Trouble Code Identification
WARNING: This page does not describe the selected car, but rather 22 other vehicles, including the 1991 GMC Vandura Special, 1991 GMC Vandura, 1991 GMC Value Van, 1991 GMC Suburban, and 1991 GMC Rally Camper Special. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
Trouble codes retrieved from PCM/TCM may be either engine or transmission related. Engine-related codes are covered in this article. For transmission-related codes, see TESTS W/CODES - TRANSMISSION
article in this section. See TROUBLE CODE IDENTIFICATION table to determine if code is engine or transmission related.
- The DEC system codes indicate failure of a specific sensor and/or circuit. Sensor/circuit diagnosis may indicate replacement of ECM. Code 51 indicates PROM is either improperly installed or has failed.
- Code 52 indicates ECM has failed and must be replaced. If condition is still not corrected after replacing ECM, the following may be the cause.
- An incorrect ECM or PROM application may cause a malfunction, which may or may not set a code.
- The ECM connector may be the problem. Connector terminals may have to be removed from connector to be checked properly.
- PROM failure - Although the PROM rarely fails, it could be the cause of the problem.
- Replacement ECM may be faulty.
- Intermittent problem. Make a careful physical inspection of affected sensor/circuit.
- A shorted solenoid, coil relay, or harness may be the cause of ECM failure. Use Short Circuit Tester (J-34636) to check for short circuits.
TROUBLE CODE IDENTIFICATION
| Code | Probable Cause | ||
|---|---|---|---|
| 12 (1) | No Engine Speed Sensor Reference Pulse To PCM/TCM | ||
| 14 (1) | CTS Voltage Low (Sensor Or Signal Line Grounded) | ||
| 15 (1) | CTS Voltage High (Sensor, Connections, Or Wires Open) | ||
| 21 (1) | TPS Voltage High (Open Circuit Or Misadjusted TPS) | ||
| 22 (1) | TPS Voltage Low (Circuit Grounded) | ||
| 23 (1) | TPS Not Calibrated (.25-1.3 Volts At Curb Idle) | ||
| 24 (1) | Vehicle Speed Sensor Circuit Open Or Grounded | ||
| 28 | Pressure Switch Manifold Range Circuit Open Or Shorted | ||
| 31 (1) | MAP Voltage Low (Circuit Open Or Short To Ground) | ||
| 32 (1) | EGR Error (Improper Vacuum Signal) | ||
| 33 (1) | MAP Voltage High (Circuit Open Or Short To Ground) | ||
| 39 | TCC Stuck Off (Faulty TCC Solenoid) | ||
| 51 (1) | Improperly Installed/Faulty PROM | ||
| 52 (1) | ECM Fault | ||
| 53 (1) | Voltage Reference Overload. | ||
| 58 | TTS High Temperature (Sensor Or Signal Line Grounded) | ||
| 59 | TTS Low Temperature (Sensor, Connections, Or Wires Open) | ||
| 68 | Overdrive Ratio Error (Engine RPM Greater Than Input Speed) | ||
| 73 | Force Motor Commanded Amperage Differs From Return | ||
| 75 | System Voltage Low (Charging System Problem) | ||
| 81 | QDM Solenoid "B" Monitored Voltage Differs From Commanded | ||
| 82 | QDM Solenoid "A" Monitored Voltage Differs From Commanded | ||
| 83 | QDM TCC Monitored Voltage Differs From Commanded | ||
| 85 | Undefined Gear Ratio (Input Or Output Sensor Failure) | ||
| 86 | Shift Solenoid "B" Stuck On (Commanded Gear Not Engaged) | ||
| 87 | Shift Solenoid "B" Stuck Off (Commanded Gear Not Engaged) | ||
|
|||