colt

Hi all ,I'm new on here and hope that i will find an answer to my problem.
A 2005 (55 plate/UK) C220cdi T model has an intermittent starting fault.
Only when it's cold out (around 0 Celsius ) The ignition can be turned on and all functions are working (lights ,wipers horn ,heating etc) when you crank and start the engine It starts but the instrument cluster fails to read the rpm, the windows are inop along with the wipers ,heater, and lights and other systems. Quite often you can just switch off and restart and within a number of attempts the systems will "wake up" and work after starting as well as before you start to crank it over.
It seems that the battery voltage is dropping too low upon cranking for the control modules affected to wake up, but the battery ,charging output are fine and the engine doesn't even sound slow to crank when it happens, Never seems to reoccur after it's come back to life until the car has completely cooled down again (8/10 hours plus) sometimes it takes two or three starts and stops before it wakes up and when it's really cold (minus 5) it may take twenty or more ,and this is starting it and if the rev counter fails to read,stopping it immediately and restarting again . So in twenty starts, not much if any heat has got into anything because you can do this in a minute or two.If the systems don't wake up straight after starting ,they aren't going to so their is no point in letting it idle away. Having said that you can get the same result from starting once and letting idle for ten minutes and then turn off once and restart and everything is "alive"
Is their a known issue with a green connector block or control module software upgrade to stop it looking so hard at battery voltage when cranking? I think that it's too sensitively set so that the slightest low battery voltage at crank turns some circuits off?

Circuit 15 and 15r relays have been changed in the front sam F along with the front sam itself and the eis control unit.
Their are also 15 and 15r circuit relays in the rear sam but that as yet has not been touched.



Help! Colt

Carsy

How old is your battery ? If it is original it may time for a new one.

I have read on this forum that the 203 is susceptible to computer problems when an old battery is fitted.

You may be able to test this by jumping from a battery pack or another car but make sure the key is off & out when connecting up. Do not fry your SAM.

A battery load test by an auto electrician is probably the safer option.

Good luck.

colt

Thanks for the reply, i have fitted a new battery to try that ,last week when the weather was cold and it did not improve the situation,even though the old battery is the original!, | have been told by a mecedes benz tech that he has known a faulty key give this fault,( the clue according to him was if the computer display was still active inside the instrument cluster when all other gauges on the cluster were dead) and that is the case!I was advised to try the other key, only the car was supplied with one, so that cheap fix is not available!

Cj

Carsy

It is a good idea to have two keys anyway, so you may have to bite the bullet.


Please let us know how you go.

JC

SunnyRayToronto

Double-check fuse #52 in front fuse box under the hood (where you will also find relay and front SAM),.... make sure its upgraded 20 amp and not 15 amp.

colt

Well all, after looking a bit deeper in to the can systems with a xentry diagnostic system. In specific can tests, and under a sub system their is a note about what diagnosis path to take if the can system is down and circuit 15can,15r can and 15 c can are switched off,(which you can check in actual values) and this was the case when it was faulting. It says "if this happens shortly after starting try the other key"
so it's would appear that it's a known issue. Ordered and received a new key and by chance it was frosty that day and i would have expected it to fault.|Tried the new key and it was fine. time will tell but i think that this was the root of the fault. Still can't understand how the key can work remotely fine ,switch to ignition on fine (all systems active),then start car and can circuits fail to reawaken? key is obviously matched to the car immobilizer wise otherwise it wouldn't even turn in the lock let alone start the car. It's as if the key has several immobilizer chips in it and only one has failed. it would have been far more obvious if the key had gone totally dead!But at least if fails in this way it wont leave you stranded!. I do wish i had explored all the guided fault finding paths on the xentry before i fitted a new ezs and front sam. would have saved a chunk of money .
I know now ,always try a new or alternative key first!!!!!
Cj

Carsy

Thanks for the detailed update. Good diagnosis. Where did you find this information?