Theft Light flashes - no start

[Aplieesi]

Hello guys!

I'm having issues with my 97 Expy 5.4L. About 3 months ago I started to get in the vehicle and the theft light would prevent me from starting it. I would take the key out and re-insert it and theft light would go out and it would start right up. Within a week it seemed to have died on me completely. I took the leads off the battery and put them together to try to drain all electricity form capacitors and that did the trick. Since then I added aftermarket key (since I only had one) and it programmed by a auto lock specialist just fine. Yesterday I drove it one mile to the store and when I went to get back into it, it did not start. Theft light flashes just like before...

What could I test and how could I test it? I was thinking about getting the PATS transponder behind the steering wheel form pick n pull to swap it. What are your thoughts?

Brief History:

PCM replaced about a year ago with a used one due to rain damage from leaky windshield. Got windshield fixed and I'm pretty sure the used PCM I installed had water damage on it as well (rust was on the back of it... After I replaced it, truck started up just fine though.

 

[Aplieesi]

Well here's an update. It's been just over 24 hours since I once again disconnected the battery and connected both posts to drain power from all systems. Tried to start it and nothing. Called AAA to get it towed and sure enough as the tow truck driver asks for the key...he gets in it and starts it right up! Doesn't make any sense to me? Anyone out there experienced this before? I'd like to figure out if there is any tests I can make on relays or on the PATS components... Help

 

[rjdelp7]

First do not ever cross battery terminals. Disconnect negative terminal and hit the horn or turn on headlights. That will drain any stored voltage. This is also not recommended , because your PCM, will have to do a hard re-boot/re-learn and transmission shifting and idle may go nuts. Second, try a different PATS key or flip key around in ignition. Third, do not hit, driver side door lock switch, with key in ignition and door open. This will activate theft system. Always lock it, with the fob.

 

[Aplieesi]

First do not ever cross battery terminals. Disconnect negative terminal and hit the horn or turn on headlights. That will drain any stored voltage. This is also not recommended , because your PCM, will have to do a hard re-boot/re-learn and transmission shifting and idle may go nuts. Second, try a different PATS key or flip key around in ignition. Third, do not hit, driver side door lock switch, with key in ignition and door open. The will activate theft system. Always lock it, with the fob.

Thank you for your insights. I'll keep them in mind. I did try both keys I have, flipped them several times. Seems like the PATS system works when it's ready to work.

If I find a used PATS transponder that goes on the steering column and replace mine, do you think I would need to re-code the keys?

 

[rjdelp7]

Thank you for your insights. I'll keep them in mind. I did try both keys I have, flipped them several times. Seems like the PATS system works when it's ready to work.

If I find a used PATS transponder that goes on the steering column and replace mine, do you think I would need to re-code the keys?

Does your vehicle have or ever had a remote start? Hack installers zip tie a PATS key inside column, to fool anti theft.

 

[Aplieesi]

Does your vehicle have or ever had a remote start? Hack installers zip tie a PATS key inside column, to fool anti theft.

No it hasn't. This vehicle has been in our family for 20 years. I took the steering column apart to see if I could visualize any defects, bad connectors... and consequently noticed that everything seemed normal.

 

[rjdelp7]

I doubt you have a bad transponder. Mine did same thing, when I locked doors with power lock switch, with key in ignition.

 

[Aplieesi]

I doubt you have a bad transponder. Mine did same thing, when I locked doors with power lock switch, with key in ignition.

ok, I don't think I did that. But if I or my wife did that by accident...how do you fix the issue?

 

[rjdelp7]

ok, I don't think I did that. But if I or my wife did that by accident...how do you fix the issue?

Do not leave keys in ignition. Always lock with fob, after exiting vehicle and all doors closed.

 

[don b]

has it been raining or even maybe a high dew point ? Mine's a 99, had a hard rain, got lucky because I drove to walmart, shopped, came home. Car didn't start again for a couple of days - I didn't know anything about the GEM / windshield problem and thought the security system kicked in for some reason because the security light was flashing like crazy.
If by chance u don't know anything about the GEM issue there's a ton of info on it. If all else seems fine, I wouldn't rule that out