P22A7: NOx Sensor Heater Sense Circuit Range/Performance Bank 1 Sensor 2
What to do
Ask for the connector to be inspected for heat damage as well as corrosion. This circuit carries real current, so a failing connection burns rather than just corroding, and the discolouration is usually visible.
Mention what kind of journeys the car does. Very short trips never dry the exhaust out, and these sensors are damaged by water striking a hot element — which is why short-journey vehicles get through them. An occasional longer run genuinely helps.
Ask whether other faults from the same sensor are stored. The heater is what makes the sensor work at all, so a heater fault usually explains them and one repair clears several.
The car will drive normally, so time the repair around your MOT.
What this code means
The heater feedback circuit on the downstream NOx sensor is not behaving credibly.
A NOx sensor's heater is not an accessory — it is what makes the sensor exist, and the way it is controlled explains this code and, more usefully, explains how these sensors die.
The element must reach around 800°C, so the heater is powerful and its temperature is controlled closely by measuring the element's own resistance. This code says that feedback measurement is wrong.
And here is the part worth knowing, because it is the leading cause of NOx sensor failure and it is preventable. Exhaust gas contains water vapour, which condenses in a cold exhaust. A ceramic element heated to 800°C that is struck by a droplet of water cracks instantly — thermal shock. So the module deliberately delays heating until it calculates the exhaust has dried out, which can be several minutes.
A heater control fault can therefore destroy the sensor rather than merely disable it, by heating too early. And a vehicle used only for very short journeys never dries its exhaust properly, which is why short-journey cars eat these sensors.
Check the connector for corrosion and heat damage first. This circuit carries real current, so a marginal terminal heats and burns rather than merely corroding — look for discoloured plastic rather than only testing continuity.
Likely causes
Start here
- Faulty NOx sensor · moderate
- High resistance in sensor wiring · moderate
- Corroded or loose connector · easy
Less common
- Thermal shock damage from exhaust condensation · moderate
- Faulty NOx sensor control module · moderate
Symptoms
Components involved
Information, not instruction
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Community experience
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