P202C: Reductant Tank Heater Control Circuit High
What to do
Get this fixed before winter rather than after. Reductant fluid freezes at around −11°C, and this heater is what stops that happening — so in warm weather you will notice nothing at all, and the first hard frost produces a car that starts counting down towards refusing to restart.
Ask for the connector under the vehicle to be inspected. These heaters sit near the tank where road salt and water reach them, and a corroded connector is the commonest cause.
Ask whether this vehicle heats the tank electrically or with engine coolant, since the repair is completely different and it is worth knowing what is being quoted for.
Do not top the tank up with anything other than the correct fluid while it is faulty — diluting it lowers its freezing point but ruins the emissions system.
What this code means
The reductant tank heater's control circuit is sitting higher than commanded.
Reductant fluid freezes at about −11°C, which is not an unusual temperature anywhere with a winter — so every vehicle that uses it carries heating for the tank and the lines. Without it, the emissions system simply cannot work in cold weather, because frozen fluid cannot be pumped or injected.
Heating is done one of two ways, and knowing which this vehicle uses decides the diagnosis. Some circulate engine coolant through the tank via a solenoid valve the module commands; others use an electric heating element. A control circuit code can therefore mean a coolant diverter valve or a heater element, and they are diagnosed nothing alike.
A control circuit reading high means a short to a supply voltage or an open circuit, and the module cannot tell which from inside. Measuring at the connector with the heater unplugged separates them in minutes.
The open-circuit case is the likelier here, because these heaters carry real current and their connectors live under the vehicle near the tank — road salt, water and stone damage all reach them.
The consequence is seasonal and easy to underestimate. In summer nothing happens at all. The first hard frost then produces a vehicle that cannot dose reductant, and the emissions inducement sequence starts counting down.
Likely causes
Start here
- Open circuit in control wiring · moderate
- Corroded or loose connector · easy
- Faulty reductant tank heater · moderate
Less common
- Water ingress into connector · easy
- Wiring shorted to voltage · moderate
Symptoms
Components involved
Information, not instruction
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