SCR NOx Catalyst Efficiency Below Threshold (Bank 1)
Most modern diesels inject AdBlue into the exhaust. In the SCR catalyst, AdBlue turns nitrogen oxides (NOx) into nitrogen and water. Two NOx sensors check that it works.
What the car has detected
The NOx sensor after the catalyst reads almost as much NOx as the one before it: the system is not removing them.
The car keeps running, but many warn that it will not start after a number of kilometres if it is not fixed. Have it checked soon and do not ignore the countdown on the dashboard.
Symptoms
- Engine warning light on
- AdBlue warning or a countdown of kilometres until no start
- Limp mode in some cases
Possible causes
- Poor-quality, diluted or crystallised AdBlue
- Blocked or faulty AdBlue injector
- Faulty NOx sensor
- Exhaust leak ahead of the catalyst
Checks for the garage
- First check any other NOx sensor codes
- Check the AdBlue quality and dosing
- Look for exhaust leaks ahead of the catalyst
Next step
Ask for the AdBlue quality, the AdBlue injector and the NOx sensors to be checked before the catalyst is replaced.
Go to a garage soon. Always use AdBlue from a sealed container that meets ISO 22241.