OBD-II code · Powertrain (generic, extended)
P20AF Reductant Metering Unit Temperature Sensor Circuit High
Metering unit temperature sensor above upper plausibility — open signal or short to B+. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.
Is it safe to drive with P20AF?
Usually safe for short trips, but don’t ignore it: the underlying fault can get more expensive over time.
Common causes
- Most likelyOpen signal line
- Less likelyConnector pins corroded - high contact resistance
- Less likelySupply wire pinched against B+ source
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 Metering Unit
Related codes
- P20ACReductant Metering Unit Temperature Sensor Circuit
- P20ADReductant Metering Unit Temperature Sensor Circuit Range/Performance
- P20AEReductant Metering Unit Temperature Sensor Circuit Low
- P20B0Reductant Metering Unit Temperature Sensor Circuit Intermittent/Erratic
- P20B1Reductant Heater Coolant Control Valve Circuit/Open
- P20B2Reductant Heater Coolant Control Valve Performance/Stuck Open
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.