Diagnostic Procedures
- Perform On-Board Diagnostic (OBD) System Check. After performing OBD system check, go to next step.
- Turn ignition on, with engine off. Using scan tool, command upshift light on and off. If shift light turns on and off with each command, see DIAGNOSTIC AIDS. If light does not turn on and off with each command, go to next step.
- Turn ignition off. Disconnect PCM connector containing the light control circuit. Turn ignition on. If shift light illuminates, go to step 5). If shift light does not illuminate, go to next step.
- Using a fused jumper wire, jumper shift light control circuit in PCM harness connector and ground. If shift light illuminates, go to step 6). If shift light does not illuminate, go to step 7).
- Repair short to ground in upshift light control circuit. After repairs, go to step 9).
- Check PCM connections. Repair as necessary. After repairs, go to step 9). If connections are okay, go to step 8).
- Check for faulty light bulb, open ignition feed to bulb, open control circuit or circuit shorted to battery voltage. Repair as necessary. After repairs, go to step 9).
- Replace PCM. Program replacement PCM using required equipment. After repair is completed, go to next step.
- Using scan tool, select DTC, CLEAR INFO function. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1664. Operate vehicle within conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool did not indicate that this test ran and passed, repeat step 2).
- Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.