Error Code P0654 is defined as Engine RPM Output Circuit Malfunction. This is a generic trouble code, meaning it applies to all vehicles equipped with the OBD-II system, particularly those made since 1996 up to present. This includes models from, but not limited to, Buick, Cadillac, Chevrolet, Ford, GMC, Opel, Peugeot, etc. Specifications on the definition, troubleshooting, and repairs, of course, vary from make, model, and powertrain configuration.

When this code is stored, that means the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) or one of the other related controllers, has detected a discrepancy in the engine RPM (revolution per minute) output circuit.

Engine RPM provides RPM output signal to the instrument panel tachometer and other controllers. PCM receives this data from the camshaft and crankshaft sensors of the engine. This data is then used primarily for calculating and monitoring engine drivability then output to the tachometer, and other controllers (to which it’s instrumental).

If the PCM determines a problem in monitoring the engine RPM output circuit, Error Code Error Code P0654 will be stored and activate the Check Engine light.

Common Symptoms

In most cases, Check Engine light will be the only observable symptom for this code. But since it affects the engine RPM output circuit, it can also sometimes cause drivability and engine performance issues, such as:

  • No start condition
  • Erratic or harsh transmission shifting
  • ABS or TCS problems
  • Erratic tachometer

Other ABS or TCS codes may be stored as well.

Possible Causes

Defective circuitry is the most common cause of this code, which is corroded or loose wiring, broken or loose electrical connectors. Other common causes include:

  • Open or shorted instrument cluster harness
  • Defective tachometer
  • Defective instrument cluster
  • Bad crankshaft and camshaft sensor
  • Faulty PCM (rare)

How to Check

If there are other codes like VSS (vehicle speed sensor), engine RPM input codes, CMP (camshaft position) sensor, CKP (crankshaft position) sensor codes present other than the P0654, then they must be diagnosed and repaired first.

When trying to diagnose this code, refer to your information source or TSB (technical service bulletin); looks for signs and symptoms parallel to the stored code. Search for the year, make, model, and engine of your vehicle. If you can find the right TSB, then you may get the best diagnostic information about your problem.

You will need a diagnostic scanner, digital volt/ohmmeter, and an oscilloscope to diagnose this code accurately.

Next, connect your diagnostic scanner to the vehicle’s diagnostic connector, get all stored trouble codes too. You can write these codes down, including their freeze frame data, as this information can be of good help for you, especially if the code proves to be intermittent.

After recording this information, clear the codes and then take the vehicle for a test drive (if possible), until the code resets or the PCM enters readiness mode.

If the PCM enters readiness mode, that means the problem is intermittent. You may have to wait for the problem to get worse before you can successfully diagnose and repair. If the code resets on the other hand, then continue with the diagnosis.

Check all the related connectors and wirings, including the harnesses. Look for signs of damages. Harnesses that have been unplugged due to damage must be repaired or replaced.

If all the connectors and wirings look good, then use the vehicle information to know the connector pin-out charts, face views, component locators, wiring diagrams, and diagnostic flow charts of the vehicle.

As soon as you have the right information, use the DVOM and an oscilloscope to test the engine RPM at the right pin of the PCM connector. If there is no output signal, then you can suspect a defective PCM or a programming error in the PCM.

If there is an engine RPM output signal in the PCM connector, however, then you can test the corresponding circuit (as presented) at the instrument panel tachometer. If there’s no signal from the tachometer, then you may have an open circuit between the PCM and instrument panel. Repair or replace the circuit as necessary, and then retest.

How to Fix

Depending on your diagnosis, common repairs for this code include:

  • Repair or replacement of defective circuitry, such as broken electrical components, corroded wires, loose connectors, etc.
  • Repair or open or shorted instrument cluster harness
  • Replacement of defective instrument cluster
  • Replacement of defective tachometer
  • Replacement of bad CKP or CMP sensor
  • Replacement or reprogramming of PCM (rare)

If Error Code P0654 is stored, and the tachometer is operational, then you can suspect a defective or programming error in the PCM.

The most common misdiagnosis for this code is blaming the tachometer when the problem is actually in the PCM driver.