P202B: Reductant Tank Heater Control Circuit Low

P202B belongs to the electric heater in the DEF tank and reports a low reading in its control circuit. Generically that means a signal sitting too low, for example a grounded wire or a drive output pulled down. Volkswagen gives a concrete test on the 2014 Touareg 3.0 TDI: right at the start of heating the element's conductance must reach a minimum, and a value under 0.30 S, i.e. more than about 3.3 Ω, sets P202B. The element still conducts, unlike the open-circuit case P202A, but draws too little current to thaw the tank in time. Corroded pins, a partly damaged element or a wire chafed against the body are typical. The heater is needed only in frost, so the code often surfaces in the first cold weeks; while temperatures are mild, DEF dosing usually continues.

Medium severity. Can I keep driving?Deal with it soon. If the instrument cluster shows a countdown, the car may not restart once it reaches zero.

Symptoms

Malfunction indicator lamp on
DEF stays frozen longer after cold starts

Most likely causes

Corroded heater connector pins adding resistance
Heater element partly damaged, resistance too high
Control wire chafed through to ground

What to check, in order

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

Check the AdBlue/DEF level and quality, and do not add additives or water
With the connector unplugged, check whether the signal wire is making contact with ground.
Look for white crystals around the injector and the tank
Check connectors and heaters with the scanner
Run the dosing test available on your diagnostic tool
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 P202B means

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

Frequently asked questions

Can I keep driving with code P202B?

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

What causes code P202B?

The most common causes are: corroded heater connector pins adding resistance; heater element partly damaged, resistance too high; control wire chafed through to ground.

Related codes

Sources

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.