Can / does the immobiliser cut the engine during normal driving?

Cinquecento Sporting, 1998.

The engine suddenly cut out on the dual carriageway.

Wouldn't start at all.

Checked the new TDC sensor as the other new sensors had failed nearly straight away, but that seemed OK.

Did some more continuity testing and found there was no voltage to the coils; unplugged, the blue wire / green stripe, should be at 12 Volts, comes from the white relays module near the ECU. This wire seems to also feed Injector, Lamba, Purge valve.

I ascertained that there are the three permanent 12 volts feeds at the supply pins to the relays from the 20 Amp fuse under the black cover behind the ECU, and a switched voltage supply from the ECU (or immobiliser?) to pin 12 of the relay module (supplies the coil that feeds the blue wire / green stripe).

Seems one coil might not be operating. So I removed this white double relay module and tested with my bench power supply and meters and all seems well in there.

Having removed the ECU, I traced the continuity from the relays plug to the ECU plug, all that seems OK. With the ECU still removed, using wire leads I made up, I tried to energise the 'blue wire coil' with a +12V to one side (relay pin 12 via ECU pin 6) and earth to the other (relay pin 7 via ECU pin 23) but before I applied the +12, with just the earth fitted, there appeared +12 at the coils blue wire and something in the throttle body made a constant whirring noise. I checked the pins twice and I can't explain why they powered up with no +12 feed to the coil and just one side of the relay coil earthed.

What do you all think about this weirdness?

I'm wondering now if the immobiliser is the cause of the engine shut off as the only thing joined to that relay coil feed (relay pin 12 / ECU pin 6) is the immobiliser. So was that supplying the power during the test and not supplying during normal running?

So what actually happened when it cut out? Did the key/code light come on on the dash? If not, it's not the immob. Have you reset the fuel cut off?

I was going down a dual carriageway hill at about 40mph in traffic and then there was a bit of a mild boomp and power cut off. Engine was still making some running noise as it was still turning over as I was still in gear and had momentum down the hill, but not actually under power. I realised it had conked out and dropped out of gear and I coasted about 1/2 a mile and stopped in a right turn slip road at the bottom. I tried to restart it a few times on the way but it was not responding.

Don't know if the imob light came on. Didn't look.

No to the fuel cut off. What and where is that?

Sounds like the FPS has cut in, it's meant to do it in the event of a shunt but has been known to happen at other times too. Search the forum for FPS as I can't remember exactly where the switch is (I've also never hunted for it in my car, I really should though!).

I don't that that's the fault as there's appears to be no fuel pressure sensor or any way for the ECU to detect that has switched off the pump.

If that so, that can't cause no voltage on the wire to the coils, nor can it cause a supply voltage to the coils when earthing the relay pin 7.

Re: Can / does the immobiliser cut the engine during normal driving?

Checked all the earths? Engine to chassis ect

I only found three.

One from the back of the coils end of the head, under the leads plug bracket. Though that maybe going TO the earth.

And one each side onto the wheel arch.

With the multimeter, the rocker cover is about 0.1 Ohms to the battery negative lead. ECU also.

Can you tell me where that are more?