Emissions

P2204 — NOx Sensor Circuit Low Input (Bank 2 Sensor 1)

Severity: medium Drive with care, to a shop

What P2204 means

The engine control unit monitors the nitrogen oxide (NOx) sensor on bank 2, located upstream of the SCR catalyst. P2204 is set when the signal or voltage in that circuit falls below the expected range. The sensor data is used to calculate AdBlue (urea) dosing, so a fault can make the SCR system inaccurate or shut it down.

Symptoms

  • Check engine light on
  • SCR or AdBlue warning on the dash
  • Other SCR-related codes stored
  • Start countdown on some vehicles
  • Possible torque or power limitation

Possible causes

  1. Failed bank 2 NOx sensor or its control module
  2. Wiring short to ground
  3. Poor connection or corroded connector
  4. Damaged harness near the exhaust
  5. Exhaust leak near the sensor affecting readings
  6. Rarely, an ECU software issue

How to diagnose

  1. Scan all codes and freeze-frame data, noting other SCR or NOx codes
  2. Read live NOx sensor values and dosing system status
  3. Check AdBlue level and quality
  4. Inspect the sensor wiring and connector for chafing, heat damage, moisture and corrosion
  5. Test power, ground and signal circuits against the factory wiring diagram
  6. Check the exhaust for leaks upstream of and near the sensor
  7. Inspect the dosing valve, lines and SCR heater operation
  8. Look for technical service bulletins and software updates

Common fixes

  • Replace the bank 2 NOx sensor
  • Repair the short, wiring or connector
  • Fix the exhaust leak
  • Update ECU software if a bulletin calls for it
  • Clear codes and verify with a test drive after repair

Questions and answers

What does P2204 mean?

It means the bank 2 upstream NOx sensor circuit is reporting a low signal. The sensor itself or its wiring is the most common cause.

Can I drive with P2204?

For a short time, yes, but some vehicles count down starts or reduce power when the SCR system is faulty. Don't put off diagnosis.

How much does it cost to fix P2204?

It depends on the cause: a connector repair is cheaper than replacing a NOx sensor. Check wiring and exhaust leaks first before buying parts.

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.