Retrieving Codes
- Perform diagnostic circuit check before diagnosing vehicle using self-diagnostic system. See appropriate DIAGNOSTIC CIRCUIT CHECK chart under DIAGNOSTIC CODE CHARTS.
- Fault code(s) can be retrieved through either of the 2 diagnostic switch terminals. See Fig 1. One is located in the diagnostic connector in engine compartment, and the other one is located in the fuse block in the passenger compartment.
- To retrieve code(s) using the diagnostic terminal in fuse block, insert spare fuse into diagnostic switch terminal. The ECM will toggle the CHECK ENGINE light, flashing code(s).
- To retrieve code(s) using the diagnostic connector in the engine compartment, ground terminal "B" (diagnostic switch terminal) of connector. The ECM will then output self-diagnostic code(s). Both diagnostic switch terminals, when grounded, will set ignition timing to base timing (XFi w/ESC).
- If no fault codes exist, ECM will flash Code 12. If fault codes are stored, the lowest code will be flashed first. Each code will be displayed 3 times. Proceed to appropriate chart(s) under DIAGNOSTIC CODE CHARTS to diagnose fault codes.
Courtesy of GENERAL MOTORS CORP. FAULT CODE IDENTIFICATION
| Code |
Circuit Affected |
Probable Cause |
| 12 |
System Is Normal |
... |
| Oxygen Sensor |
Open Circuit |
13 |
| Coolant Temp. Sensor |
High Temp. Indicated |
14 |
| Coolant Temp. Sensor |
Low Temp. Indicated |
15 |
| Throttle Switch |
Idle Switch & Throttle Switch Are On |
21 |
| Throttle Position Sensor |
Signal Voltage High |
21 |
| Throttle Position Sensor |
Signal Voltage Low |
22 |
| Manifold Air Temp. Sensor |
Low Temp. Indicated |
23 |
| Vehicle Speed Sensor |
No Speedometer |
24 |
| Manifold Air Temperature |
High Temp. Indicated |
25 |
| MAP Sensor |
Signal Voltage Low, High Vacuum |
31 |
| MAP Sensor |
Signal Voltage High, Low Vacuum |
32 |
| Ignition Signal |
No Signal |
41 |
| Crank Angle Sensor |
No Signal For 2 Seconds |
42 |
| EGR System |
EGR VSV Inoperative |
51 |