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Mystery Mercedes

Case study on a Mercedes Benz that had more than one electrical gremlin, what caused them and how the problems were solved
Thursday, August 20, 2015 - 07:00
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Limitations — we all have them. Every now and then we should see if the limitations we had in the past still exist today. After all, if we automotive repair professionals live by the constant improvement model then it’s likely we are now better tooled, equipped and trained to perform a task that was previously impossible. Unfortunately, not everyone lives by that model.  

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In trying to help someone recently, I tested one of my limitations. A shop owner asked me to look at a Mercedes-Benz SUV; however, I told him I didn’t possess the factory tool for the Mercedes and have inexperience with the brand (I have focused my career on Asian and Domestic vehicles).

He said others had spoken so highly of my skills and he’d prefer to have a mobile technician come to his shop than to tow it somewhere where he “didn’t know what might happen to it.”  Right now, it’s a mystery what’s wrong. I promised the shop owner I would put forth my best effort, charge by the hour and utilize all the tools at my disposal. But I still may not be able to finish the job.  I warned him payment would still be expected even under those circumstances.  He asked how soon I could look at it.

The story begins in a different shop, one that’s owned by a regular customer of mine, where I was programming a vehicle after a module installation.  “Chuck” (may not be his real name) called to ask advice from my regular customer about how a 2008 MB GL550 Active Suspension fault could be causing A/C problems.  My customer, an air conditioning specialist, agreed that if Chuck would bring the vehicle over, he’d look at it briefly at no charge. Within a few minutes a pickup truck appeared in the parking lot towing a trailer upon which was the almost completely assembled vehicle in question. When my customer heard what had transpired to the vehicle in tow he immediately (and intelligently) tossed it in another direction.  Follow along – this gets fun.

The vehicle was originally brought to Chuck’s shop with the complaint that the A/C blows warm. Chuck decided it needed a compressor because “when I applied 12 volts with my Power Probe to the A/C compressor connector, the clutch would not engage.”  After replacing the compressor he had the same problem, but now, before he could get the SUV’s engine to even crank, he spent hours determining he must first remove the air suspension compressor relay. Note — this phenomenon was not present prior to the A/C compressor replacement (and to this day I’ve not understood how he came to either conclusion). Now that the engine starts, there are numerous lights illuminated on the instrument cluster and many comfort and entertainment systems don’t work. In addition, if the air suspension relay is reinserted, the engine stops running. Are you wondering about Chuck’s limitations yet? What would be your first steps here (besides turning and running as fast as you could)? 

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