"Tamper" mode? Starts/stalls repeatedly, 10 minutes later it's fine

[Chevy-SS]

Anyone have experience diagnosing "tamper" mode issues with the VATS (vehicle anti-theft system)? I have a 98 Silverado which will run fine for about a month, then when I go to start it, it will run for a second, then die. It will do this until I just let it sit for about 10 minutes, then it will start and run fine for another month. It's driving me crazy.

I had a remote starter installed about a year ago and I suspected that might be part of the problem. I took it back to the installer, but he swears that the remote starter is completely bypassed when I use the key switch. He is saying that the problem lies somewhere in the VATS. It could be the resistor wire or the processor or the computer???

I notice my "security" light coming on every once in a while while I'm driving, so I am pretty sure my problems are in the VATS components somewhere. Anyone have any recommendations to help locate the problem?

[MadMac56]

Had that problem with my wife's malibu...pretty common problem...got worse & worse till BINGO out $400 for a new puter

[Chevy-SS]

MadMac, did you do the job yourself or did the dealer do it? If you did it yourself, was it difficult?

[MadMac56]

I shoulda...wasn't covered by the extended warranty...but the old lady handled it while I was at work...not sure how much was part & how much was labor...but I'd be willing to bet the part was at least half

[banshee350twincyl]

Im having the same problems as you but the only difference is that i dont have to wait 10 minutes, i try to crank it back right away and it cranks the 2nd or 3rd time, think it could still be the VATS. My trucks a 98 also .

[Jerry243]

I've got a 99 Silverado and had a very reputable business install a remote starter. Sometimes it works, sometimes it does not and when it does not, the security light flashes and I was told I need to put the key in the "ON" position for 10 minutes to bypass security issue, then start with key. I'm very dissapointed and am seriously looking at having the thing removed; fortunately, I have a lifetime warranty on parts and labor.

[Thunderbolt]

I have a buddy with the same problem and from what I have been told these trucks don't like after market remote starts. His causes the security system to activate. Does it do it even if you never use the remote starter ?? His seems to work if he never uses the remote starter, But if he tries to start it with the remote it dies and won't even start with the key for ten minutes. I don't know what brand his is, But he was standing outside talking to his neighbor one day and the neghbor sarted his car with his remote and at the same time it started my buddies truck !! Thats real promissing when someone elses remote starts your truck.

[Chevy-SS]

OK, my truck (98 Silverado) pissed me off today. It did the same "tamper mode" thing. I tried to use my remote start and it wouldn't start, I waited five or ten minutes, and then it started right up.

So today, I got ambitious and did the permanent bypass on the security wire. I found some instructions on the web. I cut the yellow wire, then measured the cranking ohms resistance at 577. Then off to Radio Shack, where they had 560 ohm resistors +/- 5%. I bought a pack of five for 99 cents. I measured the resistors to find the best one. Closest I could get (to 577) was 554 ohms, so I soldered that one onto the yellow wire (processer end) and into the orange/brown wire.

The instructions said I needed to be within 1% to 2% on the ohms. I was more like 4% off the 577, but the truck fired right up with no problem. I will be curious to see if the problem is now solved. I will post results after a week or two and let everyone know if this fix worked.

I'm no expert at this, but I've always suspected the remote start, especially as the resistor security wire goes through it via a relay. So now, I have completely eliminated the remote starter from the resistor security wire.

If this doesn't work, then I am gonna assume I need a new computer.

[ponchonutty]

Originally Posted by Chevy-SS

OK, my truck (98 Silverado) pissed me off today. It did the same "tamper mode" thing. I tried to use my remote start and it wouldn't start, I waited five or ten minutes, and then it started right up.

So today, I got ambitious and did the permanent bypass on the security wire. I found some instructions on the web. I cut the yellow wire, then measured the cranking ohms resistance at 577. Then off to Radio Shack, where they had 560 ohm resistors +/- 5%. I bought a pack of five for 99 cents. I measured the resistors to find the best one. Closest I could get (to 577) was 554 ohms, so I soldered that one onto the yellow wire (processer end) and into the orange/brown wire.

The instructions said I needed to be within 1% to 2% on the ohms. I was more like 4% off the 577, but the truck fired right up with no problem. I will be curious to see if the problem is now solved. I will post results after a week or two and let everyone know if this fix worked.

I'm no expert at this, but I've always suspected the remote start, especially as the resistor security wire goes through it via a relay. So now, I have completely eliminated the remote starter from the resistor security wire.

If this doesn't work, then I am gonna assume I need a new computer.

I can't say without looking at these vehicles but will tell you that GM has a high failure rate even without remote starts installed.

On the total bypass trick, I have found it better to be about 2% and have the resistance value a little higher versus being a little lower. For some reason when the temperature changes, you truck probably won't work because you are 4% AND lower than what it needs.

[Chevy-SS]

Ponchonutty, thanks for the feedback. Exactly what parts are you referring to when you say "high failure rate"? Computer? VATS processor? Security wiring harness?

So far, so good with this mod. The truck is working perfectly and the "security" light is staying off. I will take your advice though, and look around for a resistor that more closely matches the 577 ohms.

[ponchonutty]

Originally Posted by Chevy-SS

Ponchonutty, thanks for the feedback. Exactly what parts are you referring to when you say "high failure rate"? Computer? VATS processor? Security wiring harness?

So far, so good with this mod. The truck is working perfectly and the "security" light is staying off. I will take your advice though, and look around for a resistor that more closely matches the 577 ohms.

With the VATS systems it is usually the tiny little wires that go to the cyl. lock. They usually shortout from the cyl. being turned all the time to start the car.

With the Passkey systems, not really sure. All that I have ever seen GM do is COMPLETELY change the decoder ring and harness. When I have spoken to the techs, they didn't sound as if they really knew what the cause was either.

[Cadillakin'98]

So this is a common problem on all '98 full size (GM)trucks? Just wondering 'cause I haven't experienced this yet and hopefully won't but if I do it's nice to have this heads up on how to solve the problem

[Chevy-SS]

Originally Posted by ponchonutty

With the VATS systems it is usually the tiny little wires that go to the cyl. lock. They usually shortout from the cyl. being turned all the time to start the car.

With the Passkey systems, not really sure. All that I have ever seen GM do is COMPLETELY change the decoder ring and harness. When I have spoken to the techs, they didn't sound as if they really knew what the cause was either.

Well, if you are correct about the techs not knowing what the problem is, then shame on GM for producing this un-needed complexity.

I have now bypassed those tiny little wires that go to the cylinder lock, so hopefully the problem is solved. Still working perfectly. Plus, I went to see a buddy of mine who works with electronics and he built me a 576 ohm resistor using three in series. So I will install my new resistor which is almost exactly the measured cranking resistance.

I'll keep everyone posted, but right now it's looking like I got this problem beat.

Thanks

[ponchonutty]

Originally Posted by Cadillakin'98

So this is a common problem on all '98 full size (GM)trucks? Just wondering 'cause I haven't experienced this yet and hopefully won't but if I do it's nice to have this heads up on how to solve the problem

Well, you can't get a tech to actually admit it The ones that I talked to stated they never "dug into it" trying to find the fault. They just simply replaced the system.

It seems that the VATS system is the worse. I had it fail on my '89 Firebird. I average about 4 cars a year that I permenately bypass. As for the (Passkey)PK1,2,and 3 systems, I have yet to bypass one. I have had a few cars that would remote start but not with the keys. Later, the dealer ended replacing the system. I'm with you on this one. Got the PK2 system on my '01 Silverado and so far so good.

[Tall]

Where did you guys have your remote starts installed? They make an aftermarket Security By Pass for these vehicles. It runs about 60 bucks, depending on what alarm you have the price does differ. As far as I know, with the by pass…there is no issue.

What it does, is tricks the security system into thinking their is a key in the ignition...