P25BA: Regeneration Control Switch Circuit/Open

P25BA concerns the dash or panel switch with which the driver starts, or on some trucks blocks, a diesel particulate filter regeneration. The engine controller reads the switch as a discrete input and sets this code when the circuit is open or otherwise unusable, so a press no longer reaches it. Volvo describes a rocker of this kind: one half inhibits automatic regeneration below 40 km/h, the other starts a parked regeneration with the truck stationary, parking brake set, gearbox in neutral and engine warm. GM's L5P trucks with option FPF instead use the exhaust brake switch for the same job (bulletin 20-NA-203). No manufacturer documents P25BA publicly. Automatic regeneration while driving continues, but a requested parked regeneration cannot be started and soot can build up.

Symptoms

• Parked regeneration cannot be started when the cluster asks for it
• Filter or regeneration warning lamp stays on longer than usual
• Check engine lamp

Most likely causes

• Switch connector loose or unplugged behind the dash
• Broken signal or reference wire to the switch
• Internal open circuit in the regeneration switch

What to check, in order

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

1. Read the soot load and differential pressure with a scanner
2. Check the continuity of the wire between the component and the control module.
3. Check the differential pressure sensor's hoses
4. Check the temperatures before and after the filter
5. Fix any fuel injection or EGR codes before regenerating
6. Perform a regeneration while driving or at a repair shop when the diagnosis allows it

Good to know

• Repair difficulty: easy
• It affects emissions.

What each character of P25BA means

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

Frequently asked questions

Can I keep driving with code P25BA?

If the light is on steadily, take a highway drive or go to a repair shop soon. If the car is in limp mode or the light is flashing, do not push the engine.

What causes code P25BA?

The most common causes are: switch connector loose or unplugged behind the dash; broken signal or reference wire to the switch; internal open circuit in the regeneration switch.

Related codes

• P25BBRegeneration Control Switch Circuit Low
• P25BCRegeneration Control Switch Circuit High
• P2459Diesel Particulate Filter Regeneration Frequency

Sources

• stpi.it.volvo.com: DRC AMII Eng 02 333484271
• static.nhtsa.gov: MC 10231499 0001
• law.cornell.edu: 13 CCR 1968.2

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.