Diesel exhaust fluid system (SCR)
P20EE
SCR NOx Catalyst Efficiency Below Threshold (Bank 1)
The system that uses diesel exhaust fluid (DEF) to clean the exhaust isn't reducing emissions enough.
Fix it soon
Can I keep driving? For a short while, gently. Have it checked in the next few days, and stop if the car feels, sounds or smells different. Many diesels count down to a speed limit or a no-restart if this isn't fixed. Don't ignore it.
What the words mean
- Bank 1 is the side of the engine with cylinder 1. A four-cylinder engine has only one bank.
Common causes
- Old, diluted or contaminated DEF
- A failed NOx sensor
- A clogged DEF injector or a failed pump
- A worn SCR catalyst
Listed roughly from most to least likely. The same code can have different causes on different cars.
What to do
- Check the DEF level and top up with fresh fluid from a sealed container.
- Watch the dash for a countdown message. Many diesels limit speed or refuse to restart after a set distance.
- Have the system diagnosed.
General guidance. Your owner's manual wins. If a red warning light is on or the car drives differently, stop safely and get help.
Track this automatically in Tagwell Auto
Tagwell Auto keeps your car's service dates and mileage, so when a code shows up you know what was done last. With a Bluetooth reader for the car's diagnostic port (called OBD-II), the phone app can read the code itself.