What it means
Same as P04D3 with the signal in plausible range yet not matching expected behaviour - e.g. activation request without driver input or no response after a request.
At a glance
- Usually lights the check-engine light
How it works
The exhaust-brake input tells the control module when the driver requests engine braking. This code sets when the signal is electrically plausible but its behavior does not match the expected request, such as changing without driver input or failing to track the control.
Common causes
Most likely first.
- Faulty or misadjusted exhaust-brake switch
- Input signal inconsistent with driver request
- Intermittent wiring or connector fault
Symptoms
- Exhaust brake may engage unexpectedly or fail to engage
- Exhaust-braking response may be inconsistent
How to diagnose it
- Review freeze-frame data and live input status, comparing the exhaust-brake request with each operation of the driver control.
- Check whether the signal changes consistently with the switch or pedal input and whether it remains inactive when the control is released.
- Inspect the switch adjustment, connector fit, and nearby wiring for looseness, corrosion, chafing, or movement that could distort the request.
- Use the wiring diagram to test the input signal and circuit continuity while operating the control and gently moving the harness.
- If the electrical input follows the control correctly, check related exhaust-brake status or vehicle-bus data against the manufacturer’s diagnostic information.
Common fixes
- Correct the adjustment of a misaligned exhaust-brake switch.
- Secure a loose connector or repair intermittent wiring at the input circuit.
- Replace a faulty exhaust-brake switch or input sensor that does not track driver operation.
- Repair corroded terminals or damaged wiring causing an implausible request.
Can I keep driving?
Drive cautiously because the exhaust brake could fail to engage or activate unexpectedly. Avoid relying on it to control speed on descents, and have the input fault checked before operating in demanding terrain.
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.