1998 K2500 Passlock/VATS Question

[Xipher]

My truck is having annoying Passlock/VATS issues.

The security light turns on 2-5 minutes into every other drive and I'd say one out of every 10 starts it decides to give me the flashing security light of doom with a 2 second start and run before it dies.

I don't want to do the resistor mod, don't want to put another passlock sensor in or VATS box, I don't want to 'fix' it, I want to make a two prong attack on it that deletes it entirely by not depending on the VATS box even existing anymore or anything else and I need some help to do so.

First off, from what I can find, the VATS system just wants a 50hz signal sent to a pin on the PCM that tells it "everything is AOK" from the VATS module but for a 98, I /cannot/ find anyone who seems to know what pin this is, I can't even find a diagram that shows where the VATS module is in the truck or what the wires coming out of it are. If I knew the signal wire and location, I could just send the signal from there, anyone know? Does the 98' expect something other than the 50hz signal making this useless?

Also, and I know this sounds overkill, I've bought an HPTuners kit (being delivered tomorrow! Yes fixing this issue is worth the $450 for me) and I'm planning on disabling VATS on the PCM side of things. It's my understanding that doing this can still cause the security light to come on, but the security light signal I think is controlled by the VATS module sending a signal to illuminate it to the BCM? I don't want to see that light ever again for my entire life.

Between just saying 'screw it' and generating the signal the PCM wants to see /and/ telling the PCM to just ignore it I think I should be covering my bases to have this never be an issue ever again even if the PCM decides to look for the signal again after losing power or going nuts, etc?

I really.... REALLY /REALLY/ don't ever want to experience this /super fun time/ where the truck won't start because of VATS ever again since both times it's left me stranded it has been a *dangerous* (blocking an entire road the first time!) and exceptionally unpleasant situation.

Any pictures and diagrams would be much appreciated, thanks!

Anyways, I love this truck, I hate this problem, I will go nuclear scorched earth on VATS/Passlock.

 

[df2x4]

As far as I'm aware, if you disable PassLock in the tune you shouldn't ever see the light again while the truck is running. This is the first I'm hearing of a separate "VATS module." I was under the impression that GM's PassLock was completely contained in the PCM in these trucks.

 

[Deathpunch0311]

I had a buddy of mine tune out VATS/passlock with HP Tuners. That was 2 years ago. Haven’t had a problem since. The security light stays on but other than that. No problems.

 

[df2x4]

Interesting that the light stays on if there's an issue even if PassLock is disabled in the tune. If the original issue was with the sensor in the column then I bet you could get the light to go away by doing the resistor mod. Personally I'd be tempted to just pull the bulb in the cluster, though.

 

[east302]

Here is what I found on the Passlock for a 98, maybe it will help.

Someone scanned most of the factory service manuals here:

http://67-72chevytrucks.com/vboard/showthread.php?t=700011

The diagrams below are from alldatadiy.com which is about $30/yr per vehicle for a subscription. It’s pretty much the same as the manual, just a little easier to navigate.

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It says that you have to remove the ashtray to get to the EVO/Passlock module, so it must be kind of behind it. The diagram looks to be the view of the dash from the firewall side, looking into the cab.

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VCM connector pinout:

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Sent from my iPhone using Tapatalk

 

[df2x4]

I just found a similar description stating that the PassLock module is located below the slave CD pocket in the dash, which matches the diagrams @east302 just posted.

Also found this, the pinout at the bottom of the document may be another place that you can locate the PassLock data wire.

http://www.gmupfitter.com/files/media/photo/284/Bulletin_20.pdf

EDIT - If you read that whole document, it looks like you can disable the PassLock system (until battery power is disconnected completely) by simply breaking the connection on that one wire for more than five seconds while the truck is running. Doesn't look like it will help with the security light but it's interesting info.

 

[Deathpunch0311]

Interesting that the light stays on if there's an issue even if PassLock is disabled in the tune. If the original issue was with the sensor in the column then I bet you could get the light to go away by doing the resistor mod. Personally I'd be tempted to just pull the bulb in the cluster, though.

That’s exactly what I did lol

 

[Xipher]

There is so much good information in here I don't know where to start... I'll report back after work, but this is amazing!

It looks like what the 'EVO' wires are what I'm looking for, the pinout for the VATS box is interesting and it looks there's a likely wire (with a baud rate) that I should probe to see if its the signal...

If I'm looking at the software package right, I should be able to see if its a PWM (simple duty cycle 50hz signal) or a "serial" code on my PCM once I get HPTuners to dump it? If its the former it should be easy.

It also looks like the VATS box does in fact have a signal for the Security light, thats good to know, I'll have to see if its just a simple pull to ground or something?

I'd really like to get a definitive "this is how you defeat it at the source" going for people to look for and read once I get this sorted out... time permitting!

 

[Xipher]

Alright, I got HPTuners tonight, I read the PCM, I went to the VATS drop down box and went from "enabled" to "disabled", bought credits, wrote it back (FULL write, not just calibration!)

Did the open the doors, close the doors cycle with the truck off, turned the key, security light solid per usual..... and then the security light went out per usual (its an intermittent problem remember) and I started the truck, ran FINE, no security light at all.

I was confused at the light going out since every single person I've heard of doing this has the light on solid after doing so, so I turned the truck off, did a FULL read again and it showed VATS as "disabled" in the read back.

Since this is the 'first' step, I hope this actually worked? I'm really questioning if it did since the light isn't on solid like everyone says it should be...

I plan on cutting the yellow signal wire that provides the VATS box with the '5V-somerandomresistance' value to see if the truck will start after doing that as a test to see if its actually disabled...?

Just checking to see if my line of thought and such seems sane here, anyone else disable VATS on a 98 non-411 PCM and have their security light NOT stay on?

 

[df2x4]

From what I saw while Googling around yesterday it looks like the light should only stay on if there's a persistent issue with part of the PassLock system. If the rest of the system is functioning properly you shouldn't have the light on solid. If whatever your intermittent issue was flares back up you may get the solid light, but it shouldn't cause any issues. No experience personally as both of my trucks are '97s with no PassLock, but it sounds like you've got a good result so far.