My 2004 Yukon started itself when I connected the battery cables, no key in ignition.

[Hugh937]

Has this happened before, or do I have a scary problem. On my 2004 Yukon Denali, my battery went stone cold dead (0 voltage), and I picked up a replacement battery. I connected the positive terminal, and then the negative terminal, and the vehicle started and ran by itself. There was NO key in the ignition, and I don't even have key fobs for it. Putting the key in the ignition did nothing. Disconnecting the negative terminal did nothing, I could not kill the engine till I pulled the fuel pump fuse. Needless to say I was more than a little concerned as if something or a body part had been in the belts, etc., it could have been catastrophic. I replaced the fuse, and repeated connecting the negative terminal, and it did it again, no key in the ignition, and no key control of the car. The third time the car did not start, and placing the key in the ignition did allow the engine to be turned on and off properly. Do I have some sort of problem with an ECU in the engine. I don't want to put my hands around the engine without pulling the relays for the ECM's, and I am not sure on all to pull. I am going to be scared to work on the vehicle without these procedures, killing the fuel pump would still allow the engine to run for a short period. Is this normal, or something that could happen because of the zero voltage on the system? Or do I have a weird electrical problem on it that should not be there. Needless to say, the other functions the ECU runs such as the air bags scare me if I worked around the dash because of this spontaneous problem. Anyone with any insights?

 

[Doubeleive]

Has this happened before, or do I have a scary problem. On my 2004 Yukon Denali, my battery went stone cold dead (0 voltage), and I picked up a replacement battery. I connected the positive terminal, and then the negative terminal, and the vehicle started and ran by itself. There was NO key in the ignition, and I don't even have key fobs for it. Putting the key in the ignition did nothing. Disconnecting the negative terminal did nothing, I could not kill the engine till I pulled the fuel pump fuse. Needless to say I was more than a little concerned as if something or a body part had been in the belts, etc., it could have been catastrophic. I replaced the fuse, and repeated connecting the negative terminal, and it did it again, no key in the ignition, and no key control of the car. The third time the car did not start, and placing the key in the ignition did allow the engine to be turned on and off properly. Do I have some sort of problem with an ECU in the engine. I don't want to put my hands around the engine without pulling the relays for the ECM's, and I am not sure on all to pull. I am going to be scared to work on the vehicle without these procedures, killing the fuel pump would still allow the engine to run for a short period. Is this normal, or something that could happen because of the zero voltage on the system? Or do I have a weird electrical problem on it that should not be there. Needless to say, the other functions the ECU runs such as the air bags scare me if I worked around the dash because of this spontaneous problem. Anyone with any insights?

that is some strange behavior
some additional information is usually helpfull
such as:
are you the original owner?
if not how long have you owned it?
what is the mileage?
any 3rd party equipment installed? i.e. aftermarket alarm, anything connected to the obd, etc
is it a rust state vehicle? how is the rust?
any work done to it recently other than a dead battery?
any questionable or non-factory looking wiring anywhere?

 

[strutaeng]

Try swapping the starter relay. I had a relay get stuck ON once and it was weird as heck. I can't remember which one it was, headlights maybe? I simple swap revealed it was the relay.

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

That issue is surely an odd one, but you are already receiving sage advice from the knowledgeable folks on this Forum.

 

[Hugh937]

that is some strange behavior
some additional information is usually helpfull
such as:
are you the original owner?
if not how long have you owned it?
what is the mileage?
any 3rd party equipment installed? i.e. aftermarket alarm, anything connected to the obd, etc
is it a rust state vehicle? how is the rust?
any work done to it recently other than a dead battery?
any questionable or non-factory looking wiring anywhere?

Hi:
As to your questions, lets see if I can answer them all. I am not the original owner, I bought it at 105K miles and it has approximately 125K miles after 4 years (I don't go very far to work, etc.). After looking around, and with the little routine thiings I did with it, everything is original. The only repair made so far was at a shop, to replace the actuator that controlled the central AC vent (I had the blow hot and cold problem that is common with the AC systems on these vehicles.) That was over two years ago, and no problems except oil and air filter, etc. changes since then. I did replace the battery as it was 7 years old about 1 1/2 years ago. As far as I can tell the car is completely original, there are no mods, add ons, rewire jobs, it all looks original everywhere. It has never given me any trouble except for the AC problem. I live iin Florida, and the car came from Alabama, and has no rust or decay anywhere on it. I have no idea why the 1 1/2 year old battery drained completely in 8 days. It was at 0.0 volts, attempting to charge it resulted in 2.3 volts, so I was pretty sure it was no good, as did the Autoparts store I bought it at. Why it drained to 0, I have no idea. It never did that before. I checked when I put the new battery in with an ammeter if it was drawing any current parked, and the amperage was something like .002 amps or something like that. .001 amps times 24 hours times 10 days is .24 amp hours, which is essentially nothing. All I can guess at is that the ECU did not like having the power completely off, and something needed to be "relearned." But it did it twice before it has and does work normally. But it still scares me since working around the engine without pulling the engine ECU relay and the fuel pump needs to be done everytime somebody needs to work around the engine compartment. Let alone what other scenarios you could imagine. Should I call a GM dealer and ask to speak to a mechanic? Where would I go to find out if this problem exists somewhere else. I could not find anything on the net, but need to search some more. Thanks for the response.

 

[blackelky]

Hi:
As to your questions, lets see if I can answer them all. I am not the original owner, I bought it at 105K miles and it has approximately 125K miles after 4 years (I don't go very far to work, etc.). After looking around, and with the little routine thiings I did with it, everything is original. The only repair made so far was at a shop, to replace the actuator that controlled the central AC vent (I had the blow hot and cold problem that is common with the AC systems on these vehicles.) That was over two years ago, and no problems except oil and air filter, etc. changes since then. I did replace the battery as it was 7 years old about 1 1/2 years ago. As far as I can tell the car is completely original, there are no mods, add ons, rewire jobs, it all looks original everywhere. It has never given me any trouble except for the AC problem. I live iin Florida, and the car came from Alabama, and has no rust or decay anywhere on it. I have no idea why the 1 1/2 year old battery drained completely in 8 days. It was at 0.0 volts, attempting to charge it resulted in 2.3 volts, so I was pretty sure it was no good, as did the Autoparts store I bought it at. Why it drained to 0, I have no idea. It never did that before. I checked when I put the new battery in with an ammeter if it was drawing any current parked, and the amperage was something like .002 amps or something like that. .001 amps times 24 hours times 10 days is .24 amp hours, which is essentially nothing. All I can guess at is that the ECU did not like having the power completely off, and something needed to be "relearned." But it did it twice before it has and does work normally. But it still scares me since working around the engine without pulling the engine ECU relay and the fuel pump needs to be done everytime somebody needs to work around the engine compartment. Let alone what other scenarios you could imagine. Should I call a GM dealer and ask to speak to a mechanic? Where would I go to find out if this problem exists somewhere else. I could not find anything on the net, but need to search some more. Thanks for the response.

Those models had funky ignition switch tumblers too if you or the previous owner had a lot if weight on your key ring set

 

[rockola1971]

This is a cool one. Alot of things have to happen in order for the starter to crank and engine actually start (ignition and fuel). And all of those come together at the ignition switch (not to be confused with the ignition lock cylinder). The ignition switch likely has burn/welded contacts. Its fairly easy to change out and doesnt cost much either. Just have to do a relearn for the factory security system.

 

[Doubeleive]

Hi:
As to your questions, lets see if I can answer them all. I am not the original owner, I bought it at 105K miles and it has approximately 125K miles after 4 years (I don't go very far to work, etc.). After looking around, and with the little routine thiings I did with it, everything is original. The only repair made so far was at a shop, to replace the actuator that controlled the central AC vent (I had the blow hot and cold problem that is common with the AC systems on these vehicles.) That was over two years ago, and no problems except oil and air filter, etc. changes since then. I did replace the battery as it was 7 years old about 1 1/2 years ago. As far as I can tell the car is completely original, there are no mods, add ons, rewire jobs, it all looks original everywhere. It has never given me any trouble except for the AC problem. I live iin Florida, and the car came from Alabama, and has no rust or decay anywhere on it. I have no idea why the 1 1/2 year old battery drained completely in 8 days. It was at 0.0 volts, attempting to charge it resulted in 2.3 volts, so I was pretty sure it was no good, as did the Autoparts store I bought it at. Why it drained to 0, I have no idea. It never did that before. I checked when I put the new battery in with an ammeter if it was drawing any current parked, and the amperage was something like .002 amps or something like that. .001 amps times 24 hours times 10 days is .24 amp hours, which is essentially nothing. All I can guess at is that the ECU did not like having the power completely off, and something needed to be "relearned." But it did it twice before it has and does work normally. But it still scares me since working around the engine without pulling the engine ECU relay and the fuel pump needs to be done everytime somebody needs to work around the engine compartment. Let alone what other scenarios you could imagine. Should I call a GM dealer and ask to speak to a mechanic? Where would I go to find out if this problem exists somewhere else. I could not find anything on the net, but need to search some more. Thanks for the response.

I agree with these other guys it is most likely the ignition switch
it's probably the cheapest easiest thing to try at any rate.
I would get a oem one from the dealer if they are still available, you can get it at the parts department and ask them to re-key it to your key.
some aftermart ones are not able to be rekeyed
plenty of youtube video's on how to, you just remove the shround around the ignition, turn the key forward inset a pin a hole and pull it out, insert the new one.
then you can do either a 10 minute releaern or 3X10 min relearn, then it should start, once you have it relearned, try disconnecting the battery and reconnect see if the problem is gone.

 

[Sparksalot]

Christine!

 

[rockola1971]

Try swapping the starter relay. I had a relay get stuck ON once and it was weird as heck. I can't remember which one it was, headlights maybe? I simple swap revealed it was the relay.

I can see the starter relay welded shut cause the engine to CRANK with no key in the ignition but you wouldnt get fuel pump relay enable and ignition system enable from just that which would keep you from getting an actual engine START.