Powertrain, generic (extended)

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

Check engine lightOn

EmissionsRelevant

Drive cycleRequired

Limp modeNo

An exhaust heat exchanger moves exhaust heat into the coolant after a cold start; a flap (bypass valve A) decides whether gas flows through it or around it, and a position sensor reports where the flap is. P25D6 targets the end-stop values of that sensor: at the fully open and fully closed stops the reading must sit inside a learned or calibrated window. If a stop is no longer reached, or the stop value has shifted, the code is set. No manufacturer documents P25D6 publicly; the B-side twin is P23A8. The closest documented case is Ford's general valve A position sensor performance code P2C23 on full hybrids (F-150, Explorer, Escape, Maverick), where SSM 52543 first checks the exhaust coolant temperature sensor connectors and SSM 53003 replaces a worn actuator. Driving usually feels normal; warm-up may slow.

Likely causes

Carbon build-up or a bent flap stopping short of its end stop

Worn valve actuator or linkage play

Position sensor shifted on its mount or drifting

End stops not relearned after parts replacement

Symptoms

Check engine lamp on without noticeable driving change
Slower engine warm-up or weaker cabin heat in winter

Repair estimate

DifficultyHardWorkshop job

Parts and labour€150–1,800

Time1–5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

exhaust heat exchangerbypass valve actuatorposition sensor

References: en.wikipedia.org, static.nhtsa.gov, static.nhtsa.gov, law.cornell.edu.