What it means
The engine RPM signal output that the ECU sends to other modules (tachometer, transmission, ABS) has an open circuit.
At a glance
- Usually lights the check-engine light
How it works
The engine control module provides an RPM output signal that other vehicle systems, such as the instrument cluster or transmission controller, may use. P0654 sets when the module detects an open or missing path in that output circuit, so receiving modules may not get a usable engine-speed signal.
Common causes
Most likely first.
- Open in output wiring
- Pin pushed back out of connector body
- Cracked solder joint inside the module or sensor
Symptoms
- Check engine light on
- Possible limp mode or no-start
- Multiple follow-up faults across modules
- Reset/relearn may be needed after repair
How to diagnose it
- Read freeze-frame data and scan all modules for communication or engine-speed-related codes to see which systems lost the RPM signal.
- Compare engine speed shown by the engine control module with the tachometer and other modules' live data while the engine is running.
- Inspect the RPM output wire, connectors, and related grounds for damage, corrosion, loose plugs, or pins pushed back into the connector body.
- Check the output circuit for continuity and shorts using the wiring diagram, following the manufacturer's test procedure and specification.
- If the external circuit checks out, test the receiving module input and the control module output before concluding that a module has failed.
Common fixes
- Repair an open or damaged RPM output wire.
- Reseat or repair a connector with a loose or pushed-back pin.
- Repair a poor ground or connection identified during circuit testing.
- Repair or replace a failed module only after its output and wiring have been verified.
Can I keep driving?
The engine may still run, but the tachometer or systems that depend on the RPM signal may not work correctly, and shifting or stability functions can be affected. Avoid driving if related transmission or safety-system warnings appear, and arrange repair soon.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.