NOx Sensor Circuit Range/Performance (Bank 1)

Possible causes

• CommonFailed NOx sensor
• CommonCorroded connector - these live in the hottest, dirtiest part of the vehicle
• CommonWiring damaged by exhaust heat or road debris
• CommonSensor contaminated by soot, oil or coolant in the exhaust
• PossibleSensor seized in the exhaust and damaged during a previous removal
• PossibleReductant system fault upstream, so the sensor correctly reports poor conversion

What you might notice

• Check engine light on
• Reduced power or limp mode
• Emissions system warning
• Restart countdown on some vehicles
• Failed emissions test
• Often no symptom the driver notices at first

What to check, in order

1. Read all codes first. A reductant system fault alongside this one usually means the sensor is reporting the truth, and the SCR system is the real problem.
2. Inspect the connector for corrosion and heat damage. These connectors take the worst environment on the vehicle and fail more often than the sensing element does.
3. Check the wiring where it runs along the exhaust and under the vehicle.
4. Expect the sensor to be seized in the exhaust boss. Penetrating oil and patience beat force - a snapped sensor turns a large job into a much larger one.
5. Establish the price before committing. NOx sensors are among the most expensive sensors on a modern diesel, and on many vehicles the sensing element and its module are supplied as one assembly.