CLS55 AMG - No start/No crank

[ScottJB]

Hi all,

Apologies for making my first post on here a problem post but the guys over on Pistonheads recommended this forum. Love the car, except its stuck on my driveway going nowhere fast as it stands.

Background - fairly new owner of an 05 plate CLS55 AMG. When purchasing the vehicle, the prev owner mentioned he had a no start breakdown. After calling out Mobilo, the tech ended up opening the box just in front of the driver at the top left of the engine bay (front SAM?). The prev owner said he pushed the relays down and the car started. Theres a receipt in the history file for the car that tallies with this story.

Fast forward to my ownership. I've owned the car about a month. I huess ive had to start the car the best part of 100 times during this period. Twice i've had to repeat the previous owners advice. Twist the key and no attempt to start, dash lights on as normal. I've then opened the bonnet, fiddled with the fuses & relays in the front SAM and got it to start.

Today - same situation. Twist key and no crank, no start. I did however get the message "Battery protection : convienience functions temporarily unavailable" and "ESP Display Fault Visit Workshop". Ive tried to jig around with the relays/fuses in the front SAM as per previous "fixes" but no joy thus far.

Thoughts

- Battery message got me googling. The secret menu (put key to pos 1 and press the reset 3x) says i have 11.7v. This sounds too low? Boot battery dead?

- Although many searches mention the CPS. I dont think it fits my symptoms as when my car has had this issue it doesnt crank at all and the issue doesnt seem heat related (car has not been started today so is stone cold)

- Why has fiddling about in the front SAM worked before?

Any help/advice greatly appreciated

 

[herby thr cls]

11.7 V is a dead battery, renew the battery, and you never know the relay problem might be connected to low voltage as well

 

[Gareth]

Sounds very much like a battery issue, its an 05 (ten years old) mine is a 55 and I had both batteries replaced on its last service to avoid such issues (I had Battery protection : convienience functions temporarily unavailable messages during cold months)

 

[ScottJB]

Cheers guys. Sometimes the obvious answer is right - just pulled the main battery out and stuck the charger on it and its well into the empty part of the gauge. I'll try to bring it back to life overnight, if not i'll pick a new one up. Then if it fires i'll check the voltages in the hidden menu whilst off/running - hopefully the alt is fine.

Checking my receipts it looks like the secondary battery was replaced last year.

 

[ScottJB]

Update (and current resolution for the benefit of someone in the future having the problem)

Charged battery overnight. Hooked up and tried to start. Same result as yesterday. Checked the battery voltage in the secret menu and 11.9. At this stage i was resigned to going to get a new battery

Thought i'd have another fiddle around in the front SAM. Worked through the relays one by one and found one that could be considered loose. Looking at the diagrams this relay is the Terminal 87 relay, Engine (N10/1kI). See relay I below.

Pushed the relay back down and slightly angled towards the wing. Got back in the car and accessed the battery menu. Now showing 12.2/12.3v off. Twist key and the car starts. Running voltage is 13.9/14.0 idling with Command on. Does that sound about right?

In the interests of then repeating the problem. I moved relay I in to a more straight up position and the car wouldnt crank. Angled it slightly towards the wing again and the car started.

Conclusions?

- Relay I definitely isnt seating right for whatever reason. I'm inclined to buy this relay new from Merc and hope the new one fits more snugly on the terminals.
- Battery might just have been low coincidentally at the same time i'm getting this relay issue. I guess i'll just monitor the voltages

If anyone has anything to add/wants to disagree please shout

 

[John]

The off voltage still sounds too low to me.

On the plus side - it appears your alternator is working fine!

I would give it a nice long run (not just a quick 10 minutes) and post up what the off voltage is then.

 

[ScottJB]

Further update, to close this out if anyone is searching similar symptoms in future. Car needed the front SAM unit replacing. Tow (doh!) + Diag + New unit from Merc + labour at Indy (Mercare) = £700

 

[Amo]

I have always monitored voltage on my 211 and 219 (mainly because i use to run alot of aftermarket audio from stock battery) I have never seen battery voltage above 12.2 when testing from hidden functions (when cars off), when you turn the ignition it will then drop to below 12 and when cracking it will drop to high 10 or low 11 volts before starting and stabilizing to 13.9 - 14.2.

 

[markmifsud]

Wouldn't it have been cheaper to investigate why the relay wasn't sitting correctly in the socket. Could have just been some corrosion on the socket terminals.

 

[ScottJB]

Amo - useful to know mine sounds the norm for displayed battery voltage then.

markmifsud - Mercare carried out the diagnosis & repair. Car was towed there (after the relay wiggle failed to resolve) and left with them. They advised a replacement front SAM was needed and i went with that. TBH after reading similar threads online i was just pleased it wasn't the ECU that needed replacing. I was happy with their service to be honest and the guys there seemed very clued up. Steve was a gent. I had got to the point i couldn't trust the car to start everytime i parked it and was happy to know it was sorted properly albeit at a bit of an expense. Electronics aren't my forte unfortunately.