Test 9: Tachometer Inaccurate

Perform INSTRUMENT PANEL CLUSTER (IPC) DIAGNOSTIC SYSTEM CHECK before proceeding. See INSTRUMENT PANEL CLUSTER (IPC) DIAGNOSTIC SYSTEM CHECK under SYSTEM TEST. If INSTRUMENT PANEL CLUSTER (IPC) DIAGNOSTIC SYSTEM CHECK has been performed, go to next step.
Turn ignition switch to OFF position. Connect scan tool to Data Link connector (DLC). Turn ignition switch to ON position. Using scan tool, select POWERTRAIN, ENGINE DATA, then DATA. Start engine. Compare engine speed displayed on scan tool with tachometer reading. If scan tool does not agree with tachometer, turn engine off, then go to next step. If scan tool agrees with speedometer, turn engine off, then check for an intermittent problem caused by poor connections, a break in wire insulation, or a broken wire inside insulation. See WIRING DIAGRAMS .
Using a Digital Multimeter (DMM) in AC voltage scale, select Frequency. Remove IPC. See INSTRUMENT PANEL CLUSTER (IPC) under REMOVAL & INSTALLATION. Using DMM connected to ground, backprobe IPC connector terminal A2, tachometer signal circuit (White wire). Start engine. Monitor DMM while running vehicle up to 800 RPM (as displayed on scan tool). If frequency is 18-25 Hz, go to next step. If frequency is not 18-25 Hz, go to step 5.
Replace IPC. See INSTRUMENT PANEL CLUSTER (IPC) under REMOVAL & INSTALLATION. After repair, go to step 7.
Check for open, short to ground or short to voltage in tachometer signal circuit (White wire). See WIRING DIAGRAMS . Repair circuit as necessary. After repair, go to step 7. If no problem is found, go to next step.
Reprogram VCM using special manufacturer's equipment. After repair, go to next step.
Check tachometer operation. If system operates properly, repair is complete. If problem still exists, return to step 3.