P2BA7
NOx Exceedence - Empty Reagent Tank
Diesel emissions (SCR/DEF)
Generic OBD-II
High
What it means
P2BA7 is a diesel SCR code meaning NOx emissions have exceeded the limit because the reagent (DEF/AdBlue) tank is empty. To stay emissions-legal the vehicle warns you, then reduces power and may refuse to restart until you refill. The fix is almost always simply topping up diesel exhaust fluid, so act on it before the countdown strands you.
High
Can I keep driving? Limited and time-critical — with the DEF/reagent tank empty the vehicle will warn, then reduce power (derate) and may refuse to restart. Refill diesel exhaust fluid immediately.
Common symptoms
What you'll notice
- DEF/AdBlue warning light or message with a distance/restart countdown
- Reduced engine power (derate) and capped speed
- Vehicle may refuse to restart once the countdown expires
- Check-engine light on
Common causes
Most likely first
- Diesel exhaust fluid (DEF/AdBlue) reagent tank is emptyLikely
- DEF quality poor or diluted (water added, wrong fluid)Common
- Faulty DEF level sensor reading emptyCommon
- DEF pump, injector, or lines blocked/frozen so reagent is not dosedLess often
- NOx sensor or SCR fault causing a false exceedance (less common)Less often
How to diagnose & fix
Work through it in order
- Refill the DEF/reagent tank with fresh, correct-spec diesel exhaust fluid first.
- Cycle the ignition and allow the system to re-prime and re-check the level; the derate should clear.
- If it stays empty after filling, check the DEF level sensor and for leaks or a blocked pickup.
- Test the DEF pump/injector dosing and the NOx sensors if the exceedance persists.
- Clear the code (or let it self-clear) and confirm normal power returns after a drive cycle.
FAQ
Quick answers
Is it safe to drive with P2BA7?+
Only until you can refill. The system deliberately reduces power and can block a restart to force a DEF refill. Top up the reagent as soon as possible.
Can I just clear P2BA7?+
No. Clearing it does nothing if the tank is empty — refill DEF first. The code and derate lift once the system detects proper reagent.
Related codes
Often seen with P2BA7
Read & clear P2BA7 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX