JUNE 2023 AFTERMARKET 29 goes the way you would like it to, especially at the end of the day. I put the vehicle on the ramp and obtained a wiring diagram to check the wiring directly at the NOX sensor. Upon first inspection, it was clear the sensor had already been replaced. I contacted the customer, and they confirmed the sensor was indeed both new and genuine from the manufacturer. I then checked the wiring to the sensor. These types of sensors are fairly straightforward to check because they have only four wires which have signals on. These are power, ground and CAN bus communication. I firstly checked the power and ground and confirmed these matched the genuine wiring schematic. Please refer to Fig.1. Next, I then connected an oscilloscope to the circuit to monitor the CAN bus signal. I found the CAN bus was shorted to each other and what would appear to be 12v. Please refer to Fig.2. The simplest next test was to unplug the sensor and to monitor the CAN bus signal. I found with the sensor unplugged the short was no longer present and the CAN bus signal returned, which would mean that the sensor was faulty wouldn’t it? Please refer to Fig.3. Slightly concerned I was missing something as the sensor had already been replaced, I decided to contact Neil Currie. As well as being the winner of Top Technician 2019, he is a contributor to this very magazine and a Land Rover/Range Rover guru to boot. He advised me that if the sensor has been replaced and it is a genuine sensor provided by Range Rover, then the pin configuration has been changed and you are required to move the pins around in the connecting plug in order for the new sensor to operate. This has been done due to a change in manufacturer used by Range Rover to produce this style sensor because of a lack of available original manufacturer NOX sensors. The details can be found here from a bulletin released by JLR. Full system scan After de-pinning the connector and swapping around pin 2 (CAN) and pin 4 (Ground), I rechecked the CAN bus signal and found the signal is now correct and is no longer shorted. Please refer to Fig.4. After carrying out a full system scan, clearing and resetting the AdBlue counter, I now found that the warning for 500-miles-remaining had, vanished and there were no fault codes returning. This vehicle was now fixed. I thought this was a very interesting case study as both the aftermarket and genuine diagrams both show the original wiring of the NOX sensor and there is no reference to a modification, unless you are aware of this issue or have access to Range Rover’s technical service bulletins this would certainly take you up the diagnostic garden path. Luckily for me, networking with the finest technicians in the country is a great way to stay up to date with these types of modifications. www.aftermarketonline.net Networking with the finest technicians in the country is a great way to stay up to date with these types of modifications ” Fig. 1 Fig. 3 Fig.4 Fig. 2
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