Odd one...

[TechNick]

Would welcome some ideas on how to resolve this one...
Electrical issue of some description.

Battery and alternator are relatively new and both appear to be functioning fine (based upon the voltage guage).

Car fires up fine if sat overnight or left for 45min+ since last use, and also fires up fine straight after reconnecting the battery (if had been disconnected for some time whilst in storage).

Issue arises if you try and start it after a few minutes from stopping it (e.g. a petrol station or popping in to a Shop).

You turn on the ignition, everything lights up and makes the noises it should, volt meter rises to just over 12V, but nothing... starter motor doesn't even try to turn or click.

Through trial and error, seems if I leave the car parked up for 45min or more, it then fires up fine.

VCDS seemed to show the immobiliser was being turned off correctly with the key, but acts like it's immobilised.

I even tried putting a fresh battery in my spare key and reprogramming that back up successfully, but won't start up with that key either, during that 45min dead zone.

I did have a probably related issue several months back. Starter motor would work, though, but just buzzed - like it had jammed/wasn't getting enough juice.
I replaced the related relay(s) behind the knee bolster area of the dash and it seemed fine after that.

I tried pulling and swapping those same relays when this latest issue arose, but didn't seem to help.
Disconnecting the battery for a few mins didn't seem to help either.

Only workaround seems to be to leave it 45min or more.

Presuming some sort of capacative charge remaining where it shouldn't be, which dissipates over time, but don't really know where to start to look to rectify it.

Any suggestions?

[TOPMAN]

I’ve had a similar problem to this in the past. The starter was old and suffering from heat soak. Had the starter rebuilt and it’s been fine since. Manually apply power to the solenoid and see if she works, if not then you’ve probably found your issue


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[Shoppinit]

Sounds like the crank position sensor. Quite common failure and symptoms like yours.

Doesn’t give any fault codes. Cranks but just doesn’t fire.

[TechNick]

I’ve had a similar problem to this in the past. The starter was old and suffering from heat soak. Had the starter rebuilt and it’s been fine since. Manually apply power to the solenoid and see if she works, if not then you’ve probably found your issue


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Thanks. Hoping it isn't the starter, as it's not very easy to get to on these, from what I understand (not that much is, of course!)

[TechNick]

Sounds like the crank position sensor. Quite common failure and symptoms like yours.

Doesn’t give any fault codes. Cranks but just doesn’t fire.

Thanks Ben.
It isn't cranking at all, during that dead zone period, though - turn the key and nada

[Shoppinit]

Oh. My bad. That’s a completely different problem then.

Immobiliser won’t stop it cranking.

Check the gearbox with Vagcom to see if it thinks the selector isn’t in P.

Check the 200A fuse in the scuttle.


Get a LED or multimeter on the starter to see
If it’s getting a signal to the solenoid.

Check the brake light switch. Belt and braces.

/my gut says starter motor, but that’s possibly because I’ve got them on my mind because I’ve a similar issue with the M3.

[TechNick]

Thanks. Few things to try!