Tachometer Inaccurate or Inoperative
Tachometer Inaccurate or Inoperative
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this 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.
Diagnostic Fault Information
Circuit/System Description
The engine control module (ECM) creates the engine speed signal by pulsing the engine speed signal circuit to ground at a rate of 2 pulses per engine revolution. The IPC converts the 2 pulses per engine revolution signal to a tachometer position indicating the engine speed. The engine speed is sent to the instrument panel cluster (IPC) over a discreet wire from the ECM. The tachometer signal is pulled up to B+ in the instrument panel cluster (IPC). The ECM monitors the voltage at the engine speed signal circuit to determine when the voltage is out of the normal operating range.
Reference Information
Schematic Reference
Instrument Cluster Schematics (Instrument Cluster Schematics)
Connector End View Reference
Component Connector End Views (Connector Views)
Description and Operation
Instrument Cluster Description and Operation (Instrument Cluster)
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 (Programming and Relearning) for scan tool information
Circuit/System Verification
Start the engine with the scan tool installed. Verify that the tachometer display matches the scan tool Engine Speed parameter in the ECM Engine Data List.
Circuit/System Testing
1. Ignition ON, with the scan tool installed, perform the IPC Gauge Sweep Test in the IPC Output Controls. Verify the tachometer dial moves from the minimum to the maximum position and back to the tachometer minimum position.
• If the tachometer does not perform the IPC Gauge Sweep Test, replace the IPC.
2. Ignition OFF, disconnect the harness connector at the head-up display (HUD).
3. Start the engine and verify that the tachometer value does not match the scan tool Engine Speed parameter in the ECM Engine Data List.
• If the tachometer matches the scan tool Engine Speed parameter, test the engine speed signal circuit terminal 4 for a short to voltage, a short to ground or an open/high resistance. If the circuit tests normal, replace the HUD.
4. Ignition OFF, disconnect the X1 harness connector at the ECM.
5. Ignition ON, test for 9-11 volts between the engine speed signal circuit terminal 48 and ground.
• If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the IPC.
• If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the IPC.
6. If all circuits test normal, test or replace the ECM.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
Control Module References (Programming and Relearning) for the ECM, IPC and HUD replacement, setup and programming