• | Perform the Diagnostic System Check - Vehicle prior to using the diagnostic procedure. |
• | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
• | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
---|---|---|---|---|
Engine Speed Signal | P0654 | P0654 | P0654 | -- |
1. Tachometer Inaccurate or Inoperative |
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 IPC. The ECM monitors the voltage at the engine speed signal circuit to determine when the voltage is out of the normal operating range.
• | The engine speed is greater than 400 RPM. |
• | The ignition voltage is greater than 6 volts, but less than 18 volts. |
• | The ECM detects that the commanded state of the driver and the actual state of the signal circuit do not match. |
• | The above condition exists for a minimum of 5 seconds. |
• | The ECM stores the DTC information in memory when the diagnostic test runs and fails. |
• | The malfunction indicator lamp (MIL) will not illuminate. |
• | The ECM records the operating conditions at the time when the diagnostic test fails. The ECM stores this information in the Failure Records. |
• | The DTC becomes history when the conditions for setting the DTC are no longer present. |
• | A history DTC is cleared after 40 consecutive malfunction-free warm-up cycles. |
Instrument Cluster Description and Operation
Control Module References for scan tool information
⇒ | If no RPM reading is present, test the signal circuit for an open/high resistance, a short to voltage, or a short to ground. If the circuit tests normal, replace the instrument panel cluster (IPC). |
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control Module References for the ECM and IPC replacement, setup, and programming