P20C2: Reductant Heater C Control Circuit Performance
What to do
Worth fixing before winter even though the car drives normally. This heater keeps the return line clear, and that line is how the system empties itself after you switch off so nothing is left to freeze and split overnight. With it faulty, a hard frost can damage parts that would otherwise have been fine.
Ask whether several heater faults are stored. If they are, one shared connection is usually the cause rather than several failed heaters — a much smaller repair.
Ask which part this heater serves on your vehicle, since the lettering varies between manufacturers.
Mention if you have stopped hearing a pump run for a minute or two after switching off, which is that purge working and a genuine clue if it has stopped.
What this code means
The third reductant heater circuit is being commanded but not performing as expected.
Heater C is commonly the return line, the hose carrying fluid back to the tank, though as with the rest of this set the lettering must be confirmed against the vehicle's own documentation.
The return line matters more than its name suggests, and this is the code where that is worth explaining. Most systems purge fluid back to the tank when the engine stops — pumping the lines empty so nothing is left to freeze and split them overnight. The return line is how that purge happens.
Which means a frozen or blocked return line defeats the freeze protection for the entire system. The purge cannot complete, fluid stays in the supply line and injector, and the next hard frost damages hardware that would otherwise have been protected.
So this code is worth attending to before winter even though nothing is visibly wrong. It is protective rather than functional, and its failure is only discovered when the protection was needed.
The causes are the family's: a partly failed element, a misreporting temperature sensor, a corroded connector, or on coolant-heated systems a diverter or airlock.
Where several heater codes are stored together, look at the shared supply and earth first. One bad connection starves the whole set, and that is a far smaller repair than several heated line assemblies.
Likely causes
Start here
- Faulty reductant line heater · moderate
- Corroded or loose connector · easy
- Faulty reductant temperature sensor · moderate
Less common
- Blocked reductant return line · moderate
- High resistance in sensor wiring · moderate
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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