Instrument Cluster Tachometer Malfunctioning
- If BFC diagnostic system check was performed, go to next step. If BFC diagnostic system check was not performed, see procedures in BODY CONTROL MODULE
article.
- Connect scan tool. Start engine. Using scan tool, read BFC-to-instrument cluster data. If tach signal display is ACTIVE, go to step 5). If tach signal display is not ACTIVE, go to next step.
- Using DVOM set on AC voltage, check voltage at tach test point located in underhood wiring harness junction block. See Fig 1
. If AC voltage exists, go to next step. If AC voltage does not exist, locate and repair problem in PCM system. See appropriate TESTS W/CODES
article in ENGINE PERFORMANCE section:
- Disconnect instrument cluster Gray, 24-pin connector. Using DVOM set on AC voltage, check voltage of circuit No. 121 (White wire) at instrument cluster connector terminal A7. See Fig 2
. If AC voltage exists, go to next step. If AC voltage does not exist, go to step 6).
- Replace instrument cluster. See INSTRUMENT CLUSTER
under REMOVAL & INSTALLATION. Recheck system operation.
- Disconnect underhood wiring harness junction block Brown, 30-pin connector C3. Using DVOM set on DC voltage, check voltage between underhood wiring harness junction block harness connector C3 terminal F8 (White wire) and ground. If zero volts exist, go to step 8). If zero volts does not exist, go to next step.
- Repair short to voltage in circuit No. 121 (White wire) between underhood wiring harness junction block connector C3 and instrument cluster. Recheck system operation.
- Using DVOM, check resistance between underhood wiring harness junction block harness connector C3 terminal F8 (White wire) and ground. If resistance is infinite, go to step 10). If resistance is not infinite, go to next step.
- Repair short to ground in circuit No. 121 (White wire) between underhood wiring harness junction block connector C3 and instrument cluster. Recheck system operation.
- Using DVOM, check resistance between underhood wiring harness junction block harness connector C3 terminal F8 (White wire) and instrument cluster harness connector terminal A7 (White wire). If resistance is 0-2 ohms, go to step 12). If resistance is not 0-2 ohms, go to next step.
- Repair open in circuit No. 121 (White wire) between underhood wiring harness junction block connector C3 and instrument cluster. Recheck system operation.
- Replace underhood wiring harness junction block. Recheck system operation.
Courtesy of GENERAL MOTORS CORP.
Courtesy of GENERAL MOTORS CORP.