OBD-II code · Powertrain (generic, extended)
P21CE Reductant Quality Module Performance
DEF quality module reports an internal performance fault — self-test failed or measurement loop unable to converge. The module may need replacement.
Is it safe to drive with P21CE?
Usually safe for short trips, but don’t ignore it: the underlying fault can get more expensive over time.
Common causes
- Most likelyInternal module fault
- Less likelyModule software outdated, reflash may resolve
- Less likelySupply voltage outside specification
Symptoms
- Check engine light or NOx warning on
- AdBlue/DEF level or quality warning
- Possible no-start countdown after ignore period
- Failed emissions inspection (NOx)
Repair at a glance
- Difficulty
- Hard
- DIY friendly
- Best left to a mechanic
- Typical labour
- 1–4 h
- Emissions test
- Likely to fail
- Parts involved
- Reductant Quality Sensor
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.