juliuswilliams1
E Klasse Diesel Engine Preheat Issue
Summary of the thread
The 2012 Mercedes E Klasse diesel had issues with the engine preheat lamp not turning off and the check engine light being on, accompanied by smoke during acceleration. The suspected cause was a defective preheating control unit or a cable/plug issue with the heater module. It was suggested to check the glow plugs, but ultimately, a workshop diagnosed the problem as a corroded connector in the preheating control unit, which was repaired, resolving the issue.
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4 comment(s)
juliuswilliams1 (community.author)
Thanks for the suggestion. I haven't checked the glow plugs directly. Is there a straightforward way to test them without removing them from the engine? Or is it best to just replace them all?
horstfrost1
Testing them in place is difficult. You'd need a multimeter and know the acceptable resistance range. Given the symptoms and mileage, it's probably best to take it to a workshop to have the car electronics diagnosed correctly. A defective engine preheat control unit will cause smoke, the check engine light to come on and the preheating lamp to not switch off.
juliuswilliams1 (community.author)
Appreciate the advice. Took it to a workshop, and you were right – it was related to the preheating control unit. Turns out it was a corroded connector. Repair cost 95€ including labor. Thanks for pointing me in the right direction vehicle heater is working again.
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MERCEDES
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EKLASSE
horstfrost1
I had a similar problem with my E Klasse. The engine preheat system was acting up. Have you checked the glow plugs themselves? A faulty glow plug can sometimes trigger those symptoms and throw codes related to the heating module.