davidschneider1
Mercedes GLS Diesel Preheating Issue
Summary of the thread
A 2017 Mercedes GLS diesel experienced issues with the preheating unit, indicated by a persistent engine preheat lamp, a check engine light, and exhaust smoke. Diagnostics suggested a defective preheating control unit or a fault in the cable or plug connection. The problem was resolved by replacing the preheating unit, which addressed all symptoms.
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4 comment(s)
davidschneider1 (community.author)
Regarding voltage consistency, what's the expected voltage range at the preheating unit connector for this Mercedes GLS model? Is there a recommended procedure for verifying this parameter, ensuring accurate assessment?
dominikblitz4
I don't have the exact specs for your car, but a multimeter should do the trick. If the voltage is erratic, it's likely the cable or plug you mentioned. It might be best to let a workshop handle it.
davidschneider1 (community.author)
Your assessment aligns with my initial suspicion of a defective part within the cable or plug connection. I engaged a certified workshop for diagnostics and component replacement. The preheating unit was replaced, resolving the preheating lamp issue, check engine light, and exhaust smoke. Thank you for your input.
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MERCEDES
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GLS
dominikblitz4
Sounds like a bad connection is plausible given the symptoms. Did you check the voltage at the preheating unit connector? Is it consistent with what the car electronics are expecting?