Fig. 1

CAN I FIX IT? Yes, I can!

Neil shows how the proper use of process can help with fixing a kind of fault not regularly seen

Fig. 2

Published:  05 August, 2020

By Neil Currie

Every 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.

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 memory). It can remember such things as the security link between the anti-theft system and other data, for example injector correction factors used for smooth running control and adaption memory for example the EGR valve. One reason a switched live is used is so that when the ignition is turned on, the module wakes up and is ready to work, and when the ignition is turned off can go to sleep and doesn’t drain the battery. There are other reasons for both which also can vary depending between petrol and diesel and manufacturers. Again, it’s important to have the correction information to hand to know the system operation.

With my information to hand I gained access to the ECU, which on this model is located behind the battery. Testing each power and ground under load proved all to be good, so according to Topix we now needed a new control unit as the incorrect polarity jump start has damaged the control unit. At this stage I was in agreement, and decided to phone my local dealer and price a new unit up. Brand new, this control unit was at the time around £800 plus VAT, then required fitting and programming. I then took a step back and had a think about if anything else could be done.

I remembered many years ago reading an article by James Dillon, where he advised always thinking of what tests you would do if the part/repair did not fix the vehicle and doing them beforehand. With this in my head I then thought what else could I do? What if it was just a software issue and a possible update would rewrite over what may just be corrupt data? I myself had never seen it before and did not know the answer but for the sake of updating the software with the Land Rover factory scan tool I decided to give it a go. If it didn’t work then I was happy it needed a new ECU and I had learned something in the process.

The module did have an update available so I ran the procedure and then when complete I cranked the engine to see what happened. To my surprise the engine fired into life and all of my fault codes cleared except the 2 x EGR faults which after further testing were both faulty (a common issue on this particular engine). The vehicle was rebuilt and given a road test and all was well confirming the complaint was fixed. The customer was then notified and advised of the EGR issue.

From this job, I learned that if there is possibly another test that can be carried out, do it and see if any more information can be gained. On this vehicle it was looking like a new ECU, so I had nothing to lose. It was just an idea I had, which I decided to do follow through on in the name of learning, due to my curiosity. Will this work every time? I highly doubt it, as in this case only the software was corrupted. If a large amount of current had made its way into the unit, then the small and fragile components would not have stood a chance which is what usually happens if they aren’t protected by a fuse. Luckily for the customer the repair only turned out to be a fraction of the cost of a new control unit and a lesson learned for his friend.

Related Articles


©DFA Aftermarket Media Ltd
Terms and Conditions