P25BB: Regeneration Control Switch Circuit Low
Regeneration control switch input reads stuck low — short to ground or stuck-closed contact. The ECM may see a constant regen request which it cannot service while the vehicle is moving.
What P25BB means
P25BB is a generic OBD-II powertrain code in the speed, idle & cruise group. In plain English: the computer sees a voltage on that circuit that is lower than it should ever be — often a short to ground, an open, or a failed sensor.
- Check engine light
- Usually on
- Emissions-related
- Yes — can fail inspection
- Limp mode possible
- Not typical
- Drive cycle to clear
- Not required
Get it fixed
Post this code once and get quotes from local mechanics. Free to post.
Makes the repair and parts links below specific to your car. Kept in this browser only.
Common causes
- 01Switch wire shorted to groundMost likely
- 02Connector pins corroded - high contact resistanceLess likely
- 03Harness chafing through insulationLess likely
Can I drive with P25BB?
Usually yes, for a short time.
The car will often drive normally, but get it diagnosed soon. Left alone it can raise fuel use and emissions and will fail an OBD inspection. If you notice rough running, warning lights flashing, overheating or a burning smell, stop driving.
Why we rate it moderate
- Turns on the check engine light
- Emissions-related: will usually fail an OBD inspection
Severity is our rule-based rating from the code’s flags in OBDex and the system it affects, not an inspection of your car. If the check engine light is flashing, or you notice overheating, low oil pressure, or brake or steering problems, stop driving and get help.
How to diagnose P25BB
- 1
Confirm the code and save freeze-frame data
Read the codes with an OBD-II scan tool and note every code, not just P25BB. Save the freeze-frame data (speed, load, temperature when the fault set) before clearing anything; it tells you when the fault happens.
- 2
Check for related codes first
Look for P25BA. Related codes often share a cause; a circuit or sensor code usually needs fixing before a performance code like this one.
- 3
Test the circuit
Inspect the wiring and connector at the regen request switch for damage, corrosion or chafing. With a multimeter, check supply voltage, ground and signal against the specifications in the service manual for your vehicle.
- 4
Test the likely causes in order
Start with the most likely cause and work down: Switch wire shorted to ground; connector pins corroded - high contact resistance; harness chafing through insulation. Test before replacing parts.
- 5
Check for recalls and service bulletins
Look up recalls for your exact vehicle with its VIN, and ask a dealer about technical service bulletins (TSBs). Manufacturers sometimes issue software updates or extended warranties for known faults.
- 6
Clear the code and verify the repair
After the repair, clear the code and drive the car under the conditions in the freeze-frame data to confirm it does not return.
P25BB repair cost estimate
Estimate, not a quote. Labor times are typical ranges for this code from OBDex, and $125/hr is an assumed rate. Shop rates and labor times vary by vehicle and region. Diagnosis time may be billed separately.
- DIY difficulty
- Moderate
- Good DIY job?
- Yes, with a scan tool
Needs a scan tool and some experience with testing.
Parts and systems involved
- Regen request switch
P25BB FAQ
What does P25BB mean?
P25BB means “Regeneration Control Switch Circuit Low”. Regeneration control switch input reads stuck low — short to ground or stuck-closed contact. The ECM may see a constant regen request which it cannot service while the vehicle is moving.
Is P25BB serious? Can I keep driving?
We rate P25BB as moderate severity. Usually yes, for a short time. The car will often drive normally, but get it diagnosed soon. Left alone it can raise fuel use and emissions and will fail an OBD inspection. If you notice rough running, warning lights flashing, overheating or a burning smell, stop driving.
What causes P25BB?
The most common causes, from most to least likely: Switch wire shorted to ground; Connector pins corroded - high contact resistance; Harness chafing through insulation. Test before replacing parts, because several causes can set the same code.
How much does it cost to fix P25BB?
Typical labor is about $40–$190 at an assumed $125/hour shop rate, plus parts. That is an estimate, not a quote: labor times and rates vary by vehicle and region, and diagnosis may be billed separately.
Can I fix P25BB myself?
DIY difficulty is moderate. Many owners can handle it with a scan tool, a multimeter and basic hand tools. Always confirm the cause before buying parts.
Will P25BB clear itself?
If the fault was intermittent, the warning may go off once the computer stops seeing it, but the code stays in memory. Fix the cause; clearing the code alone doesn’t repair anything.