MARCH 2024 AFTERMARKET 31 After some research, we were unable to program a new unit with our diagnostic equipment and the customer was contacted and advised of costs involved and if they wanted to fix the vehicle it would need to be recovered to the local Mercedes dealer. Having sentimental value, the customer decided he wanted the car to be repaired so the vehicle was taken away to be repaired and I thought that was the end of the job however a few weeks later it was booked back in. It now started and ran, but had a list of new symptoms the customer said were not present before the vehicle developed its previous no crank and flashing key symbol issues. Investigating Reading the job card, the vehicle now had an ABS warning light illuminated, the radio did not work, both electric windows did not operate at all and the heater blower motor was inoperative. The local Mercedes dealer had advised a new ABS module was required at a cost amounting to four figures, and further investigation was required to look into the rest of the faults. However, the customer wanted a second opinion so paid for the work carried out and removed it from the dealership. I decided to pick the ABS fault first and work from there. Connecting and reading faults, we had one code stored. Please refer to Fig.2. This referred to a fault at the ABS valve relay. Checking technical data listed the possible cause as internal module error and suggested checking module power and ground supplies. It looked like the Mercedes dealer was possibly correct then but you never condemn a part without carrying out all possible tests first so I gained access to the ABS module and checked the wiring referring to a diagram. Upon testing the power supplies, I found no 12v power supply at pin 6 and checking against the diagram showed it to be supplied by the front SAM, but this was new? I then decided to have a quick study of the wiring diagrams for the windows and other non-working items for a possible link and interestingly It was noted that all items were fed from the front SAM with some sharing the same connector. Technical information With my newly found information, the next step had to be to gain access to the front SAM and the relevant connectors and test from there. Upon removing the unit from its housing and lowering it to gain access to the wiring connectors, I was met with what you can see in Fig.3. Not only one connector not fitted but two different connectors left unplugged from the new SAM unit. Reconnecting both and retesting the customer complaints showed all issues to now be fixed. The customer was delighted and were glad they got a second opinion as following the Mercedes dealership diagnosis would not have fixed this car! Now I am not one to badmouth dealerships and their technicians, but something went wrong here and mistakes were made which could have cost the customer thousands of pounds. I know I sound like a stuck record with my articles, but I cannot emphasise enough the importance of having a solid test plan, process and technical information to help fix cars coming through your workshop. I had never worked on this model of car before but armed with the information I needed along with a good understanding of system operation I was able to make a diagnosis and repair, and get the car back to the customer to use as intended. Fig. 2 www.aftermarketonline.net Fig. 3 Fig. 1
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