P209F: Reductant Tank Heater Control Circuit Performance
What to do
Mention the weather and the length of your journeys. Heating a tank of frozen reductant takes a long time, and a vehicle doing short trips in a hard frost may genuinely never get there — which is the system working rather than failing.
Get it looked at before deep winter regardless. If the heater genuinely is not working, the first sustained frost leaves the emissions system unable to dose, and that starts a countdown towards the vehicle refusing to restart.
Ask whether the reductant temperature sensor has been checked, since the module works this fault out from temperature and a faulty sensor produces it with a good heater.
If the car is slow to warm up generally, mention that too — on vehicles that heat the tank with engine coolant, a thermostat stuck open causes this directly.
What this code means
The reductant tank heater is being commanded but the tank is not warming as expected.
Performance separates this from the circuit codes beside it, and the distinction points the diagnosis somewhere quite different. The wiring is intact and the heater is being commanded — the module is judging the result, and the result is not appearing.
Which means the module is inferring this from temperature, and that creates the first thing to eliminate: a faulty reductant temperature sensor produces this code with a perfectly good heater. The heater may be working and the thermometer lying.
Where the temperature reading is trustworthy, the causes divide by heating method.
- On coolant-heated systems, a diverter valve stuck closed, an airlock in the heating circuit, or an engine that never gets warm enough to supply heat in the first place. A thermostat stuck open shows up here in winter.
- On electrically heated systems, an element that has partly failed — still drawing some current, no longer producing the heat it should.
There is a legitimate non-fault worth knowing about. Heating a full tank of fluid from well below zero takes a long time, and a vehicle used for short journeys in a hard frost may genuinely never reach target. The system is working; the journey is too short.
The consequence is seasonal. Nothing happens in summer, and the first sustained cold snap produces frozen fluid and an inducement countdown.
Likely causes
Start here
- Faulty reductant tank heater · moderate
- Faulty reductant temperature sensor · moderate
Less common
- Thermostat stuck open · moderate
- Air trapped in the coolant circuit · moderate
- High resistance in sensor wiring · moderate
Symptoms
Components involved
Information, not instruction
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Community experience
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