P2205: NOx Sensor Heater Control Circuit/Open Bank 1 Sensor 1
What to do
The car drives normally and the inducement countdown described under P2200 still applies. Worth knowing for the future: these sensors are hardest hit by short journeys, because the exhaust never dries out and the heater has to work around condensation on every start. Where the vehicle's use allows it, a longer run occasionally is genuinely kinder to the emissions system than a series of short ones — the same is true of the particulate filter.
What this code means
A fault in the circuit driving the NOx sensor's heater. The heater is not an accessory on this sensor — without it there is no measurement at all, so a heater fault and a sensor fault have the same practical result.
Why the element has to be hot. The measurement depends on oxygen ions moving through a ceramic electrolyte, and that ceramic only conducts them at high temperature — several hundred degrees, well above what exhaust gas alone reliably provides at low load or in traffic. So the sensor carries a heater whose job is to hold the element at its working temperature regardless of what the exhaust is doing. Cold, the sensor is not inaccurate; it is blind.
And why the heater is deliberately delayed after a cold start — which explains a real ownership pattern. A cold exhaust is full of condensation. Combustion produces water, and until the pipe is warm that water sits in it as liquid. A droplet reaching a ceramic element already heated to working temperature causes it to crack from thermal shock, instantly and permanently. So the module holds the heater off, or ramps it very gently, until it calculates the exhaust is dry.
The consequence is that short journeys are unusually hard on these sensors. A vehicle that never runs long enough to dry its exhaust spends its life in the condensation phase, accumulating water in the system and giving the heater strategy a difficult problem on every start. It is one of the more concrete reasons why the same sensor lasts markedly longer on one car than another, and it is worth knowing rather than treating the failure as bad luck.
A heater circuit fault, then, disables the sensor and starts the inducement sequence described at P2200 — with the car driving perfectly throughout.
Likely causes
Start here
- Faulty NOx sensor · moderate
- Open circuit in heater wiring · moderate
- Corroded or loose connector · easy
Less common
- Blown fuse or failed supply · easy
- Faulty NOx sensor control module · specialist
- Thermal shock damage from exhaust condensation · moderate
Symptoms
Components involved
Information, not instruction
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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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