Immobiliser intermittently not arming
 

I think last week's awful weather locally might have affected some of the electrics on my S40. Did a lot of mileage last week in very heavy rain and through lots of surface water. Noticed when locking up one day that my hazards didn't flash, and that the immobiliser light on the dash stayed out afterwards, and wouldn't flash.

I pulled out the engine bay fuse for the immobiliser which I wasn't expecting much luck with (one of the cuboid shaped ones, 20 Amp) and noting it looked okay, put it back. To my surprise this reset it and the immobiliser worked fine again, checked several times. A couple of days later it faulted again, and the same 'fix' cured the fault, for now.

To clarify, there's no issue starting the car as the immobiliser disengages as it should, it just doesn't want to arm sometimes... anything typical to look out for or should I just hope it dries out... assuming it's even water that caused it to begin with.

On both of my phase 2s I've had an intermittent connection on the bonnet microswitch cause this problem, I can't remember exactly what I did now but in both cases it involved some precision bending of the thin metal contact strip so when the bonnet is closed it actually makes full contact with the push in part of the switch.

EDIT: found my old thread with pictures that Gatos very kindly added.

https://www.volvoforums.org.uk/showthread.php?t=280403

Interesting! Wouldn't have thought of that, so it's more than likely nothing to do with the fuse I was pulling, just opening the bonnet may well have temporarily cured it.

I'll have a look this weekend when I have chance, and report back... thanks again

Update... right on the money! Messed around with it and it's apparent there's a problem with the switch, not just the arm. Appears it's been changed or removed at some point and not put back properly as the wiring to the plug was not properly secured or weatherproofed...

Is there a part number readily available? Just wondering if FRF might be able to help providing it's not too much cash...

Cheers for the heads up

If you're not overly fussed about it the switch is a push to make circuit type as opposed to push to break, so you can just unplug it and bridge the connectors on the loom with something like a paper clip or a small piece of wire with spade connectors on.