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Tahoe / Yukon Service Manual

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. Circuit/System Description The engine control module creates the engine speed signal by pulsing the engine speed signal circuit to ground at a rate proportional to engine revolution speed. The Instrument Panel Cluster Control Module converts the engine revolution signal to a tachometer position indicating the engine speed. The engine speed is sent to the Instrument Panel Cluster Control Module over a discreet wire from the engine control module. The tachometer signal is pulled up to B+ in the Instrument Panel Cluster Control Module. The engine control module 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 Connector End View Reference Master Electrical Component List Description and Operation Instrument Cluster Description and Operation 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 Testing

  1. Ignition ON/Vehicle in Service Mode.
  2. Verify the tachometer moves from the minimum to the maximum position and back to the minimum position when performing the Instrument Panel Cluster Control Module Gauge Sweep Test with the scan tool. ⇒ If tachometer does not sweep Replace the P16 Instrument Panel Cluster Control Module. ⇓ If speedometer sweeps properly
  3. Engine Running.
  4. Verify the scan tool parameters listed below do not display Malfunction: Camshaft Position Signal Output Circuit Low Voltage Test Status Camshaft Position Signal Output Circuit Open Test Status Camshaft Position Signal Output Circuit High Voltage Test Status ⇒ If Malfunction is not displayed Replace the P16 Instrument Panel Cluster Control Module. ⇓ If Malfunction is displayed
  5. Ignition OFF, disconnect the X1 harness connector at the P16 Instrument Panel Cluster Control Module, engine Running.
  6. Test for 15–30 Hz DC between the signal circuit terminal 22 and ground. ⇒ If not between 15–30 Hz DC 6.1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module. 6.2. Test for less than 1 V between the signal circuit and ground. ⇒ If 1 V or greater, repair the short to voltage on the circuit. ⇓ If less than 1 V 6.3. Test for infinite resistance between the signal circuit and ground. ⇒ If less than infinite resistance, repair the short to ground on the circuit. ⇓ If infinite resistance. 6.4. Test for less than 2 Ω in the signal circuit end to end. ⇒ If 2 Ω or greater, repair the open/high resistance in the circuit. ⇒ If less than 2 Ω, replace the K20 Engine Control Module. ⇓ If between 15–30 Hz DC
  7. Replace the P16 Instrument Panel Cluster Control Module. Repair Instructions Perform the Diagnostic Repair Verification after completing the repair. Control Module References for control module replacement, programming, and setup