copterguy

I posted this elsewhere, but wanted my 218 peeps opinion.
Any ideas as to what this issue may be? My 2012 CLS63. Battery voltage good, even with jumper cables on just for a good measure test. The car will not start when I push the start button , but the clock spins like it's resetting, lights and radio turn on, even after turning radio off. Check terminal connection to battery is tight. I did get a check engine light the day before, fuel pressure too low, reset and it ran fine after.. Maybe. I'm guessing the connection to the fuel control may be an issue or the fuel controller itself. Thoughts? Just odd that it would spin my clock, geez. I do have a tune on my ECU, could it be an ecu problem? Wondering if anyone seen this issue and has a surefire answer.

6speeddave

Make sure the main battery is an actual AGM battery first. You could also check your auxiliary battery in the trunk. Tune shouldn't be the problem and the clock resetting is a sign of the electrical system getting low voltage or voltage fluctuation causing it to reset. I would check the alternator voltage regulator OR plug the car into DAS and have a mechanic check for fuel faults. Hope this helps.

copterguy

I thought the main battery was the one in the trunk? It's an AGM for sure. I am looking at the auxiliary battery in the front, smaller, don't know if it's AGM, but I stuck a charger on it, shows low...

6speeddave

No, the main battery is in the passenger side of the engine bay near the firewall. The trunk battery is the auxiliary. Both should be AGM.

copterguy

Lawd, I've been backwards for a few years then. I had a CSL55 and this Car, even started both from the battery in the trunk, and it would start. Thanks, I'm gonna check the main battery now....

6speeddave

The battery locations and sizes are very different from the prior W211 / W219 chassis', yes.

6speeddave

I am 95% confident the main battery is your issue. When was the last time your main battery was changed?

copterguy

Ha, that would be, Never. I hope you're right, I can do battery replacements...any idea of where to get one other than the dealership? I avoid those places. I was just online looking for options on that...

6speeddave

Do you have Pepboys in Hawaii? They have a BOSCH brand battery that is solid and its less than $200. May even be able to use an online coupon code to save money online then just go pick it up. Just make sure they give you an AGM battery. When I picked mine up for my E63 last year they gave me the wrong one and I didn't realize it.

Replacement is straight forward. Pop the blower motor housing out and then there is one bolt / bracket that holds the main battery in the engine bay. Unbolt that and it pulls right out.

copterguy

NO Pepboys in Hawaii. O'Riley auto parts or online, there's a couple of local Euro shops. Do you know the part number or link to that bosch battery?

6speeddave

I dont, check out their website and put your vehicle info in and it should be the only option in AGM.

I wouldn't go O'Reilly's unless they carry Interstate. Someone local with a good brand is your best bet in case anything ever goes wrong with it and its covered under warranty.

copterguy

Thanks for your help. It was indeed the Main Battery. I got another at the MB dealership, cause not many other options on this island. cost about 310.00.

6speeddave

Sweet. Now you're good for another 5 years!