Test H: Tachometer Inaccurate
NOTE:
Instrument cluster receives engine RPM signal from Powertrain Control Module (PCM).
- Disconnect instrument cluster harness connectors C250 and C251. Turn ignition switch to RUN position. Measure voltage at terminal No. 10 (Red/Yellow wire) at instrument cluster harness connector C250. See Figure . If battery voltage exists, go to next step. If battery voltage does not exist, repair power distribution circuit as necessary. See appropriate wiring diagram in POWER DISTRIBUTION article in WIRING DIAGRAMS.
- Turn ignition switch to LOCK position. Measure resistance between ground and terminal No. 13 (Black/Yellow wire for non-flex fuel vehicles and Brown wire for flex fuel vehicles) at instrument cluster harness connector C251. See Figure . Also, measure resistance between ground and terminal No. 8 (Black/Yellow wire for non-flex fuel vehicles and Brown wire for flex fuel vehicles) at instrument cluster harness connector C250. See Figure . If both resistance readings are 3 ohms or less, go to next step. If either resistance reading is greater than 3 ohms, repair open in appropriate wire.
- Disconnect negative battery cable. Disconnect Powertrain Control Module (PCM) harness connector C191. Measure resistance between ground and terminal No. 8 (Tan/Yellow wire) at instrument cluster harness connector C251. If resistance is greater than 10 k/ohms, go to next step. If resistance is 10 k/ohms or less, repair short to ground in Tan/Yellow wire.
- Measure resistance in Tan/Yellow wire between terminal No. 8 at instrument cluster harness connector C251 and terminal No. 48 at PCM harness connector C191. See Figure and Fig 1 . If resistance is 5 ohms or less, go to next step. If resistance is greater than 5 ohms, repair open in Tan/Yellow wire.
- Connect negative battery cable. Turn ignition switch to RUN position. Measure voltage at terminal No. 8 (Tan/Yellow wire) at instrument cluster harness connector C251. If voltage does not exist, go to next step. If voltage exists, repair short to voltage in Tan/Yellow wire.
- Disconnect negative battery cable. Connect PCM harness connector C191. Connect negative battery cable. Start engine. Measure voltage at terminal No. 8 (Tan/Yellow wire) at instrument cluster harness connector C251. If voltage is 3-9 volts, replace tachometer. If voltage is not 3-9 volts, repair PCM concern. See appropriate SELF-DIAGNOSTIC article in ENGINE PERFORMANCE.