P25A1: Turbocharger B Boost Control Position At High Limit

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.

Symptoms

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

Most 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

What to check, in order

Start with the simplest. You can tick off each step.

1. Check the hoses, clamps, and intercooler
2. Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
3. Compare commanded and actual pressure in live data
4. Check the actuator's movement
5. Check the vacuum hoses and the solenoid valve
6. Check the oil and the turbo shaft play before replacing it

Good to know

• Repair difficulty: medium
• It can trigger limp mode.
• It affects emissions.

What each character of P25A1 means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 5: Speed and idle
• A1: Specific fault in that system

Frequently asked questions

Can I keep driving with code P25A1?

Drive without demanding power and go to a repair shop soon. If you see a lot of blue smoke or hear a metallic noise, shut off the engine.

What causes code P25A1?

The most common causes are: wastegate or vanes of charger B stuck toward closed; blocked, leaking or misrouted control line of actuator B; boost pressure sensor giving wrong values.

Related codes

• P25A0Turbocharger B Boost Control Position At Low Limit
• P259FTurbocharger A Boost Control Position At High Limit
• P259BTurbocharger Boost Control Position Sensor B Performance - Stuck High

Sources

• law.cornell.edu: 13 CCR 1968.2
• fordservicecontent.com: obd summary diesel 2023

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.