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Getting a first-time fix is a matter of keeping your head says Neil, no matter how complex the problem

Published:  20 January, 2022

In this article I am going to go over a recent job I had which initially looked to be much more complicated than it turned out to be. Fortunately, not jumping in with both feet, starting the diagnosis from the beginning regardless of what had been done before and planning my attack meant I got a first-time fix.
    
Second opinion
The car in question was a 2017 Ford Kuga. The customer’s complaint was that the speedometer didn’t work and the mileage and trip counters were blank (see Fig.1). The vehicle also had an ABS and traction control warning light illuminated and a hill descent fault. The customer then explained that they had received a letter through the post stating that their vehicle had a recall from Ford for a PCM update for oil dilution problems. As a result, the vehicle was booked into the local Ford dealer for this to be done. While the vehicle was there, the customer decided that the dealership could take a look at the aforementioned faults. The update was carried out along with a BCM update which was recommended for the faults. The customer was then phoned and told it was ready to be collected. However, upon pulling away from the dealership, the car had the exact same problems as it did when it arrived. The customer then returned to the dealership, and was told it was more than likely a faulty module causing the issues and would cost in excess of £1,000 to fix. It was at this point the customer decided to get a second opinion. The vehicle was then booked in with me to take a look and see if we could get to the bottom of the problem.

Confirming the complaint
As always, I started by confirming the complaint, and the faults matched what the customer had said (see Fig.2). I then connected a scan tool to do a global fault code read to see what faults were stored and take it from there. Once the scan had completed and saved, I was surprised to find I didn’t actually have many faults stored and the main code that kept popping up was C0031; Left front wheel speed sensor. I also had faults in other modules saying to either check the ABS system for faults, or invalid data had been received by the module, as is now commonplace on modern vehicles. Multiple modules use wheel speed data, not just the ABS system itself, so this is why they log faults for other modules. I didn’t have any modules failing to communicate so this indicated that it was more than unlikely a module was at fault. However, I still had the dashboard issue present which was a permanent fault and it could not be discounted.

Intrigue
What did intrigue me however was why the mileage and trip displays were just reading “----" and not numbers? What could cause this and why was it happening? Could it be a faulty instrument panel or perhaps a body control module issue? As in most cases now, it stores the main data for the vehicle including total mileage covered. I didn’t have any real fault codes to use as clues so I decided to focus on the ABS fault first, fix it, then go from there. It can be really easy with faults like this to go down a rabbit hole trying to find an issue that is not there. Experience has taught me to fix what you know is wrong first then reassess and then attack the faults which remain. We knew the ABS system had a fault so we fix it first then see what the dashboard displays.
    
My next step was to access live data and do some checks dynamically before I went any further. Displaying all four-wheel speeds showed a problem straight away. With the vehicle sitting stationary in the workshop, the left front wheel speed read 255km/h, which you wouldn’t expect. Meanwhile, the other three read 0, which you would expect as the vehicle wasn’t moving. Experience has taught me that on most Ford vehicles, not all though, 255km/h indicates a circuit problem, whether it be a sensor issue or wiring. I knew I had to do some tests to establish the cause of the fault.

Detached
I then removed the left front wheel to test the wiring and ABS sensor and a visual inspection found the cause of the ABS fault (see Fig.3). For some reason the wiring loom for the sensor had detached from the securing clip, which can also be seen in the picture, and had allowed the wiring to rub against the tyre and wear through to the point that it was now completely broken and became open circuit. I then cut back the insulation and repaired the wiring and checked live data before completing the repair. It is important to confirm the repair first before you fully assemble the vehicle only to find an issue still exists. Been there, done that and got the t-shirt. I now had all four sensors reading 0 km/h. Spinning the left front wheel while on the ramp showed the sensor to respond and read a wheel speed, so the wiring was then insulated correctly.
    
Knowing the ABS fault was repaired, the vehicle was then reassembled, but this time the wiring loom was secured away from the wheel and tyre. I then cleared all the fault codes in the vehicle and rechecked the customer’s complaint. I found that the car now had no faults stored in any module and the mileage and trip readings displayed correctly. A road test confirmed we also had a working speedometer and a final global fault code scan on return to the workshop showed no fault codes, so the vehicle was fixed.
    
What can be learned from this job? As I said earlier, it would have been very easy indeed to start chasing the mileage/trip display fault. This could possibly condemn the dashboard. Alternatively, I could have ended up removing it and sending it off for testing, only to then be told it had no faults and then be left wondering where to go next. Fix what you know is wrong first, then reassess the situation; Diagnostic work is much easier when you apply methodical thinking and work to a test plan specific to the vehicle and its faults, like I have mentioned in many articles before.




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