Chart A-2 - No ALDL Data, No Code 12 Or Trans/Service Engine Soon Light On

Fig 1: Chart A-2 Component Diagram

Courtesy of GENERAL MOTORS CORP.

NOTE: Test numbers refer to numbers on diagnostic chart.

1. If Code 12 does not flash, ensure "Scan" tool is working by testing another vehicle. If "Scan" tool and circuit 1061 are okay, PCM/TCM or PROM/MEM-CAL may be cause of no ALDL data.
2. If TRANS or SERVICE ENGINE SOON light goes off (with PCM/TCM disconnected), circuit 419/1234 is not shorted to ground.
3. This step checks for open diagnostic circuit 451.
4. TRANS or SERVICE ENGINE SOON light control circuit is okay. Replace PCM/TCM and/or PROM/MEM-CAL.

Fig 2: Chart A-2 Troubleshooting Diagnostic Flow Chart

Courtesy of GENERAL MOTORS CORP.