Electrical fault?

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derekpayne

Active Member
Joined
Dec 17, 2011
Messages
78
Location
Torbay
Car
CLS 320 CDi 2008 "Facelift"
Hi,

My CLS 320 2008 developed a strange fault today, first of all the alarm went off for no reason, then the horns were sounding constantly, I opened the car, turned the ignition on and they stopped, I turned the ignition off but then it wouldn't let me turn it back on again and the gearstick was stuck in park. I disconnected the battery, connected it back up and was able to turn the ignition on again, but once I turned it off it was stuck again, remove the key and put it back in and without turning it , the ignition is on, remove the key and the ignition is off. I disconnected the battery again, started the engine and moved the gearstick to neutral started the engine, but when I turned the key to the off position the engine still ran and even when I disconnected the battery it still ran, I had to remove the fuel pump relay to stop the engine.

What the hell is all that about?
 
Could be low battery voltage issue. Mercs do not like low voltage and will throw all sorts of hissy fits. Disconnect the battery and charge it fully. Then try again, how old is the battery ? 3-4 years is about average life these days, Mercedes have lots of toys that need good voltage.
 
yes thats the first thing that sprung to mind for me too, checked the voltage and it was 12.4 volts, a bit low i thought so I've put it on charge for now with the battery disconnected and will check it again tomorrow.

I think the battery is the original as I've not seen any paperwork to suggest its had one, which means its been there since 2008.

If anyone else has any ideas they would be welcome

Cheers
 
My W209 2009 is on the third battery at 123K short journeys are a killer. This time Ifitted a Varta EFB seemingly they hold up better for short jouney work.
 
yes thats the first thing that sprung to mind for me too, checked the voltage and it was 12.4 volts, a bit low i thought so I've put it on charge for now with the battery disconnected and will check it again tomorrow.

I think the battery is the original as I've not seen any paperwork to suggest its had one, which means its been there since 2008.

If anyone else has any ideas they would be welcome

Cheers
There will be a date stamp on one of the battery terminals .
 
Do 2008 cars have the same dodgy alarm sounders as 2006 ones ? If so just un plug it and see what happens . They are notorious for back feeding into the car when the internal circuit/batteries rot out causing all sorts of very odd faults.

It's unlikely , but its a cheap an easy check to do.
 
Right then,

I charged the battery for approx 24hrs, now showing 13.6 volts, and the majority of the faults have disappeared, I will replace it as I think its been on the car from new, 2008.

The problem I have now is, no glowplug light, no engine crank over and no OBD diagnostic port comunication, either I have done something yesterday to create this fault or a fuse has blown, ive been checking all fuses but cant find any gone, what I really could do with is a easy to read fuse/relay diagram as the Merc one is a bit vague to be honest.

Anyone got any ideas and/or fuse/relay diagram?
 
If there is diddly squat happening, try checking the fuses located under the bonnet, just in front of driver, hidden underneath a couple of covers (assuming similar layout to the W211).

When I had the W211, it once developed a fault where basically nothing seemed to work and engine wouldn't crank. Turned out to be a 13A fuse, where I just tried describing, that had blown. Initially, we were thinking dead battery, starter motor, etc.. but it was a blown fuse.
 
You didn't short anything out when charging the battery did you ? Are all the secondary supply leads connected back up to the battery.
 
Haha, some t-w-a-t (me) whilst checking everything yesterday, removed one of the relays in the fuse/relay box under the bonnet and fitted it back in the wrong position, whilst trying to find this fault today I tried it in the different position and everything works fine now, learnt a valuable lesson, don't put things in the wrong hole as it doesn't work!!
 
Haha, some t-w-a-t (me) whilst checking everything yesterday, removed one of the relays in the fuse/relay box under the bonnet and fitted it back in the wrong position, whilst trying to find this fault today I tried it in the different position and everything works fine now, learnt a valuable lesson, don't put things in the wrong hole as it doesn't work!!
Lucky it was only on the car, you might have got a slap otherwise!😉🤣
 

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