Electrical and sensors

P0654 — Engine RPM Output Circuit Malfunction

Severity: low Safe to drive

What P0654 means

The engine control module generates an engine speed output signal and sends it to the tachometer in the instrument cluster, and sometimes to other devices. P0654 sets when the ECM sees that the voltage or waveform on this output does not match what it commands, for example an open circuit or a short to ground or voltage. The engine itself usually runs normally; only the RPM signal is affected.

Symptoms

  • Tachometer not working or jumping erratically
  • Check engine light on
  • Tachometer shows wrong RPM
  • Accessories that use the RPM signal not working
  • Engine usually starts and runs normally

Possible causes

  1. Failed output driver inside the ECM
  2. Open or shorted tach signal wire
  3. Faulty instrument cluster or its tach circuit
  4. Aftermarket device (alarm, remote start, shift light, tuner) tapped into the tach wire
  5. Corroded or damaged connector at the ECM or cluster
  6. Internal ECM failure

How to diagnose

  1. Scan for codes and freeze frame data, then compare scan tool RPM with the tach reading
  2. Look for aftermarket devices connected to the tach signal wire and unplug them as a test
  3. Inspect the harness and connectors between the ECM and the cluster for damage, corrosion and chafing
  4. Using the wiring diagram, test the tach signal wire for opens and shorts to ground or voltage
  5. Check the signal at the ECM output with a scope or meter while the engine runs
  6. Verify ECM power and ground circuits
  7. Test the instrument cluster and tach function (cluster self-test or scan tool output test if supported)
  8. If wiring and loads are fine but there is no signal, suspect the ECM

Common fixes

  • Remove or correctly rewire the aftermarket device
  • Repair the damaged wire or replace the connector or terminal
  • Repair or replace the instrument cluster
  • Repair, reflash or replace the ECM and program it as required
  • Clear the code and confirm it does not return

Questions and answers

What does P0654 mean?

The ECM found a problem in the output circuit that sends engine speed to the tachometer or other devices. The usual culprits are wiring, aftermarket equipment or the ECM itself.

Can I drive with code P0654?

Usually yes, because the engine normally keeps running fine. Still, get it checked soon: you lose a reliable tach, and a failing ECM could cause other problems.

Can an alarm or remote starter cause P0654?

Yes. If an alarm, remote start or similar device is spliced into the RPM wire, it can distort the signal. Disconnect it and see whether the code comes back.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.