my brother has an 02 envoy I6 and every once in a while he will go to start it and it wont let him but if you wait 10-20 mins it will start. this is getting really annoying now because its becoming more frequent. he said he asked someone and they said it was some sort of security lock (makes sense cause the security light flashes). we took it to the mechanics to get the codes read but it will only come up when the issue happens. when it finally did happen it came up as either a U1000 pr P1000 (cant remember exactly)the mechanic said it was a computer module that was the cause but the reader didnt say which one. he said he would have to go through all the modules to find the culprit. now heres my issue. if its a security problem why wouldnt you just check the security module first? checking all of them seems like a waste of his time and our money. have any of you had a problem like this? if so please tell me how you fixed it
random starting issue
- Thread starter fishin757
- Start date
I would guess the ignition switch is on it's way out. They have a reputation for causing all kinds of weird electrical issues. It's a less than $40 part from your local auto parts store, and probably take you a half an hour to change out. 
The "security" function is part of the PCM, and there could be a fault in the Passlock system in the steering column. But it's more likely to be the ignition switch.
When it fails, does it do nothing, or do some lights and gauges come on and the starter fails to turn over? Or do you hear a click in the front fuse block that could indicate the starter relay is being activated but the starter doesn't spin?
Lots of ways for the vehicle to fail to start, and the troubleshooting tree begins with taking detailed observations about exactly how it behaves when it's misbehaving.
When it fails, does it do nothing, or do some lights and gauges come on and the starter fails to turn over? Or do you hear a click in the front fuse block that could indicate the starter relay is being activated but the starter doesn't spin?
Lots of ways for the vehicle to fail to start, and the troubleshooting tree begins with taking detailed observations about exactly how it behaves when it's misbehaving.
I think you're thinking your Avalanche, Ray. We have no Passkey system, only a Passlock, there the security resistor chip is built into the vehicle's cylinder, not the key itself. If our key turns the cylinder, it can't be the key. I have to assume if the OP had a key that wouldn't turn he would have suspected the cylinder mechanics.RayVoy said:
, I did forget the 360 trucks use the passlock system. :banghead:It's not the key because we have used the spare with the same results. When the key is in the position just before actually cranking it all the dash lights are on like normal and gauges do their thing. When you go to turn it over all le lights go off like they normally would except the security one. The starter makes no noises an there is no click in the colomn. I want to say he has had the ignition changed before but I'm not positive
ElAviator72
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- Jan 11, 2012
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- 118
Sounds suspiciously like our last ignition switch failure. Same symptoms 
Eventually, the igniton switch will cut in and out while you are driving, and the PCM throws a code at that point.
Eventually, the igniton switch will cut in and out while you are driving, and the PCM throws a code at that point.
At least ignition switches are cheap, like $30. IIRC. Last time I saw one on Ebay for $5 I snagged it for a second spare.
The electrical part of the ignition switch for us is separate from the key cylinder where the keying is done. Cheaper and much easier to replace. And they have a horrible failure rate.