Sprinter tries to start itself with no keys in ignition

[Jenni Newman]

Hi all



New to the group, bought a 2014 MWB sprinter 2 months ago to convert in to a camper.



The battery was a little weak so charged it via the jump start terminals this morning. Battery charger said it was connected to battery and left it to do its thing



3 hours later, the van starter motor begins to turn along with the windscreen wipers and the windscreen washer jets.



Put key into ignition and tried to turn ignition on and off but with no avail, starter motor continued



Couldn't stop the starter from turning the engine so disconnected battery (around 3 or 4 mins had elapsed at this point), strong smell of burning cables and dead battery (and possibly starter motor too)



All electric appear to be OEM, no hacking of new cables anywhere that i can see



Anyone got any idea where to start with this ? Checked and it appears as though the relay is on the side of the starter but if there was no key in the ignition, would the cable that feeds the relay be powered at that point ?



Any help appreciated... partner v upset



Thanks in advance



Jon

 

[joderest]

I think, but not sure, that started main feed is direct off the battery, however, the solenoid should be ignition switch controlled.
did you leave the bonnet open whilst charging ?, could well be that rain water has found its way in some where causing a short circuit.
I must admit i am guessing, i am sure someone with more knowledge than me will be along soon.

 

[rpalmeida]

Theres a starter relay, possibly it is failing. The starter relay drives the solenoid that is on the starter itself (via the thinner wire (possibly purple). The starter also has a fat +12v from battery. Starter relay in main fuse/relay box Relay 5.
The starter relay (generally on all Mercedes, havent looked at Sprinter specifically) is driven from the engine management system and/or the front SAM.

I suspect its the front SAM on your car as that also controls the wipers and washers .. and that its telling relay to come on. But just a guess.

It is likely you are just smelling a very hot starter motor, but given hot means fire and melting, I would not re-connect the battery, get it recovered to a specialist who can work it out.. Warn them about the burning smell etc before you take it to them, they may not want to touch it.
If you were going to ignore my advice, I'd remove the starter relay before connecting the battery, and have someone ready to disconnect the battery if something smells hot, and have a fire-extinguisher around. But really diagnosis of such faults requires times and Xentry Diagnosis

R

 

[M80]

If your fuse board is A639 545 0401, embossed into the plastic casting, toward the front of the van, then I can help with relay identification.

I would pull the starter relay and wipers relay, washers aren't fed via a relay. When charged I would touch the battery lead to the terminal to see if anything happens.
If nothing happens then insert the wiper relay to see if that's still as on, then perhaps the starter relay but being ready to pull them.

Much as above it sounds like the SAM is goosed, they don't like water if it has got in. If it's like the Vito / Viano the ECU and TCU are in the same enclosure.
If there is possibility water has got in there I would want to get those electronic units out as soon as in the hope they can be saved.

 

[mioba]

Did u try thumping the starter motor

 

[Kev555]

As above in a couple of posts I would suspect water in SAM

 

[DREAMER NO2]

The only time this ever happened to me, was years ago just after i had passed my test . Not knowing any better i put some grease on the ignition key to help it in and out the ignition lock . I know poster has not done this but i would check ignition switch first . A fault in there would start the ball rolling .