GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2007 🢒 Corvette 🢒 Diagnostic Navigation 🢒 Vehicle Diagnostic Information 🢒 Tachometer Inaccurate or Inoperative

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

Engine Speed Signal Circuit

P0654

P0654

P0654

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
    •  Engine Controls Schematics for the 6.0L engine
    •  Engine Controls Schematics for the 7.0L engine

Connector End View Reference

    •  Displays and Gages Connector End Views
    •  Engine Control Module Connector End Views for the 6.0L engine
    •  Engine Control Module Connector End Views for the 7.0L engine

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

    •  Scan Tool Data List
    •  Scan Tool Data List

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 Gage 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.
    2. ⇒If the tachometer does not perform the IPC Gage 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.
    4. ⇒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 C1 harness connector at the engine control module.
  5. Ignition ON, test for 9-11 volts between the engine speed signal circuit terminal 48 and ground.
    6. ⇒If less than 9 volts, test the engine speed signal circuit terminal 48 for a short to ground or an open/high resistance. If the circuit tests normal, replace the IPC.
    ⇒If greater than 11 volts, test the engine speed signal circuit terminal 48 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 after completing the diagnostic procedure.

Control Module References for the ECM, IPC and HUD replacement, setup and programming