1.9TDI fabia elegance estate 2005 occasionally immobilses engine for no apparrant reason. Key opens everything as does remote control, but engine spins and won't start. If its's left for several hours then it starts.

Have I pressed too many buttons and there is a reset priod or is there another problem?

Any help much appreciated, because it has stranded me twice now.

Extra extra.....!!!

Finally the car restarted took it to dealer, who changed the fuel pump relay.Costing no alot.

The dealer and I were not entirely convinced that this was the problem,but the car ran faultlessly until yeaterday 7.8.11. Once again engine turns no start. Fortunately on the driveway!

I went and bought two new fuel pump relays,so I could carry one in future. My dealer still not convinced this would cure it. No doubt getting a bit fed up with me bothering him, but they are very busy and good.

Spent part of yesterday and today with half the drivers side off checking connections around the panels,tried all the relays that I now have, nothing.

Then read about speed sensor/cam position sensor preventing engine start by not enabling the fuel pump relay and thereby the fuel cut off valve/immobiliser. I was preparing to remove the sensor when I found that the connector was not snapped shut,(about 1mm to go) . There is similar connector on the same bracket on the front of the engine near the top of the oil filter.So I took them both off (they slide out of the mounting),tiny squirt of WD40 and replaced all. I heard the fuel relay click as I switched on and normal start. My cheer heard above the engine noise! The speed sensor is the culprit, either the sensor failure or in this case the connection.

Just to prove the issue I even put back the original suspected fuel pump relay and the engine starts every time.

You won't get any error info on this or any lights because the initial pre start checks to the ECU are ok and it doesn't show this as a fault because ecu is programmed to accept the fuel pump being cut by the immobiliser circuit anyway. The engine will not be stopped by this fault occurring once it is running,but if it is stopped it will not restart.

Edited 6 August, 201114 yr by SKODASGOOD

Does the yellow immobiliser light flash when it fails to start?

It could be the key (unlikely, but worth trying the spare), the reader coil/wiring to it, or the instrument cluster. I have changed a fair few dashboard with failed immobilisers one of which I remember was a 02 plate Fabia not too long ago. Instrument clusters are around £50 and I can code them in for you and correct the mileage to what they should show.

Thanks for that.

No immobiliser light flash. All other dashlights come on and go off as norm.

Tried changing keys at the time and still no start.

The battery was still spinning the engine well, but I noticed in the manual that low voltage can affect the security systems and the car had been lots of very short journeys all week.

Car started after about 3 hours standing and a short battery charge.

I left the car on charge all night and it was taking 3-4 amps.

With no flashing immobiliser light it sounds like a fuel delivery problem. Do you have any fuel leaks anywhere?

Replace battery. Not enough crank revs for fueling.

Thanks very much for the suggestions.

The problem has re occurred and left me stranded twice recently. Engine turns over,but no start.

Sometimes the SRS light comes on,but the engine managemant light does not.

Leaving the car and coming back to it 30 mins later made no difference this time.

I Really like the car and it has been the best ever for lots of reasons,but either I cure this or it goes,can't trust it like this.

So disconnected the ECU and reconnected no effect.

Removed instrument panel and re connected no effect.

Ran a diagnostic fault code check, no codes.

Thinking about low battery voltage,put a meter on it,but was showing 12.78v after everything on and 14.9 when charging on idle.

The battery is the original and now at least 8 years old.

Glad I didn't go for a new one!

One last major look at the relays,real pain to get at them.

This time I took the heavy cable holder off which is in front of the relay board to give better access,just one large torx screw.

I took all the relays out and replaced them(so I thought) no effect.

Then contrary to the book,removed and replaced them with the igntiton on.

As I replaced the large bulb sensor/relay,l(ots of beeping when it was out)there was a click and the engine management light came on,engine started.

The click was not from the large bulb sensor.

By moving the sensor a bit I could get the engine management light/ engine starting to come and go.

Another relay ?

Tucked in the corner behind the bodywork is the fuel system relay 469 black with 4 ordinary blades and a small one .5 total.    part no 6Y0906381

Seems this also feedsback to the ECU as well. It is a VAG/Skoda spare only.

I removed the relay case and the contacts were badly pitted,it would seem that the relay needs to reset when the igniton is turned off and it wasn't. I cleaned the contact with a nail file and replaced it,the engine started every time with all the warning lights showing as the igniton was switched on. Then just the engine management,charging/battery and hand brake,finally leaving the hand brake after the engine started.

Obviously I have replaced the relay.

The moral is find the right relay! The one I changed in ther previous post wasn't the fuel sytem relay Doh!!

Interestingly, when I rechecked the fault codes there were sveral caused by my live relay removals including one for ECU with wiring,fuel relay or fuel system as the possible causes.

Keeping the car and carrying a spare 469 relay.

Edited 29 December, 201312 yr by SKODASGOOD