INDICATOR LAMP" light. All s are displayed 3 times each then a 12 will repeat. In the diagnostic mode, the computer will also energize all computer controlled relays and solenoids.
ALDL Connector (Located Underdash)
The ALDL diagnostic connector is located in the passenger compartment.
