Cause
Faulty NOx sensor control module
The small electronics package that comes as part of a NOx sensor, failed. These are not simple sensors: the element needs around 800°C and a two-stage measurement, so each sensor carries its own module which runs the heater, performs the measurement, and reports the result over the vehicle's data network rather than as a voltage.
That architecture is why a communication fault presents as a sensor fault. If the module cannot talk, the engine module reports the sensor as faulty — while the sensing element is perfect. So a network or bus code stored alongside is worth reading before a part is ordered.
It is almost never sold separately. The module is moulded into the harness a fixed distance from the sensor, so a module fault means buying the whole assembly — which is why eliminating the connector, the supply and the earth first genuinely matters here.
Its position is what kills it. It hangs under the vehicle in road spray and salt, close enough to the exhaust to be heat-cycled continuously. Water ingress and heat-fatigued solder joints are the ordinary findings.
Where two of these sensors are fitted, they are usually not interchangeable — different lengths, different network addresses — so confirm the part before fitting, and expect some vehicles to require coding afterwards.
Typically a moderate job.
Codes this can cause (7)
Codes where this is a likely explanation first, rather than merely a possible one.
- P229E NOx Sensor Circuit Bank 1 Sensor 2 Likely for this code Moderate
- P2200 NOx Sensor Circuit Bank 1 Sensor 1 High
- P2205 NOx Sensor Heater Control Circuit/Open Bank 1 Sensor 1 High
- P2208 NOx Sensor Heater Sense Circuit Bank 1 Sensor 1 Moderate
- P225C NOx Sensor Performance - Signal Biased/Stuck High Bank 1 Sensor 1 Moderate
- P225D NOx Sensor Performance - Signal Biased/Stuck Low Bank 1 Sensor 1 High
- P22A7 NOx Sensor Heater Sense Circuit Range/Performance Bank 1 Sensor 2 Moderate
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.
Others who found this
Be the first to write this up
Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
Sign in or create an account to add what you found about Faulty NOx sensor control module.