rudolfsilver4
Mercedes GLS Diesel Engine Control Unit Problem
Summary of the thread
A 2022 Mercedes GLS diesel was experiencing poor engine performance and an error code indicating a defective engine control unit (ECU). The issue was suspected to be related to vehicle electronics or the control system. A suggestion was made to check the main relay, which could be a simple and inexpensive fix. After replacing the main relay, the engine performance improved, and the error code disappeared, resolving the problem without needing a dealership visit.
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4 comment(s)
rudolfsilver4 (community.author)
Thanks for the tip! Where exactly is the main relay located? Is there a way to test it, or should I just replace it outright? The error is pretty consistent now, it comes on almost immediately after starting the engine.
kevinknight93
Location varies, check your owner's manual for the exact location of the main relay. Testing requires a multimeter and some electrical knowledge, so unless you're comfortable with vehicle electronics, I'd suggest just swapping it. If that doesn't fix it, you're probably looking at deeper ECU problems and a workshop visit. They charged me about 120€ in the end.
rudolfsilver4 (community.author)
You were spot on! Replaced the main relay, and the engine is purring again. The error code is gone, and full power is back. Massive thanks for saving me a ton of money and a trip to the dealership!
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MERCEDES
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GLS
kevinknight93
Sounds familiar. I've got a GLS too, and had similar engine performance issues. Error memory also pointed to the computer module. Check your main relay, it could be a cheap fix before you dive into replacing the whole ECU. Is the error consistent, or does it come and go?