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sophia_tiger7

Mercedes ML Engine Power Loss and Error Codes Resolved

My 2003 Mercedes ML with a gasoline engine is giving me grief. It's got about 213000 km on it. Engine power is way down, like driving through molasses, and the computer keeps throwing error codes. I'm thinking it might be the ECU. I tried a system reset but it didn't change anything. Any ideas before I'm forced to sell?

Summary of the thread

A 2003 Mercedes ML was experiencing significant engine power loss and persistent error codes, leading to concerns about a faulty ECU. After considering potential causes, it was suggested to check the main relay, a common source of such issues. Upon inspection at a workshop, the main relay was indeed identified as the problem, causing the ECU errors. Replacing the relay resolved the power loss and error codes, restoring the vehicle's performance.

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4 comment(s)

johannacrystal3

Sounds rough! I had something similar happen on my old BMW, turned out to be a faulty sensor messing with the vehicle electronics. Have you checked the main relay? Sometimes a bad relay can cause ECU problems and give those symptoms. It's an easy and cheap thing to check before you get into ECU repair.

sophia_tiger7 (community.author)

Main relay, huh? Where would I even find that, and is there a simple way to test it? I’m not super familiar with automotive electronics, so ELI5 if you can!

johannacrystal3

The main relay is usually in the fuse box, either under the hood or inside the cabin. The owner's manual should have a diagram. Testing it involves checking for voltage and continuity, but honestly, if you aren't comfortable with that, best to take it to a workshop. Sounds like the reduced power and stored error are pointing at the ECU and I'd get that checked out.

sophia_tiger7 (community.author)

Okay, thanks so much for the advice! I took it to a shop. Turns out it WAS the main relay causing the ECU problems! They replaced it, cleared the error codes, and now it runs like new. Total cost 120€ for the ECU repair. I'm so relieved it wasn't anything major!

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MERCEDES

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ML