Engine and some electrics cut out without notice

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Mercedes ML270/03/2.7l
I have an automatic car (ML270) and when driving my engine will cut out, power steering fails and the indicators no longer work. No lights light up on the dashboard. I can press the button for the warning lights to come on and that works. I can put the car into park and restart the engine straight away and carry on driving. Mercedes have run diagnostics on the car but no error messages came up.

It almost seems to me that the car has switched itself off as it would when you park and turn off the ignition without having parked and turned the ignition off but when I spoke to Mercedes the problem did not ring any bells.

When we first bought the car this problem was fixed under warranty but only after may be 4 or 5 visits to Mercedes and on the last visit when they did fix the problem there was no note on the paperwork as to what they fixed so I got the impression that they might have just checked connections and accidently fixed the problem.

In fact, this problem has occured twice recently when going over speed bumps so to me it does seem like a loose connection/crossed wires touching.

As the car may be resetting any error messages as soon as I restart the car, the best solution Mercedes have come up with is to get towed direct to them when it happens again without restarting the car, however I am finding this very hard to co-ordinate as for example it happened yesterday en route to pick up my son and I could not just leave him stranded.

In addition, though may be unrelated, every now and again the car won't start first time but says 'error'. I just switch off the engine and restart.

As this is a dangerous problem I would really appreciate any ideas on what the problem is so that we can get it fixed. Many thanks if you can help.
 

Alex Crow

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first guess would be the electrical part of the igniton switch, very cheap and fairly easy to fit so i would have though MB would have done that already - it is a common fault. next would be the circuit 15 relay in the fuse box under the bonnet, suggest you swap this relay with an identical but less important one - such as rear screen wiper - that will at least allow you to rule it out. all relay locations and functions listed in the fuse box lid.
 
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Thanks, I'll try your suggestions

Many thanks for your suggestions. I have already had a look at the fuses under the steering wheel but as they don't match up to the diagram that is stuck inside the cover over the fuses, I am not sure which fuses to switch. When I find my manual I will have another go at seeing if I can swap them. I think I found the Relay 15 you were talking about so that is a good start!
 

Alex Crow

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you do know i was reffering to the fuse box under the bonnet right?
 
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Thanks for clarifying!

Sorry just a completely untechnical woman, I did look under the bonnet first but could not spot any fuses.... definitely need to find my manual! Thanks for clarifying though.
 
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Thanks have swapped the relay switches as first point of call

Thanks, I have swapped the relay switches and if that fails will go back to Mercedes and ask them to carry out your second recommendation. It is so much better to have something to go on rather than 'we have no idea what the problem is', so thanks again for your advice.
 

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