PCM Controlled Tachometer Diagnosis

Refer to Engine Controls Schematic EBCM, Generator, PCM, Tachometer.

Diagnostic Chart:

CIRCUIT DESCRIPTION
The PCM controls the pulse frequency in relationship to engine RPM, and sends the information Class II to the Instrument Cluster.

DIAGNOSTIC AIDS
Refer to A Diagnostic Starting Point - Instrument Panel, Gauges and Console in Instrument Panel,Gauges and Console for additional diagnostic information. Diagnostic Starting Point

Inspect for the following conditions:

IMPORTANT: Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.

^ Poor terminal connection-Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Use a corresponding mating terminal to test for proper tension.
^ Damaged harness-Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault.
^ PCM and engine grounds for clean and secure connections

If the DTC is determined to be intermittent, reviewing the Failure Records can be useful in determining when the DTC was last set.