Speedometer and/or Odometer Inaccurate or Inoperative 4.2L Engine
Diagnostic Instructions
Circuit Description
The engine control module (ECM) creates the vehicle speed signal by pulsing the vehicle speed signal circuit to ground at a rate of 4KPPM. The instrument panel cluster (IPC) converts the 4KPPM vehicle speed signal to a speedometer position to indicate
the vehicle speed. The IPC also receives from the ECM a serial data message indicating the vehicle speed. The IPC uses the serial data vehicle speed information from the ECM for diagnostics purposes. The ECM monitors the voltage on the vehicle speed signal circuit
and determines when the voltage is out of the normal operating range.
Reference Information
Schematic Reference
Instrument Cluster Schematics
Connector End View Reference
Component Connector End Views
Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
Important: The drive wheels of the vehicle must be raised and the transmission must be placed in drive or first gear. Refer to
Lifting and Jacking the Vehicle.
| • | Ignition ON, perform the speedometer sweep test with the scan tool. Verify that the speedometer gage sweeps from its low to high position. |
| ⇒ | If the speedometer gage does not sweep from its low to high position, replace the IPC. |
| • | Start the engine with the scan tool installed, the vehicle drive wheels raised and the transmission placed in drive or the first gear. Verify the speedometer display matches the scan tool Vehicle Speed parameter in the ECM Engine Data List. |
Circuit/System Testing
- Ignition OFF, disconnect the X1 harness connector at the ECM. Install a signal generator and instrument panel tester between the vehicle speed signal circuit terminal 39 and ground.
- Ignition ON, set the signal generator to generate a speedometer signal. Verify that the vehicle speedometer indicates a reading.
| ⇒ | If no speedometer reading is present, test the signal circuit for a short to voltage, a short to ground or an open/high resistance. If the circuit tests normal, replace the instrument panel cluster (IPC). |
- 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 IPC replacement, setup, and programming
Speedometer and/or Odometer Inaccurate or Inoperative 4.8L, 5.3L, 6.0L, 6.2L, 7.0L Engines
Diagnostic Instructions
Circuit Description
The instrument panel cluster (IPC) receives the vehicle speed information from the engine control module (ECM) through the vehicle speed signal circuit. The ECM converts the data from the vehicle speed sensor to a 4,000 pulses/mile signal. The ECM also
sends a serial data message to the IPC indicating the vehicle speed.
Reference Information
Schematic Reference
Connector End View Reference
Component Connector End Views
Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Testing
- Ignition ON, perform the segments test with the scan tool.
| ⇒ | If not all of the segments illuminate, replace the IPC. |
- Raise the vehicle drive wheels. Refer to
Lifting and Jacking the Vehicle.
- Engine ON, transmission in drive, verify the scan tool Vehicle Speed Sensor parameter matches the speedometer display.
| ⇒ | If the Vehicle Speed Sensor parameter does not match the speedometer display, test both the vehicle speed signal circuit terminal B9 for an open/high resistance and the high-front signal circuit terminal 16 at the transmission control module
(TCM) for an open/high resistance, short to voltage, or short to ground. |
- If the circuits test normal, test or replace the IPC.
Repair Instructions
Perform the
Diagnostic Repair Verification after completing the diagnostic procedure.
Control Module References for the IPC replacement, setup, and programming
