P2202: NOx Sensor Circuit Low (Bank 1)

What it means

The bank 1 NOx sensor circuit signal is below the expected range. This circuit code does not by itself identify the sensor failure mode or wiring fault.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test

How it works

The bank 1 NOx sensor circuit carries the sensor signal used to monitor exhaust nitrogen oxides. P2202 means the module sees the circuit signal below its expected range; it does not by itself prove that the sensor has failed.

Common causes

Most likely first.

1. Signal wire shorted to ground
2. Sensor failed low
3. Connector pins corroded - high contact resistance

Symptoms

• Check engine light or NOx warning on
• AdBlue/DEF level or quality warning
• Possible no-start countdown after ignore period
• Failed emissions inspection (NOx)

How to diagnose it

1. Read related codes and freeze-frame data to determine when the bank 1 signal went low and whether other sensor or supply faults appeared at the same time.
2. Inspect the bank 1 NOx sensor connector and harness for corrosion, chafing, heat damage, or a wire contacting ground.
3. Using the wiring diagram, test circuit continuity and check for a short to ground, poor terminal contact, and correct power and ground feeds.
4. If the wiring and feeds meet the manufacturer’s specification, test the bank 1 NOx sensor output and replace it only if the low signal follows the sensor.

Common fixes

• Repair a bank 1 NOx signal wire shorted to ground.
• Clean or repair corroded connector terminals and restore a sound connection.
• Repair a failed power or ground feed to the sensor assembly.
• Replace the bank 1 NOx sensor if circuit testing confirms it is producing a low signal.

Can I keep driving?

Cautious short-distance driving may be possible if there are no other symptoms, but NOx emissions control can be impaired and a DEF warning or countdown may appear. Follow any dashboard restart warning promptly.