NOx sensor checks in Stuttgart: test before replacing

How is a NOx fault assessed?

First, we establish the fault status, operating data and affected sensor's position. Power supply, heating, communication and the live reading are then checked for plausibility against operating conditions.

The sensor measures within a chain of systems. Possible exhaust leaks, SCR dosing and—where available—the relationship between readings before and after the catalyst are therefore considered.

• Establish sensor position and fault status
• Check power supply, heating and communication
• Check the live reading against the operating state
• Include the exhaust path and related SCR systems

Why a NOx code can have several causes

A NOx sensor measures exhaust values within a complex system. Incorrect dosing, an ineffective catalyst or a leak can produce abnormal readings even when the sensor itself is not the only cause.

Software versions and manufacturer-specific strategies can also affect when a fault is logged.

Sensor fault or system response?

A sensor-circuit fault, an implausible signal and a measured high nitrogen-oxide concentration point diagnostics in different directions. The exact code description and status therefore matter more than a brief internet summary.

After sensor replacement, vehicle-specific initialisation, adaptation or another plausibility test drive may also be needed. We check whether this applies to the particular vehicle.