Could this really be a flat battery?

[Nidge]

I hope the collective wisdom here can help me. Last night my E240 (W210) wouldn't start, just emitting a click from the solenoid, however the lights remained at a constant brightness (interior and panel lights) as I tried to crank the motor, so very unlikely a flat battery (I thought). I called the RAC (no Mobilo life on the car due to using independents), the patrol man was equally confused by the the fact that the interior lights stayed bright but attached jump leads to the terminals under the bonnet and lo and behold the car started on the first turn of the key.

I'm 80% convinced it's a battery but for the lack of dimming/reduction in power of the ancilliary electrics. Any thoughts?

 

[tom7035]

Sounds to me like a terminal problem (electrical terminal, not the death knell of your car!) Remove battery terminals and thoroughly clean and rub-up with emery cloth. Replace and coat with Vaseline. Check and clean the earth lead to chassis and chassis to engine, and the connections at the starter solenoid.

 

[philharve]

Hi Nidge

I experienced very similar symptoms with my C230K last year during the cold spell. All interior lighting was fine but when I tried to start the car all I heard for a 'click'. The starter motor didn't even attempt to turn the engine. I thought of battery or starter motor problems and/or dirty/damp connections between the two.

The problem was the battery. My indie diagnosed the problem over the 'phone which was subsequently proved to be a 'dead cell'. I replaced the battery and all was fine again.

But why didn't the starter motor turn? Aparently it is a feature of the Mercedes that it won't start if the battery's voltage falls below a certain voltage, believed to be 11V. My indie informed me there is a sensor in the car that prevents the battery being flattened using the starter motor. The sensor ensures there is sufficient current remaining in the battery to run life support systems: lighting and heating.

It may be this sensor that is overriding your attempts to start the car. Simple solution, use another 'good' battery to start your car. You need to put sufficient charge back in your battery to raise its terminal voltage above the 11V. When it happened to me I used my brother's car to charge my battery for a few minutes. Once started, get to your dealer, indie, motor factor outlet and get your battery 'professionally' checked. They have equipment capable of detecting battery faults. Don't rely upon a domestic multimeter, if you have one, to diagnose the problem.

If it is a dead cell, your battery will let you down again, and when it's most inconvenient. Sods Law. Get it replaced ASAP.

PS - Exercise great care in connecting batteries in parallel. Sparks can ignite battery vapours with explosive results. My battery is in the boot of my car, a confined space. I made sure that when I connected my brother's battery in parallel with mine the connection point was well away from my battery. I used 3 jump start cables. Connect 'positives' first.

REGARDS Phil

 

[jberks]

Mercs are very fussy about voltage. If you don't have the correct voltage, it won't even try to turn over. So, the lights may come on and everything look ok, but it may not turn over. Had it on the C220, wouldn't even go with jump leads. Put a new battery on and she jumped into life.
Try a new battery.

 

[Nidge]

Thanks Philharve, I did wonder if there was a sensor that prevented any draw taking the battery below a pre-defined voltage and he fact that the car started perfectly with jump leads would seem to confirm that everything else is working.

Once again thanks for the comprehensive reply

 

[philharve]

Thanks Philharve, I did wonder if there was a sensor that prevented any draw taking the battery below a pre-defined voltage and he fact that the car started perfectly with jump leads would seem to confirm that everything else is working.

Hi Nidge

Glad you got the car started.

Will you have the battery checked because you might have a sick battery?

REGARDS Phil

 

[bundy]

hi nidge
deffo the battery at voltages much below 12.2 merc control units seen to get confused. i had a cl500 amg in the workshop last week with all manner of fault codes both stored & current when i read these 99% said undervoltage codes. it only takes 1 cell!!!
regards ted

 

[television]

Everyone is right on this one, when the voltage falls on newer cars to 11.7 it normally cuts off all aux; items, at anything less than 11.7 the starter relay cant close, the clicking you can hear is that relay normally and not the starter solinoid. Not all cars have a starter relay, but it does make a good isolation point for the alarm.

Malcolm

 

[Nidge]

It gets worse...

OK so new battery fitted and it started immediately, revved cleanly until I put it into gear. It now wont rev cleanly, occassionaly managing 4,000rpm before sticking at 1500rpm and very very lumpy. Anyone able to help at all?

 

[bundy]

take it for a run. about 20 mins it should sort itself out!!

 

[Nidge]

Thanks for all your help on this one guys. Leaving the battery disconnected for 15 mins didn't cure it but the supposed ECU reset trick (key to position 2, throttle to the floor for 5 secs, key off throttle release and wait 2 mins) semed to have some improvement the first time I did it and lots of improvement the second time- the car would now rev to 5,000rpm and was driveable. 20 mins later all functionality seems to have been restored.

Once again thanks for all your help.