I was recently tasked with looking at a vehicle which had the dreaded 500-miles-or-less-until-the-vehicle-cannot-be-started warning on the dash display. We have all been there before with this sort of issue. This is a typical warning you will see on vehicles fitted with an AdBlue emission system if there is a fault present. The vehicle in question was a Range Rover Evoque 2016 2.0TDI.
    
The customer who brought the vehicle to me was a trade customer. They advised that the vehicle originally came into them for repair for an engine warning light which intermittently illuminated. The fault code was for Nitrogen Oxide (NOX) sensor 2 no signal. I started by carrying out a full system scan of the vehicle as I would routinely do. The result was multiple fault codes stored in the engine management system control module relating to the AdBlue system. Due to having so many codes stored, I checked all the relevant freeze frame data for each code and then erased them. Following this, I attempted to carry out a road test, but a fault code returned almost immediately for no communication present with NOX Sensor B.

Signal and communication
Armed with this information, I thought it would be a fairly straightforward diagnosis. However, I was wrong. It never 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.