Two recent Autobiz helpline calls, regarding test information for Land Rover rear NOx sensors that had fault codes for poor NOx readings, SCR catalyst efficiency. The testing process for the SCR efficiency begins with serial data checks on the AdBlue system.

Important data groups included the reductant level and it is worth noting, the system will malfunction and not display a fluid level, if the tank is filled to the very top. Customers often overfill the system and this registers as empty. The level sensing system requires an airgap at the top of the reservoir, to accurately monitor the actual reductant level.

The next data PID is the system pressure. With the ignition and the engine not running, it will normally display 4 bar. When the engine is running, it should rise to 5 bar, with a maximum pressure of 8 bar.

Next, you will need to monitor the NOx sensor output from both sensors. This often requires the vehicle to be on a road test, to accurately monitor the part per million (PPM) figures. The exhaust needs to be up to full operating temperature. The two sensors should display a PPM value around 300-400 ppm upstream of the SCR catalytic convertor, and 10% of this figure on the downstream side (around 30 to 40 ppm). Readings in this range show good catalysation in the SCR Cat.

Testing the NOx sensor involves checking the power and ground supplies to the NOx module and CAN signal checks. But as these sensors are in short supply for most vehicle brands, and on back order for many months, problems have arisen with the replacement sensors supplied by Land Rover.

Recent calls to the Helpline showed that the signals from these are not as expected, when fitting the replacement parts. But with some research, we have found a Technical Service Bulletin (TSB) from JLR that the new sensors are wired differently from the original. The instructions can be seen by downloading the original story as a PDF.

Once the adaptations are completed for new parts replacement, a road test will need to be performed, this can take up to 40 minutes at cruise speeds, before the system returns to a proper operational mode.

To see or download this article click here.

There are lots more Tech Tips to view, and they are all searchable, on TechTips.ie.

To join the Autobiz Helpline, call 01-905-9500, and then press 2, for further information.