Engine light and preheating light permanently on: Experience and advice wanted for Mercedes SL Class Diesel

Hey buddy, that actually sounds like your ECU could be faulty. I had exactly the same symptoms with my 2011 Mercedes SL Class petrol car. The engine light was always on and the DPF regeneration also failed. Your problem could really be caused by a glow plug, but it's also possible that the control unit is affected. Last time at the garage, they not only had to replace the glow plugs, but also the ECU. It was definitely a serious problem and took a while to fix. So, it's probably a good idea to take it to a garage and get it checked after all. On my car, fixing this problem was essential to prevent further damage. Hope this helps you. Have a safe journey!

(Translated from German)

Hey, thanks for the useful answer! That makes me wonder if the control unit might be affected in my case too. I'm particularly concerned that it could be a serious malfunction that will take a long time to repair. You mentioned that both the glow plugs and the control unit had to be replaced in your car. Can you remember how much that cost at the time? And have there been any other problems since then? I'm bracing myself for the worst and would like to consider everything. Thank you in advance! Have a safe journey too!

(Translated from German)

Hey, no problem, you're welcome! Well, in my case it was actually the case that the control unit was defective. The repair cost €575, but it was really necessary. Since it was done in the workshop, my sled has been running like a dream again! Fortunately, they were also able to solve the problem with the glow plug, so the malfunction is a thing of the past. Since the repair, the car heats up much faster again, even when cold, the misfiring is gone and there is no more black smoke from the exhaust. Everything runs smoothly again. Sure, it was quite a lot of money, but you know - a Mercedes is an investment that needs to be looked after. And to be honest, it's worth the money for me to be able to get back behind the wheel and relax. So, get it checked out, buddy. Better to invest a bit of money in repairs now than to have to pay more later. On that note - have a safe journey and keep us posted on how it goes!

(Translated from German)

Hey, thanks for your input! It's reassuring to hear that you haven't had any further issues since the repair. The cost is quite high, but like you said, a Mercedes is an investment and I want my car to run smoothly. I will definitely take your advice and take the car to the garage and have it checked. I just hope it doesn't take too long to fix it. I really appreciate your help in understanding all of this. Anyway, this is going to cost me a good amount of money, but I'm willing to invest it to make sure my car is in the best shape possible. Thanks again and happy driving to you too! I'll keep you up to date.

(Translated from German)