Reading Trouble Codes
The ECM stores component failure information under a related trouble code which can be recalled for diagnosis and repair. Read trouble codes by counting SERVICE ENGINE SOON light flashes or with diagnostic Scan tester connected to the ALDL connector. The tester is faster, and capable of reading information which would require testing individual ECM and sensor/solenoid connector terminals with a digital voltmeter. See SCAN TESTER DATA TABLE and SCAN TESTER USAGE.
If Scan tester is not available, SERVICE ENGINE SOON light flashes can be read by grounding ALDL diagnostic terminal with ignition on and engine off. For example, FLASH, FLASH, pause, FLASH, longer pause, indicates Code 21. The first series of flashes are the first digit of trouble code. The second series of flashes are the second digit of trouble code. Trouble codes are displayed starting with the lowest code. Each code is displayed 3 times and will continue as long as ALDL is grounded.
| Code | Probable Cause | ||
|---|---|---|---|
| 12 | No Engine Speed Sensor Reference Pulse To PCM/TCM | ||
| 13 | Open Oxygen Sensor Circuit | ||
| 14 | CTS Voltage Low (Sensor Or Signal Line Grounded) | ||
| 15 | CTS Voltage High (Sensor, Connections, Or Wires Open) | ||
| 21 | TPS Voltage High (Open Circuit Or Misadjusted TPS) | ||
| 22 | TPS Voltage Low (Circuit Grounded) | ||
| 23 | Intake Air Temperature Sensor Voltage High | ||
| 24 | Vehicle Speed Sensor Circuit Open Or Grounded | ||
| 25 | Intake Air Temperature Sensor Voltage Low | ||
| 28 (1) | Pressure Switch Manifold Range Circuit Open Or Shorted | ||
| 31 | Turbocharger Wastegate Overboost | ||
| 32 | EGR Error (Improper Vacuum Signal) | ||
| 33 | MAP Voltage High (Circuit Open Or Short To Voltage) | ||
| 34 | MAP Voltage Low (Circuit Open Or Short To Ground) | ||
| 35 | IAC System Fault | ||
| 39 (1) | TCC Stuck Off (Faulty TCC Solenoid) | ||
| 42 | EST Circuit Fault | ||
| 43 | ESC Fault | ||
| 44 | Lean Exhaust Indicated | ||
| 45 | Rich Exhaust Indicated | ||
| 51 | Improperly Installed/Faulty PROM/MEM-CAL | ||
| 52 | Fuel CAL-PAC Missing | ||
| 53 | System Voltage High (Charging System Problem) | ||
| 54 | Fuel Pump Circuit Voltage Low | ||
| 55 | Faulty ECM | ||
| 58 (1) | TTS High Temperature (Sensor Or Signal Line Grounded) | ||
| 59 (1) | TTS Low Temperature (Sensor, Connections, Or Wires Open) | ||
| 68 (1) | Overdrive Ratio Error (Engine RPM Greater Than Input Speed) | ||
| 73 (1) | Force Motor Commanded Amperage Differs From Return | ||
| 75 (1) | System Voltage Low (Charging System Problem) | ||
| 81 (1) | QDM Solenoid "B" Monitored Voltage Differs From Commanded | ||
| 82 (1) | QDM Solenoid "A" Monitored Voltage Differs From Commanded | ||
| 83 (1) | QDM TCC Monitored Voltage Differs From Commanded | ||
| 85 (1) | Undefined Gear Ratio (Input Or Output Sensor Failure) | ||
| 86 (1) | Shift Solenoid "B" Stuck On (Commanded Gear Not Engaged) | ||
| 87 (1) | Shift Solenoid "B" Stuck Off (Commanded Gear Not Engaged) | ||
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