P202C: Reductant Tank Heater Control Circuit High

P202C is the high-side fault of the DEF tank heater circuit: the module sees a value above the allowed range, as when the wire touches battery positive or an element that conducts far too well. On the Touareg 3.0 TDI of model year 2014, Volkswagen flags it when the element's conductance at the start of heating exceeds 0.62 S, below roughly 1.6 Ω, which hints at an internal short. On 2025 Ram 2500 to 5500 with the 6.7 L Cummins, Chrysler's bulletin 08-076-26 lists P202C next to other DEF heater and pressure codes and cure them with new software for the DEF control unit; there the fault came from calibration, not from hardware. With a real short the fuse may blow or the driver protect itself, so the tank stays unheated. In winter the system may then warn and count down to a speed limit.

Symptoms

• Malfunction indicator lamp on
• Service DEF message, later speed limited
• Heater fuse may blow

Most likely causes

• DEF control unit calibration (software update on some models)
• Heater element with internal short, resistance too low
• Heater control wire shorted to battery voltage

What to check, in order

Start with the simplest. You can tick off each step.

1. Check the AdBlue/DEF level and quality, and do not add additives or water
2. Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
3. Look for white crystals around the injector and the tank
4. Check connectors and heaters with the scanner
5. Run the dosing test available on your diagnostic tool
6. Replace parts only when the test points to that component

Good to know

• Repair difficulty: medium
• It can trigger limp mode.
• It affects emissions.

What each character of P202C means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 0: Subsystem depends on the code range
• 2C: Specific fault in that system

Frequently asked questions

Can I keep driving with code P202C?

Deal with it soon. If the instrument cluster shows a countdown, the car may not restart once it reaches zero.

What causes code P202C?

The most common causes are: dEF control unit calibration (software update on some models); heater element with internal short, resistance too low; heater control wire shorted to battery voltage.

Related codes

• P202AReductant Tank Heater Control Circuit/Open
• P202BReductant Tank Heater Control Circuit Low
• P209FReductant Tank Heater Control Circuit Performance
• P20BCReductant Heater A Control Circuit High

Sources

• static.nhtsa.gov: MC 10074008 2280
• static.nhtsa.gov: MC 11029671 0001
• en.wikipedia.org: Diesel exhaust fluid

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.