PCM Controlled Tachometer Diagnosis

Circuit Description

The Ignition Control (IC) Module supplies the tachometer signal to the Instrument Cluster. When the vehicle is started the 7X CKP sensor produces a signal that is received by the IC Module, the module then generates a reference pulse known as the 3X Reference the module sends this reference signal to the PCM to perform other ignition functions, and to the Instrument Cluster for the tachometer signal.

Diagnostic Aids

Check for the following conditions:

^ Poor connection at the PCM or instrument cluster. Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. Refer to Diagrams.
^ Damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, disconnect the PCM, turn the ignition ON and observe voltmeter connected to the tachometer control circuit at the PCM harness connector while moving connectors and wiring harnesses related to the tachometer control circuit. A change in voltage will indicate the location of the fault.

Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table:

8. This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.