Emissions

P2202 — NOx Sensor Circuit Low Input (Bank 1 Sensor 1)

Severity: medium Drive with care, to a shop

What P2202 means

The engine control module detected that the signal or voltage in the bank 1 upstream NOx sensor circuit is lower than expected. This sensor sits ahead of the SCR catalyst and measures how much nitrogen oxide leaves the engine. The ECM uses it, along with the downstream sensor, to set the reductant (DEF/AdBlue) dose and judge how well the system works.

Symptoms

  • Check engine light on
  • SCR or DEF/AdBlue warning on the dash
  • SCR system inactive or dosing incorrectly
  • Reduced torque or power derate
  • Start countdown or restart lockout on some vehicles
  • Higher NOx emissions

Possible causes

  1. Failed NOx sensor (most common)
  2. Short in the sensor wiring harness
  3. Signal wire shorted to ground
  4. Connector damaged by exhaust heat
  5. Corrosion or water in the connector
  6. Fault in the sensor's internal control unit
  7. Rarely, ECM fault or outdated software

How to diagnose

  1. Scan for all codes and freeze frame data, noting other SCR or NOx codes
  2. Read live NOx sensor values at operating temperature and compare to expected readings
  3. Check DEF level and quality and the dosing system status
  4. Inspect the sensor, connector and harness for heat damage, chafing, corrosion and moisture
  5. Test sensor power, ground and signal circuits against the manufacturer wiring diagram
  6. Check the harness for shorts to ground and open circuits
  7. Check the dosing valve, lines and heater if related codes are present
  8. Look for technical service bulletins and software updates for the vehicle

Common fixes

  • Replace the NOx sensor
  • Repair or replace the damaged wiring harness
  • Replace or clean the connector and add heat protection
  • Update ECM software per the manufacturer bulletin
  • Clear the code and complete the SCR system relearn or verification after repair

Questions and answers

What does P2202 mean?

It indicates a low signal in the upstream NOx sensor circuit (bank 1) on a diesel with SCR. The sensor itself, or its wiring and connector, is the most common cause.

Can I drive with P2202?

For a short time, yes, but power may be reduced and some vehicles will eventually restrict or block starting. Get it diagnosed soon.

Should I replace the NOx sensor right away?

Not before checking the harness, connector, power and ground. The sensor is expensive, and replacing it without testing the wiring may not fix the problem.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.