Car turning over but won't start?

First things first. If the car battery is good and the engine is turning over as normal (sounds normal?) - look at the instrument cluster. If the orange engine management light is flashing, you have an immobiliser issue. It only ever flashes for an immobiliser issue.

Vectra B, Astra G and Zafira were very prone to the key and the remote fob separating -either when in the ignition barrel or even just when somebody is playing with the keys. If they get separated, a tiny plastic transponder chip can drop out of the key and the immobiliser will no longer recognise it.

Very often I've been out to a non-starting car, only to find the chip sat on the mat in the footwell. It's black, just under a centimetre long and slightly wedge-shaped. On later keys they glued the chip in to prevent this.

If this happens on any other model, try your spare key. Transponders sometimes go down and you will need a new one programmed to the car. A locksmith or Vauxhall dealer will be able to do this.

Astra H models required a software update to cure this issue. This will need to be done at the dealer and most would have been cured under warranty by now.

Remote fob not working?

So many problems - sometimes very simple cures.

Vectra B/Omega B with separate fob. Fit a new battery and re-synchronise the fob by turning the ignition on and pressing the lock button. If the fob is working, it will lock and unlock the vehicle.

Astra G/Zafira/later Vectra B/Omega B (fob built into the key). Slide the fob out of the key using a small screwdriver in the slot. Open the fob with the small screwdriver and be prepared for the battery and its holder to fall out of the tiny circuit board. This would normally be time for a new fob - but a very basic fix is to cut a small piece of card or paper and fold it up to sit tight against the battery. This usually maintains contact within the fob and lets you get a couple more years out of it. Again, re-synchronise the fob if need be.

Corsa C. Usually very reliable and probably only needs a battery. Slide it out of the fob, open the fob gently (lugs either side) and replace the battery. Re-synchronise as above.

Astra H. Replacement of the battery is the usual cure but check for any signs of corrosion in the fob which will usually ruin it.

Vectra C. Early units are similar to the Vectra B and the later ones took on the Astra H style. Replace battery and re-synchronise.

If, after replacing batteries, the fobs still don't work, it is worth spraying WD40 over the printed circuit board and wiping it clean. That stuff is absolute magic and has got many a fob working for me again.