Immobiliser Troubleshooting

[V28VX37]

Hi all, I've got an aftermarket immobiliser in my R34 GTT that has all the usual features like keyless entry, turbo timer etc. I've had it for several years.

I've been having a sporadic but severe issue with the car over the past couple of days: I sometimes cannot disarm the immobiliser at all. The alarm light (the little blinking led) goes dead and it doesn't react to remote in any way. I also cannot start the car with the Nissan key, it doesn't even crank. I also had the car stall on me once when stationary, which is pretty annoying in an auto. Again it wouldn't deimmobilise straight away but I finally got it going.

I think my battery was on it's way out anyway so I bought and installed a brand new battery today, with slightly higher capacity too. I drove the car for a bit after installing it and it cranked really well. However, when I tried to start it the second time later on, same thing again - the alarm light was dead and I couldn't disarm it. I disconnected the new battery again, let it sit for half an hour or so, and managed to get it going.

So I have ruled out the battery now and my multimeter is reporting 14V+ voltage at the battery terminals when the car is running, so it shouldn't be the alternator either.

Any ideas on how to troubleshoot this further? What else should I check?

Is it possible that a bad/old battery could have fried the alarm somehow when it was running out of current?

Also can anyone recommend a good auto elec in the inner or northern subs who knows Skylines well?

Thanks guys.

Edited January 12, 2014 by V28VX37

[Chris Rogers]

almoist sounds like a bad ground to me.

[V28VX37]

Thanks I'll check that out.

[V28VX37]

Ok so I did the following:

1. Bypass the immobiliser as per alarm's instructions
2. Reprogram the remote
3. Change remote battery
4. Check ground connections in engine bay

So far so good, the car starts and runs fine.

My best guess is that a dead main battery is the root cause. I reckon it also upset the alarm a bit as I think there's another battery in there somewhere that perhaps wasn't charging properly due to the main battery issue.

Anyhow, all good for now.

[V28VX37]

... aaaaand the issue is back, which sucks big time. I stalled in the turning lane couple of times today, not fun

It only seems to happen when idling and stationary. I think there may be multiple issues, here's a couple of further observations:

• There's a slight misfire on idle (has been for quite some time) and on one occasion a stall coincided with this. I ended up putting the car in Park at traffic lights and holding up the revs slightly (800 -> 1000rpm) and this got me home.
• More load on the engine increases the chances of a stall (power steering, headlights).
• When the car stalls it sometimes dies completely. No alarm led blinking, no hazard lights, AC and trip meters all reset. The alarm siren goes but very faintly?! It can usually be brought back after a while and a few attempts but obviously this is not safe in traffic.

I'm taking it back to the alarm shop for diagnostics but I'm not convinced that they'll be able to fix it all I feel that there may be something amiss with the immobiliser, and another semi-related electrical issue as well.

I'm terms of electronics, here's what's been added/changed over the years:

• Alarm/immobiliser
• ECU: Nistune board
• New coils (Yellow Jackets) and spark plugs
• Z32 AFM
• Fuel pump with rewire and relay
• Injectors

Oh yes - there's one other thing: When I bought the car it had the radio fuse removed. When it's back in, the (AM) radio works but the factory navigation system behaves erratically: the screen sometimes pops up by itself and shows a cryptic error message in Japanese. This car was obviously optioned with the JDM GPS from factory instead of the triple gauge cluster.

So it could almost anything ... Any suggestions on where to start & what to try? I'll probably end up taking the car an auto electrician in addition to the alarm shop, just want to see if there's any pointers I should give them.

Thanks!

[V28VX37]

I had the alarm shop have a look at it, they're not too sure either what it could be They disconnected the immobiliser circuit temporarily and it didn't stall since, although that is inconclusive and needs more testing.

One issue they picked up is that apparently the battery voltage is dropping whilst the car is running. This is obviously not right - could it be a faulty alternator afterall? Any other ideas?

I've got it booked with an auto electrician but they've got a week's queue so keen to try something else in the meantime if I can...

[Chris Rogers]

without having the car in front of me its hard to say.

low voltage would explain a few things though.

[V28VX37]

Cool thanks Chris. The theory is that low volts potentially cause the immobiliser to think that it's being disconnected, then cutting off the engine.

It's a prick of an issue though, hopefully the auto elec can find the root cause.

[V28VX37]

Late update just in case anyone's having similar problems...

Turns out the root cause here was a corroded connector right before the plus terminal of the battery. This means that the current sometimes got through and sometimes didn't. I still reckon this fluctuation caused the immobiliser to think that it's being disconnected, which cut off the engine at lower revs. I had the immobiliser disconnected for a while whilst it was being diagnosed and it never cut out during that time.

My auto elec removed the offending connector altogether (it was unnecessary anyway, no idea why it's been installed), we reconnected the immobiliser and the car has been running perfect ever since.

Anyway, moral of the story - check all the simple things first!!

[Chris Rogers]

Good to hear.

[V28VX37]

Thanks for your help on this Chris!