Tachometer Inaccurate or Inoperative

TACHOMETER INACCURATE OR INOPERATIVE

DIAGNOSTIC FAULT INFORMATION

IMPORTANT: Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Testing and Inspection

CIRCUIT/SYSTEM DESCRIPTION
The instrument panel cluster (IPC) displays the engine speed based on the engine speed data from the engine control module (ECM) or the powertrain control module (PCM). The ECM/PCM converts the data from the engine speed sensor to a 2 pulses/engine revolution signal. The ECM/PCM sends a GMLAN message to the IPC indicating the engine speed. The IPC displays the engine speed based on the GMLAN serial data message from the ECM/PCM.

CIRCUIT/SYSTEM TESTING
1. Install a scan tool.
2. Turn ON the ignition, with the engine OFF.
3. With the scan tool, under Special Functions, perform the tachometer gage sweep test.
- If the tachometer gage does not sweep from its low to high position, replace the instrument panel cluster.