For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Engine RPM Signal | 1 | 1 | 1 | --
Tachometer Malfunction

### Circuit/System Description

The engine control module (ECM) creates the engine speed signal. The engine speed is sent to the IPC over a discreet wire from the ECM. The instrument panel cluster (IPC) converts the signal to a tachometer position indicating the engine speed.

### Diagnostic Aids

Before attempting to diagnose a tachometer malfunction diagnose any ECM DTCs or driveability concerns.

### Reference Information

#### Schematic Reference

Instrument Cluster Schematics

#### Connector End View Reference

Displays and Gages Connector End Views

#### Description and Operation

Instrument Panel Description

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

Start the engine with the scan tool installed. Verify that the Engine Speed parameter in the ECM IPC Data list varies with the actual engine RPM.

⇒ | If the parameter displayed is not the correct value replace the ECM.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connectors at the ECM and IPC.
2. Test the engine speed signal circuit for infinite resistance between the ECM connector terminal and ground.

⇒ | If not the specified value, repair the signal circuit for a short to ground.

3. Test the engine speed signal circuit for less than 2 Ω between the ECM connector terminal and the IPC connector terminal.

⇒ | If not the specified value, test the signal circuit for a short to voltage or an open/high resistance.

4. If all circuits test normal, replace the IPC.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for IPC or ECM replacement, setup and programming