OBD-II code · Powertrain (generic, extended)
P202C Reductant Tank Heater Control Circuit High
The DEF tank heater control line reads above the expected voltage — short to B+ or open ground. The sensor heater warms the element to operating temperature (~600 °C); without it the lambda sensor stays inactive in closed loop and the ECM cannot trim mixture.
Is it safe to drive with P202C?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyShort to B+
- 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
- Medium
- DIY friendly
- Best left to a mechanic
- Typical labour
- 0.7–2.5 h
- Emissions test
- Likely to fail
- Parts involved
- Reductant Tank Heater
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.