P25BBRegeneration Control Switch Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- P25BB reports that the regeneration switch input reads a low level the switch itself cannot produce. Depending on the wiring, this points to a short to ground in the harness, a contact that is permanently closed to ground or a damaged switch module. On a ground-switching design such a fault would look like a button held down all the time, so the controller can no longer tell a genuine request from the defect and has reason to disregard the input. Regeneration switches are typical on vocational trucks, buses and chassis cabs that idle a lot and have to clean the filter while parked; the US Forest Service explains the procedure for its own diesel fleet. No manufacturer documents P25BB publicly. Its sibling P25BC covers the high side, P25BA an open circuit.
- What you may notice
- Regeneration switch has no effect
- Parked regeneration may be unavailable when soot load is high
- Check engine lamp
- Likely causes
- LikelySwitch signal wire shorted to ground
- PossibleSwitch contact stuck closed
- RareSwitch panel damaged by liquid or impact
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Easy · Often possible to do yourself.Typical cost: €40 – €300
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.