110tdi Leon occasionally won't turn over

[ChrisG]

Hi All

My missus has an '01 110TDi Leon and in recent months she's had a few occasions where she goes to start the car and absolutely nothing happens. Ignition lights are all on and the battery is fine, its sounds almost as if the immobiliser is still on, but locking/unlocking doesnt help. Ive even got her to take the spare key with her to try that when it happens, just in case the transponder in the key is playing up, but its no better with either key.

The strange thing is though, so far its happened maybe 10 times in the last few months, and every time the fault will rectify itself and she'll be able to start the car fine, sometimes within seconds, other times maybe 5-10 minutes later.

Any ideas? Obviously my concern is that one day it won't rectify itself and leave her stranded, but I can't really do a lot because Ive never been around when its failed to check anything over.

cheers
Chris

 

[Muttley]

Is the starter engaging or not? If no starter, then check the starter relay. The immobiliser will let the engine start then cut it after a few seconds.

Locking and unlocking the car will have no effect on the immobiliser, which is completely separate from the remote central locking and alarm. The immobiliser key is a tiny RFI tag inside your key, a passive component that is read by a coil surrounding the ignition lock barrel.

 

[Pistol Pete]

Hi Chris

Are you absolutely positive that it isn't the battery? Earlier in the year, my Ibiza wouldn't turn over but ignition lights etc came on. Turns out that it was the battery - but didn't seem like it to me.

Peter.

 

[ChrisG]

Hi Chaps

Yeh I wasn't sure quite how the immobiliser engaged hence trying a few different things with the keys etc just to make sure.

The starter motor doesn't turn over no, so it could be the relay but the fact that it will start again 2 minutes later absolutely fine, then not show the problem again for a couple of weeks is odd, if a starter relay fails, in my experience it will fail more regularly than that or need a tap etc to get it going again again.

Anyone know if the starter relay is the same on a Cupra though, because if so I could swap over mine temporarily to see if the fault follows onto my car?

As for the battery, its possible but it shows no other signs of failing, voltage is good without the engine running, it turns over fine and its charging once running.

 

[Muttley]

Probably not. Starter relay is mounted on the starter and I bet the TDI needs a heftier starter motor and everything else to go with it.

How about the electrical connections? Both the power wires to the starter and the earth straps at battery and engine ends. Starter motor needs a lot of current.

 

[ChrisG]

Yeh I havent got round to diagnosing things like dodgy earths, I was rather hoping it would be another case of "just replace xyz component, its a well known VAG problem"