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The car is is currently in long term storage for various reasons. I start her up and drive her round the block every now and again to Check everything is fine.
Just started her up as per normal, drove out of the parking space and switched off for a second and not the car will not start back up.
Im using the key in the ignition slot, i.e. NOT using Keyless Go.
Im getting a brief “key not recognised” message on the dash, the key turns and all the lights come up on the dash as expected, just no sign of start.
So I’m guessing the car has stopped recognising the key. I have a spare key and have tried that, same result.
The car has a virtually brand new starter battery. Only other factor is that the consumer battery is on its last legs, but I haven’t changed it and it’s been on a trickle charger during storage without showing any effects. Currently though as far moved out of parking space Consumer battery only showing 10.5 Volts. I’ve plugged the trickle charger back on for now.
So, anyone suggest any ideas? Would a very low Consumer Battery affect key recognition? If someone can confirm that I have an answer.
Check if the starter relay is clicking on when the ignition key is turned to start. The starter relay is the green one in the fuse box next to the starter battery. Listen or feel for the click with your fingers.
If it works, check you have 12V at the starter solenoid when the relay engages. If you do then it's probably the starter motor.
If the relay is not powering up then it's probably the ignition switch module. Have you run a scan and pulled any codes?
Tom
Last edited by Tom Manning; Jun 27, 2022 at 09:08 PM.
Reason: Incorrect information
If there is enough current ability to power the ignition and lights etc, then there will be enough to energise the starter solenoid relay; those coils draw only milliamps.
You should be able to safely rule out the convenience battery as the cause of this issue.
2005 R 230 SL350 (M112 3.7). Sold the 1966 W113 230SL recently
A battery at 10,5V after having been charged is dead. My concern would not be if an (electro-)mechanical part would work. My concern would be how onboard control equipment would (not) behave in steering the processes.
Even with the battery at very low voltage, or even totally disconnected, the car will start and run.
Essential functions like powering the EIS, ECU and starter circuit are powered by the starter battery (or might be switched to it by the BCM if the rear battery is flat or disconnected).
OP has an issue with the EIS most likely.
Last edited by Tom Manning; Jun 27, 2022 at 04:04 AM.
Reason: typo
Is it just relay L (the green one) in the fuse box next to the front battery that you can hear clicking (that will only be faint - but it may be audible from in the car), or the starter solenoid clicking in? That sound will be much more audible.
If the starter solenoid is clicking in, then you have a bad starter, assuming the starting battery is charged and functional. Check it again. You can jump start the car from another car to the starter battery - not the rear battery. If it starts then you have an issue with the front battery or the car's charging system.
If only the green relay is clicking in then you probably have a bad starter too, but check for 12V at the solenoid when the key goes to position 3.
You might need an extra person under the bonnet to listen in while you try to start it. A bad starter is easier to deal with than a bad ignition key module.
It's good to have a fresh rear battery, but as mentioned that's not the cause of this issue.
Last edited by Tom Manning; Jun 28, 2022 at 08:47 AM.
I’ve already tried jumping the starter battery and it’s virtually brand new. No change
its a loud clicking from under the bonnet when I turn the key. I’ll investigate further as you have suggested but will be next week now as snowed under with work.
Pulled this code off with my Foxwell, which is making me think again about the safety interlock on the gear selector.
No I can’t move the shifter at all, it’s locked in the Park position.
However when I was turning the key and trying to move the shifter, the key locked in the ignition slot and I got the red “put gear-lever into Park” message, even though the shifter was already in Park.
Another clue perhaps that the shifter sensor is failing?
Originally Posted by Tom Manning
Everything with your issue points to a failed starter motor, because you can hear what sounds like the starter trying to engage.
But. That code you pulled sounds like the EIS not getting the security code from the shifter, in which case it wouldn't attempt to crank.
Can you move the shifter out of park easily - repeatedly - with your foot on the brake?
2) Can you confirm that the starter solenoid is definitely clicking in when you try to start? You might need someone under there listening while you try to crank. Should be a loud thunk - hard to miss. If so, then the starter permissions are all working.
3) Put your ear down near the roof switch, and with the ignition on, listen for the click when you push the brake. This will tell you that the lockout solenoid in the shifter is working. It's pretty reliable so it's probably working.
4) If you've got the click then the lockout pawl in the shifter is broken. Don't even think about the replacement plastic pawls - they're rubbish. Buy one of the nice milled-aluminium pawls on eBay - set and forget.
5) Search for the emergency shifter release technique (it involves a hammer and block of wood). Or you can cut the shifter lever and weld it up later - that is what I would do. You have to get it out of park to remove the console trim.
OK, well time to update and………. We have it started! However absolutely no idea how!!!!
My local Mercedes specialist came on a home visit with his Xentry to investigate. Initially the Consumer Battery was really low, we’re talking 6 volts and seeing as it’s brand new that was surprising. After boosting the battery he got his Xentry to connect and read codes which were confirming loss of communication between gear selector and ignition key. He was thinking selector module or maybe ignition key barrel.
Suddenly after 10 mins and lots of key turning the car suddenly worked and started immediately on key turn. We have no idea why. Car has repeatedly been stopped and started since and it’s been fine since.
The consumer battery though is now on a trickle charger but still showing heavily depleted. I can only guess that the problem was caused by an extremely low voltage and once I get the Consumer Battery correctly charged, we should be all good.
A big thank you to all who supported and posted ideas and suggestions
It sounds like you may have an issue with the battery system. The EIS should get sufficient power from the starter battery to enable the electronics and start the car. There is a 5A fuse on the junction box next to the battery module. It is what provides emergency power when the consumer battery is dead. Was your dash coming to life when you inserted the key?
Also, note that trickle chargers will often not charge a very low battery, so that could be why it is not back up to fully charged.
Initially the dash was coming to life but then dying after about 10 seconds. The Starter Battery is almost brand new so following your thoughts, I’ll check the integrity of the 5 amp fuse you suggest. Your thoughts lead me to conclude that even with a very low consumer battery the car should still have pulled power from the Starter Battery, on an emergency basis?
Yes, it should start even with a totally dead consumer battery. A couple of clarifications and other things to check. The fuse I was talking about is actually a 7.5A fuse. It provides emergency power to the EIS, ECM, and SCM, but I'm not sure if it is necessary to wake up the car. You should also check F52f1 and K57. K57 is mounted right next to the BNS and is what actually connects the two batteries for emergency operation when the consumer battery is too low. F52f1 is a 100A fuse in the wire that connects the starter battery to the BNS (the power feed for emergency operation). If either of these two components is not working, you have no emergency power function and a well charged consumer battery would be required to start the car and both are fairly common issues.
