Tachometer Inaccurate or Inoperative

Tachometer Inaccurate or Inoperative

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using the diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.

Circuit Description

The instrument panel cluster (IPC) receives the engine speed information from the engine control module (ECM)/powertrain control module (PCM) through the engine speed signal circuit. The ECM/PCM converts the data from the engine speed sensor to a (2 pulses)/(engine revolution) signal. The ECM/PCM also sends a class 2 message to the IPC indicating the engine speed.

Reference Information
Schematic Reference

* Instrument Cluster Schematics (Instrument Cluster Schematics)
* Engine Controls Schematics ([1][2]Electrical Diagrams) for the 4.2L engine
* Engine Controls Schematics ([1][2]Electrical Diagrams) for the 4.8L, 5.3L, 6.0L, 6.2L and 7.0L engines

Connector End View Reference

Component Connector End Views (Component Connector End Views)
Description and Operation

* Instrument Cluster Description and Operation (Description and Operation)
* Engine Control Module Description (Engine Control Module Description) for the 4.2L engine
* Engine Control Module Description (Engine Control Module Description) for the 4.8L, 5.3L, 6.0L, 6.2L and 7.0L engines

Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

Scan Tool Reference

Control Module References (Control Module References) for scan tool information

Circuit/System Testing

1. Engine ON, verify the scan tool Engine Speed parameter matches the tachometer display.

• If the Engine Speed parameter does not match the tachometer display, test the signal circuit terminal A12 for an open/high resistance.

2. If the circuit tests normal, replace the IPC.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

Control Module References (Control Module References) for the IPC replacement, setup, and programming