P202C: Reductant Tank Heater Control Circuit High
Standardized SAE J2012 code · P20xx — Fuel & air metering and auxiliary emission controls
What does P202C mean?
The DEF tank heater control line reads above the expected voltage — short to B+ or open ground. The tank heater thaws the urea solution around the pump intake and keeps it liquid, since DEF freezes at about −11 °C. With the heating out of action, dosing is delayed or blocked in frost and the SCR catalyst cannot reduce NOx until the fluid has thawed.
The code tells you which monitor failed, not which part is broken. Test before replacing parts.
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)
Common causes
- High Short to B+
- Low Connector pins corroded - high contact resistance
- Low Supply wire pinched against B+ source
Likelihood is a general estimate across vehicles; your make and model may differ.
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