What to do about a P2BAD fault code
Left alone, P2BAD usually ends in a no-restart countdown on Euro 6 vehicles, so it's one to get read soon. It means NOx from the exhaust is too high and the engine computer can't pin down why, which is where a proper diagnostic at your home or workplace comes in.
Can you keep using it with P2BAD?
Fine for now
If there's no countdown showing and the vehicle feels normal, you can usually keep using it for a few days while you book a check.
Get it booked this week
Once a countdown appears, get it diagnosed this week. P2BAD rarely clears itself, and the counter keeps falling with each trip.
Stop and call us
Call straight away if the countdown is in low figures. If it reaches zero, the engine won't restart once it's switched off, wherever you happen to be.
Signs that go with P2BAD
- An AdBlue, emissions or "anti-pollution" warning on the dash
- A countdown to no-restart
- Other AdBlue or NOx sensor codes stored with it
- Little or no change in performance
What P2BAD means
The official definition is NOx exceedance, root cause unknown. The NOx sensors show more nitrogen oxides leaving the exhaust than the limit allows, and the ECU's own checks haven't been able to blame one part. That makes it a "something is wrong" code that needs the other stored codes and live data to explain it.
Common causes
A failing NOx sensor
A sensor reading high, or a slow one, can make NOx look too high when it isn't.
AdBlue dosing problems
A crystallised injector, weak pump or poor-quality fluid means not enough AdBlue reaches the catalyst.
An EGR fault
If the EGR valve isn't recirculating enough gas, the engine makes more NOx than the AdBlue system can deal with.
A worn SCR catalyst
An old or contaminated catalyst can't convert NOx as well, even with healthy dosing.
What to do right now
- Note the countdown figure and keep an eye on how fast it's falling.
- Check the AdBlue level and top up from a fresh, sealed container if it's low.
- Plan your stops. If the counter is low, finish the journey somewhere you can leave the vehicle for a visit.
- Don't keep clearing the code. It won't reset the countdown on most vehicles and loses useful data.
- Book a check and give us the full code and any others on your reader.
How we sort P2BAD where the vehicle is parked
We read every stored code, both NOx sensors, AdBlue dosing and EGR data to find the real cause behind P2BAD. Diagnostics is £100 + VAT. We don't repair or replace AdBlue pumps, heaters, tanks or NOx sensors, so any repair goes to a dealer or SCR specialist with our findings.
The AdBlue delete (£330 + VAT) is the other option. If the countdown has run out and the vehicle won't start, tell us when you book.
Reviews
Related NOx exceedance codes
These sit in the same family as P2BAD, but name a cause. We read and diagnose them the same way.
- P2BA9 is listed as NOx exceedance, insufficient reagent quality, meaning the AdBlue itself is suspected of being too weak or contaminated.
- P2BAC is listed as NOx exceedance, deactivation of EGR, where high NOx is put down to the EGR system being switched off or not working.
- P2BAE is listed as NOx exceedance, NOx control monitoring system, a general NOx fault whose exact meaning can vary by make.
Will P2BAD put the car into limp mode?
Some vehicles reduce power, but the bigger risk is the no-restart countdown. Once that runs out, the engine won't start again after switching off.
How long can I leave P2BAD before it gets worse?
Only as long as the countdown allows. Book as soon as a counter appears, rather than waiting for low figures.
Can P2BAD damage the catalyst?
Not by itself. A dosing fault that leaves crystals in the exhaust can block the injector and catalyst over time, though.
Will my car pass its MOT with P2BAD showing?
No. The lit engine light is an MOT fail, and higher NOx is exactly what the code is reporting.
Is P2BAD something I can fix myself?
Topping up with fresh AdBlue is worth trying. On a Citroen, Peugeot, Ford, Mercedes or any other make, finding the actual cause takes live NOx and dosing data. Related code P20EE often appears with it.
Can I have the AdBlue system deleted to stop P2BAD?
That's only possible on a vehicle kept off-road or heading for export. See our guide on whether an AdBlue delete is legal for the reasons.
Get P2BAD looked at where the vehicle is parked
Send us the registration and the countdown figure, and we'll come to the vehicle and find out what's pushing NOx too high.
More fault codes explained
Eccles, Manchester M30 0SF