May 2020

BY Neil Currie E very now and then, you get a job that is unique. Once fixed, you never seem to get anything like it again. I recently had this with a vehicle and thought I would show how an unlikely fix was achieved, and the thought process behind it. The vehicle was a Land Rover Discovery 3. As I have mentioned before, I work at a Land Rover specialist, so we see a lot. This one was recommended to us after another garage (which I seem to mention in most articles) had been unable to enact a repair. The customer’s complaint was that the battery had gone flat overnight after the interior lights had been left on. A friend had then jump- started the vehicle with jump leads. However, they had connected the jump leads with the wrong polarity onto the battery, and now the poorly Discovery wouldn’t start. It also had a dashboard lit up like a Christmas tree. Method Confirming the complaint, I sat in and cranked the vehicle and it spun over but did not fire into life. I then had a think about where to go next. From experience, when this happens fuses will normally blow to protect circuits. If the customer is lucky, it’s just a case of replacing the fuse, recharging the battery and off they go. I could either run through all the fuses in each fuse box, or I could connect a scan tool and carry out a global fault check to see if I could gain some direction. Perhaps an ECU wasn’t communicating and it was fuse fed, which would allow me to narrow it down to a certain fuse rather than checking them all. With these types of faults in my opinion there is no wrong way to approach it as long as its methodical. Knowing this vehicle and its layout, I already knew that both fuse boxes, mainly the interior one, house a lot of fuses. As a result, I decided to go down the scan tool route to see if some diagnostic direction could be gained faster. Reading the engine control module showed a list of faults (fig.1; fig.2) but also indicated I had communication so the module was receiving power. The rest of the vehicle scan reported incorrect data from the engine ECU in most modules, which explained the other warning lights. When this model has information broadcast onto the can bus network which indicates there is faults within a module, it is normal to see multiple warning lights illuminate then clear when the faults have been rectified. Another observation I made was when the engine cranked, if the anti-theft system had been affected the vehicle would not crank whatsoever so hearing the starter turn also indicated that the security system was happy. Knowledge versus information This is where system knowledge is beneficial, but will not apply to all manufacturers, so technical information may be required to find this out. I then focused on the engine control module faults and why the engine would not start. Checking Topix (Land Rover’s information website portal) for fault code setting criteria, most of the fault code info suggested testing the wiring at the ECU, and if ok to suspect a faulty Engine ECU. So, I printed off the wiring diagram and made a test plan. My plan was to check all powers and grounds at the control unit. Even though we could communicate and read fault codes and read live data, we still could be missing a power feed. Most control units have multiple power supplies both permanently and switched. The permanent feed is there mainly for what is known as KAM (keep alive 32 AFTERMARKET MAY 2020 TECHNICAL www.aftermarketonline.net CAN I FIX IT? YES, I CAN! Fig. 1 Neil shows how the proper use of process can help with fixing a kind of fault not regularly seen