My daughter's N-reg VW Polo cut out while driving and won't restart. As far as I can see there is no spark. !2V is getting to the end of the ignition amplifier so I guess there is no trigger coming from the ECU.

There is a fault code showing when the ignition switched on but this is UI 02 which according to the manual means 60 000 mile service is due. But I doubt that a service due warning would be allowed to stop the car on the road.

She said that the car had started losing water and she had to top up frequently.

The only thing I know about ECUs is they are expensive.

1) is there anything I should try replacing first ? Lamba sensor (whatever that is ) etc

2) If I could get an ECU does it plug straight in and fire up, or does it need to be programmed by the main dealer ?

Losing water could be an unrelated problem. Crank position sensor is a common fault, and will stop the engine when it fails...

Does the Polo have a key-type immobiliser? Quite a few of the ECUs have built in immobilisers that will only work with certain keys in the ignition. (Rover, Fiat and Nissan certainly do)....
It'd be worth checking before swapping the ECU (unless you can get the keys at the same time)...

If the lambda sensor died you'ld normally get a specific code for mixture problems.... I wouldn't muck around with the lambda sensor. They're not cheap, its unlikely to be it and they tend to be seized in place due to the material they're made out of.....

It's certainly not going to be the 60,000 service error code. Having a car conk out whilst driving @ 60,000 would be rather illegal (considering you can't do the same thing with tracker remote-immobiliser systems- you can only stop the engine remotely when the car is stationary)....

It's the kind of thing where you need access to an oscilloscope (the handheld ones sold by Maplins are quite nice!!! I had one but I lent it and never got it back).
Then at least you could probe the signal going to the amplifier in real time to see if its getting a signal from the ECU to amplify...

could be a faulty coil pack, if it is the one thats bolted to the bulkhead, they are very common for failure

My Polo Died in the same way. It was the distributor that had failed.

Sisters polo died intermitantly and it was a faulty distributor...

Well, it's not the coil and it's not the distributor. I don't think this model has a crank position sensor - I think that function is done by the Hall Effect sensor in the distributor.

So I guess it's either the immobiliser - I'm trying to get the other key out of her - or it's the ECU -

If no joy on that it's off to the auto electricians.

Thanks guys, as ever, for the suggestions.

Well yes....it wasn't the distributor or the coil. Having taken the distributor cap off a couple of times and tried to start in between, I thought it was odd that the rotor arm ended up in exactly the same place each time.

A light dawned....

Yes, the camshaft drive belt is broken.

Bother !

As far as I can tell, without stripping the head, she's got away with it without driving the valves through the piston crowns, but we'll see.

If she decides to scrap it, there'll be a Polo radiator in it for me

Sounds like it will need a head gasket anyway.

That'll be the one where they change the cam belt then