P2201: NOx Sensor Circuit Range/Performance Bank 1 Sensor 1
What to do
Do not let this be treated as a failed sensor until the system it watches has been checked. This code fires when NOx output is too high, and a sensor accurately reporting a genuine problem looks identical to one that has drifted. Have the reductant level and quality, the dosing system and the EGR checked first — an empty or wrongly filled tank, crystallised deposits or a stuck EGR valve all produce this, and all of them will produce it again with a new sensor fitted. The inducement countdown described under P2200 applies, so this does need dealing with rather than deferring.
What this code means
The NOx sensor is working and reporting a figure the module does not accept. Before anything else: this code very often means the sensor is right.
That distinction is the whole of this page. A range/performance code says a reading is implausible — but "implausible" is judged against what the module expects when the aftertreatment is functioning. A sensor accurately reporting that far too much NOx is leaving the vehicle produces exactly the same code as a sensor that has drifted. One of those is a messenger and the other is the fault, and they are not distinguished by the code.
So the question to ask first is not whether the sensor is good, but whether there is anything for it to measure correctly. The reduction system it watches can fail in several ordinary ways, all of which make NOx output genuinely high:
- No reductant, or the wrong fluid. An empty tank, or something other than the correct urea solution put into it, and there is nothing to react with.
- Crystallised deposits blocking the injector or coating the catalyst, which is the characteristic failure of these systems and is covered at P2037 and P2047.
- A dosing fault — the injector not delivering, covered at P2047.
- A catalyst below working temperature, which is normal on short journeys and abnormal if it persists.
- An EGR fault, since recirculation is the other half of NOx control and a valve stuck closed raises combustion temperature and NOx output together.
Every one of those is a real fault that a new NOx sensor will report just as faithfully as the old one did. Fitting an expensive sensor because it delivered bad news is the characteristic error of this family, and it is expensive precisely because the part is.
The sensor genuinely can drift, and does — they age, and soot and sulphur contamination degrade them. But that conclusion belongs after the system has been checked, not before. Where a pair of sensors is fitted, comparing them across a range of conditions is what separates a drifted sensor from a catalyst that is not converting.
Likely causes
Start here
- Reductant tank empty or incorrectly filled · easy
- Crystallised reductant deposits · moderate
- Faulty NOx sensor · moderate
- Faulty reductant injector · moderate
Less common
- Stuck EGR valve · moderate
- Degraded reduction catalyst · specialist
- Exhaust leak near the sensor · 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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