P25D6: Exhaust Heat Exchanger Exhaust Bypass Valve Position Sensor Stop Performance

What it means

During self-calibration of the exhaust heat exchanger bypass valve A, the position sensor never reached the expected mechanical stop. The controller cannot zero the position reference, so commanded openings will be inaccurate.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test

How it works

The exhaust heat exchanger bypass valve directs exhaust flow through or around the heat exchanger, and its position sensor reports the valve's movement to the control module. During calibration, P25D6 sets when the sensor does not register the valve's expected stop, so the controller cannot establish a reliable position reference.

Common causes

Most likely first.

1. Soot or carbon deposits prevent valve from reaching the stop
2. Worn linkage between actuator and valve flap
3. Position sensor not aligned with valve shaft

Symptoms

• Reduced engine power
• Check-engine light may illuminate

How to diagnose it

1. Save freeze-frame data and check for other exhaust heat exchanger or bypass-valve codes that may help explain the calibration failure.
2. With the engine cool, inspect the bypass valve and surrounding area for soot or carbon that could obstruct its travel.
3. Check the actuator-to-valve linkage for looseness, wear, or disconnection that could prevent the flap reaching its stop.
4. Inspect whether the position sensor is properly aligned with the valve shaft, following the manufacturer's procedure.
5. If the valve moves freely and linkage alignment is sound, use the manufacturer's procedure to check sensor readings during calibration.

Common fixes

• Remove deposits that are preventing the bypass valve from reaching its stop, using the manufacturer's service procedure.
• Repair or replace worn or disconnected actuator linkage.
• Realign the position sensor with the valve shaft as specified by the manufacturer.
• Replace the position sensor or actuator only if testing identifies it as faulty.

Can I keep driving?

Reduced power may make merging or overtaking difficult, so avoid demanding driving and arrange a prompt diagnosis. If power drops sharply or the engine runs abnormally, stop somewhere safe.