95 VS Commodore Central Locking / Immobiliser Issues

[OZ38]

This issue with my VS Commy has been happening to me off & on for a few years now (3-4). Seem to happen around winter a lot & a heavy or long drizzling rain preceding the issue (Car is housed outside in the elements). But not every time is a wintery day, as it has also done it after a hot very humid night when there was a lot of moisture in the air.
The very first time this happened the doors would not unlock or lock via the remote key fob, as well the immobilizer would not disarm. I pulled every fuse & checked them, pulled all relays & swapped them around to see if one was sticking etc. Still Central Locking would not work off the remote fob, or the Immobiliser disarm. I gave up in disgust & consulted an Auto Spark who didn't really offer much advice. About a week later I tried the key fob & suddenly it's all working fine again.
Another time it did it again & I replaced all fuses, all relays. Still not disarming off the key fob. Went & got a new key fob & got it programmed. Still not working off the key fob remote. Turned the ignition on to reds for 45-50 mins & the red immobilizer light went out. Great able to start it. But as soon as I turned it off again, I had the same issue. Walked off again for about a week, then tried it. It opened the door locks & disarmed the immobilizer, started up fine, turned off & then restarted again without issues. Another 6months to a year goes by & it all happens again. Same as before, won't open the door locks & won't disarm the immobilizer. Left it for a couple of days & then it works again.
Another time it when it happened, there was a week or two between incidents. The second time I had to leave it for about 3 weeks, trying the key remote at various times until it suddenly starts to work again. Still nothing I do will work until it has had the rest time it seems to need. In the past I have lifted the bonnet & thrown the battery charger onto the cars battery terminals to keep it all topped up on charge. The new key fob & older key fob have been tried multiple times now.
As said earlier it seem to happen when the weather gets cold or damp, although I don't think it is a water in the electrics issue as the inside of the vehicle is very dry up under the dash above the BCM. I have replaced fuses, relays, key fobs etc, kept the cars battery fully charged. Still unable to get this car to be a reliable starter when I need it.
Do the BCM's have a battery that can die, or contacts inside that can be affected by change of weather or is there some other reason for this fault to be so intermittent ?
There is replacement / remanufactured / repaired low, mid & high-level spec BCM's available on evilbay from PEC for the VS V6 Commodores. Could replacing the BCM fix the issues ? They are a bit pricey at around $800, plus you have to send them your unit with Key fobs first. They then either fix yours (after testing & charging for testing) or send a remanufactured unit I believe.
Does anyone have ideas of other things or electrical connections I could check to solve this ongoing issue ?
After spending way more than I should have on this (cheap get to work) car, I find I can't rely on it in case it leaves me stranded after a rain shower while out or parked at work. Feeling I am almost ready to put a match to it

[antus]

It sounds like the whole BCM is dropping out. I would be looking for tarnished connections and open it up and check the PCB for visible damage.
But also for reliablity it's probably safest to turn of VATS in the PCM, so even if the BCM does fail you can open it and start it with the key without passing the security checks. Maybe use a club lock if you feel you need too, or a physical kill switch.

[VK_3800]

It doesn't really sound like this is the case here, but have you had issues with the heater blower speed or instrument lights? Sometimes when the electronic blower transistor dies it drives the BCM nuts

[OZ38]

It sounds like the whole BCM is dropping out. I would be looking for tarnished connections and open it up and check the PCB for visible damage.
But also for reliablity it's probably safest to turn of VATS in the PCM, so even if the BCM does fail you can open it and start it with the key without passing the security checks. Maybe use a club lock if you feel you need too, or a physical kill switch.

Thank you.
I will look to pull the BCM out & see if I find something obvious with connections. I myself am not good with Electronics but should be able to get someone in my area who is to look it over as well.

[OZ38]

It doesn't really sound like this is the case here, but have you had issues with the heater blower speed or instrument lights? Sometimes when the electronic blower transistor dies it drives the BCM nuts

The only issue sometimes is the Blower fan doesn't start from off position unless I slide the switch to max first & then back to 1,2 or 3 position.
Like it needs a kick start.
No problems with instrument lights at all.

[vlad01]

Could be a bad connector as others mentioned that is temp sensitive. Or a component in the BCM that has aged out of spec and/or has become temp sensitive.

On my VP, which run a dedicated immobilizer/receiver unit behind the middle of the dash (only accessible with dash out) has become temp sensitive, but inverse to your symptoms. My range shrinks to sometimes only 30cm from the car when hot, and can return to a more usable 10m in the cold, and each run of the remote the distance fluctuates. I have a brand new remote, but this behavior still persists. I replaced the ATM in the dash with another matching remote, it made no to little difference. So I think all of the units are aging and the receivers aren't working anywhere near as well anymore.

Inside the VP ATM, there is quite a lot of electrolytic caps and other film caps that all can age and become temp sensitive.

I do believe this is the frequency band drifting in and out of range of the remote transmitter, as the VP factory remotes have a tunable transmitter via a fine adjustment trim cap, and I have often in the past used them to get the remotes to work again or gain their distance via re-tuning them, but I now use a universal programmable remote, and so the frequency is handled digitally via the IC they use in them, so the frequency is stable and unchanging from initial cloning, so that points to the receiver in the car drifting frequency with temp changes.

So one could feasibly remove a BCM or in my case the ATM, recap it and replace/repair any other faults or dodgy components and it should work like new again.

In the VP ATM, there is also a trim cap there too. So its a matter of tuning both the frequency to the antennas in the ATM as you would in the remote. I assume the BCM doesn't have this adjustability as the remote key fobs didn't have this as far as I recall, probably as the later model electronics was designed better to not need fine tuning from the factory, but if anything, the older VP ones allowed me to narrow down and ruling out tuning issues as a factor, leaving aged components as the likely cause.