Need a little help!!

[Speedslow]

ok so 2004 Tahoe 5.3 runs perfect no cel but when I hook into diagnostics plug with scanner it will lose connection for a split second when I crank it This is a problem because for inspection it needs to have all monitors open but every time it’s shut off it loses connection and has to start all over again. Tried searching with no luck. Tested all connections at pcm for power and ground and everything is good no chewed wires or blown fuses. I’m stuck and need to get this inspected. Any help would be greatly appreciated

 

[OR VietVet]

Did you check all wiring at the starter?

 

[ks03]

Weak battery or poor connection at battery could cause the voltage to dip too much when cranking

is your scanner having issues or a shop when doing the inspection? If a shop is hooking up with something not powered by your car, it could be a non issue if you are having trouble.

 

[Speedslow]

Weak battery or poor connection at battery could cause the voltage to dip too much when cranking

is your scanner having issues or a shop when doing the inspection? If a shop is hooking up with something not powered by your car, it could be a non issue if you are having trouble.

Battery is 2 months old. I will double check all connections again and also look at starter wiring. Thanks for the suggestions I will let you know

 

[Doubeleive]

most likely it's your scanner loosing power, does it run off of the vehicle 12v or does it have it's own battery/power supply?

 

[Rocket Man]

My Tech2 does the same thing, it will reset if I hit the starter unless I use the external power supply. I’m pretty sure your OBD port loses power for a split second as part of the normal operation when the starter hits. You need an external source of power for it to not happen. Not sure if all the accessory outlets lose power at that time or not.

 

[Speedslow]

most likely it's your scanner loosing power, does it run off of the vehicle 12v or does it have it's own battery/power supply?

Tried 3 different scanners all do the same including the inspection station. It links to all scanners but when you go to start it the connection cuts off for a split second and starts to re connect. And it clears the monitors every key cycle. I will recheck everything tomorrow. It’s driving me crazy because it runs perfect and everything else works as it should

 

[Doubeleive]

Tried 3 different scanners all do the same including the inspection station. It links to all scanners but when you go to start it the connection cuts off for a split second and starts to re connect. And it clears the monitors every key cycle. I will recheck everything tomorrow. It’s driving me crazy because it runs perfect and everything else works as it should

doesn't answer the question but I would assume the inspection station runs on it's own ac power, you might check or replace the cigarette lighter fuse for the drivers side that is what supplies 12v power to the obd port and check the bcm connectors to be sure they are all in snug and tight, same for the ecm under the hood. maybe even try connecting a battery charger to it while you are at home and while testing to see if that makes any difference.

 

[Doubeleive]

the only thing that would make any sense otherwise is if you had a short somewhere, it's normal for the voltage to drop to about 5v when starting which causes some scanners to loose power and restart but the bcm should still run off of that 5v or so unless it's shorting out. that's the only thing I can think of

 

[Speedslow]

The obd2 port has power but the actual pcm keeps resetting when cranked

 

[Rocket Man]

If your monitors are resetting you will have to do a lot of drive cycles after you fix the problem. I forget which one takes forever.

 

[Speedslow]

If your monitors are resetting you will have to do a lot of drive cycles after you fix the problem. I forget which one takes forever.

BUT it does it every time I shut it off. So even if I drive until they are all ready and take it to the ny inspection it requires them to have key on engine off so then it clears the monitors and it won’t pass. It’s very strange. Inspection guy told me every time he has seen one do that it was mice in the engine fuseblock but checked and mine is super clean also checked pcm removed cover no chewed wires and checked all pcm power and grounds and everything is good.

 

[Doubeleive]

BUT it does it every time I shut it off. So even if I drive until they are all ready and take it to the ny inspection it requires them to have key on engine off so then it clears the monitors and it won’t pass. It’s very strange. Inspection guy told me every time he has seen one do that it was mice in the engine fuseblock but checked and mine is super clean also checked pcm removed cover no chewed wires and checked all pcm power and grounds and everything is good.

sounds like you might have to yank one from a junker then and have it reprogrammed unless you have a tech2 then you can do it via a pc/laptop for $40

 

[Rocket Man]

BUT it does it every time I shut it off. So even if I drive until they are all ready and take it to the ny inspection it requires them to have key on engine off so then it clears the monitors and it won’t pass. It’s very strange. Inspection guy told me every time he has seen one do that it was mice in the engine fuseblock but checked and mine is super clean also checked pcm removed cover no chewed wires and checked all pcm power and grounds and everything is good.

Yessir, that’s why I said AFTER you fix the problem that’s causing them to reset. Sorry about your situation, that sucks.

 

[PG01]

BUT it does it every time I shut it off. So even if I drive until they are all ready and take it to the ny inspection it requires them to have key on engine off so then it clears the monitors and it won’t pass. It’s very strange. Inspection guy told me every time he has seen one do that it was mice in the engine fuseblock but checked and mine is super clean also checked pcm removed cover no chewed wires and checked all pcm power and grounds and everything is good.

Im in NY, i feel your pain.

Heres an option and what i do for my fil’s junker...set and an inspection appt for a time that your guy can work with you and you alone...Drive it to reset your monitors
(evap takes forever @Rocket Man ) then with out shutting it off let them hook it to insp mach....Just leave it running. All my guy does evey time, with all my cars.. always drive right in and hook it up i never have to have eoko you are allowed (in ny) to have 1 ‘not ready’ monitor and/or 1 pending check engine.... as long as all the others are ready, 1 unready is ok for a pass.

all that said, it sounds like you have a ground problem, as in the pcm sees a battery disconnect and is clearing your monitors.... check all grounds , especially the neg battery cable.

If there is any issues, with any monitors, you’ll never have a check engine light until the monitors go through a complete cycle but you wont know because every time you shut it off they clear, like a battery disconn.

hope that makes sense

 

[bladenbullet]

Disable your fuel pump and voltage drop your battery cables while cranking...both positive and negative...you have an intermittent connection somewhere and that's the place to start...also measure voltage at the battery during cranking to be sure it isn't dropping below an acceptable level ro keep the PM alive...

 

[Speedslow]

Disable your fuel pump and voltage drop your battery cables while cranking...both positive and negative...you have an intermittent connection somewhere and that's the place to start...also measure voltage at the battery during cranking to be sure it isn't dropping below an acceptable level ro keep the PM alive...

Did multiple tests and everything seems fine. Thinking it’s the pcm but I will definitely do a voltage drop test today after work. Thanks will let you guys know the results

 

[Speedslow]

So I just found a kid willing to leave it running and got it inspected. He also believes it’s a pcm problem. I am still going to test it to make sure later. Thanks everyone for the help!!