Powertrain, generic (extended)

P25A1 Turbocharger B Boost Control Position At High Limit

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P25A1 is set when the boost control for turbocharger B is pinned at its upper limit and still cannot bring pressure down to the requested value, so the second charger overshoots. Like P25A0 it is limited to engines with two individually controlled chargers, and no manufacturer has published its own criteria for P25A1. CARB 13 CCR 1968.2 asks the OBD system to detect boost control that has exhausted its authority as well as boost that climbs above the commanded level. Ford's overboost monitor for turbocharger A (P259F) gives a sense of scale: 120 kPa above target for about 10 s on the 6.7 L diesel. A wastegate or vane mechanism stuck toward closed, a blocked or misrouted control line, or false sensor readings are typical. Engines usually limit power to protect the turbo.

Likely causes

Wastegate or vanes of charger B stuck toward closed
Blocked, leaking or misrouted control line of actuator B
Boost pressure sensor giving wrong values

Symptoms

  • Engine warning lamp on
  • Power cut-out at high load

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–2,500
Time0.5–6 h

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

Parts involved

turbo actuator bwastegate

Related codes

P25A0P259FP259B

References: law.cornell.edu, fordservicecontent.com.