Please help with my engine light codes

[Danielgreig]

First off, I know it can be difficult to diagnose the issue online with just the codes. However I’m hoping to get some feedback on what to check. Now for the issue:

So my Tahoe was sitting for about a month due to a bad back injury I had. I finally got a chance to go and start it and it needed a jump. A buddy came by and jumped it for me and the engine light came on. I plugged in my scanner today and it shows the following codes. P0740, P0785, and P2761. All have to do with the transmission. Has anyone else had an issue like this? Does anyone know what I should check before taking it to a shop. I would rather fix myself if possible. Below are the pictures of the scanner. Any help is appreciated.

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[LionsGuy]

How does it ride? Have you driven it? Check the trans fluid? Any Leaks?

 

[Danielgreig]

How does it ride? Have you driven it? Check the trans fluid? Any Leaks?

I did drive it after the jump and it drove just fine but Only around my neighborhood. Got it to maybe 35mph tops and drove it for about 20 minutes. I haven’t yet check the transmission fluid. I will do that next once I get home.


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[Matthew Jeschke]

With all those open circuit faults i feel as though you lost a connection in your harness. Possible all those items are in one wire bundle?

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[Fless]

I'd be taking a good look under the body to see if there is any rodent or other damage to wiring, especially near the tranny.

 

[Danielgreig]

With all those open circuit faults i feel as though you lost a connection in your harness. Possible all those items are in one wire bundle?

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I was also wondering if it could be something electrical due to the dead battery and then the jump start. I’m hoping it’s not a fried ecu or whatever controls the transmission. I’m not sure how I would check that.


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[Danielgreig]

I'd be taking a good look under the body to see if there is any rodent or other damage to wiring, especially near the tranny.

I’ll take a look at that as well.


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[Matthew Jeschke]

I was also wondering if it could be something electrical due to the dead battery and then the jump start. I’m hoping it’s not a fried ecu or whatever controls the transmission. I’m not sure how I would check that.


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I dont think would be a fried ecu. Likely just a bad connection. There is a harness going to transmission... or possible a bad ground.

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[Danielgreig]

I dont think would be a fried ecu. Likely just a bad connection. There is a harness going to transmission... or possible a bad ground.

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Interesting....possibly a bad ground going to the transmission? Is there a ground wire just for the transmission?


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[Danielgreig]

Thanks guys for all the replies so quickly with ideas for me to check into. I really appreciate it.


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[iamdub]

Definitely check the harnesses if there's a chance of a mouse or squirrel chewing anything. Other than that, I wouldn't be too terribly concerned given the circumstances. Loss of power/low power can easily make any of the ECUs on these things go haywire. If it drove fine, then those three systems are probably operating fine. Drive it easily for a few miles to get all the fluids, etc. warmed up then take it on the highway to reach a cruising speed. While holding the throttle pedal steady (not with cruise control), lightly touch the brake just enough to activate the brake lights then release. The tach should jump up a few hundred RPM for a few seconds then go back down. This will test the operation of the Torque Converter Clutch (TCC). If this and all other functions seem fine, those were probably one-time fault codes due to the power loss and they will clear themselves over a few drive cycles. I wouldn't clear them so I could see them go away on their own.

 

[SnowDrifter]

In addition to what's been posted: Disconnect your battery, stomp on the brakes, go get a drink of water and hook it back up

I've had some really weird shit happen when I've run a battery down. Dead is fine. But if it's borderline dead, a lot of the electrical bits seem to get fussy until they're properly reset.

Did you have these codes prior to the dead battery? Not saying this is a fix. More of a first pass before proceeding

 

[Doubeleive]

I agree with these guys, if it sat for a period of time maybe some moisture in the harness caused a poor electrical connection, my sister in Oregon unfortunately had rats chew up all kinds of stuff on her Chrysler she drove it with an assortment of codes until the motor finally seized up, it wasn't worth the cost to try and fix all the stuff they had chewed up, freaking critters like to get inside where it's warm and then try to make a nest.

 

[Danielgreig]

Definitely check the harnesses if there's a chance of a mouse or squirrel chewing anything. Other than that, I wouldn't be too terribly concerned given the circumstances. Loss of power/low power can easily make any of the ECUs on these things go haywire. If it drove fine, then those three systems are probably operating fine. Drive it easily for a few miles to get all the fluids, etc. warmed up then take it on the highway to reach a cruising speed. While holding the throttle pedal steady (not with cruise control), lightly touch the brake just enough to activate the brake lights then release. The tach should jump up a few hundred RPM for a few seconds then go back down. This will test the operation of the Torque Converter Clutch (TCC). If this and all other functions seem fine, those were probably one-time fault codes due to the power loss and they will clear themselves over a few drive cycles. I wouldn't clear them so I could see them go away on their own.

That’s really good advice. Thank you. It’s a bit rough being away from home now and worrying about it. I’ll dive into it as soon as I get home.


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[Danielgreig]

In addition to what's been posted: Disconnect your battery, stomp on the brakes, go get a drink of water and hook it back up

I've had some really weird shit happen when I've run a battery down. Dead is fine. But if it's borderline dead, a lot of the electrical bits seem to get fussy until they're properly reset.

Did you have these codes prior to the dead battery? Not saying this is a fix. More of a first pass before proceeding

Also a great idea. I’m liking all the fairly easy things to check first.


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[Danielgreig]

I agree with these guys, if it sat for a period of time maybe some moisture in the harness caused a poor electrical connection, my sister in Oregon unfortunately had rats chew up all kinds of stuff on her Chrysler she drove it with an assortment of codes until the motor finally seized up, it wasn't worth the cost to try and fix all the stuff they had chewed up, freaking critters like to get inside where it's warm and then try to make a nest.

I do live in Eugene Oregon and this area has had a bad rat problem recently. I sure hope this isn’t the issue. Chasing down an electrical problem like this sounds like a nightmare.


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[Danielgreig]

Also, to answer the question above, no the codes were not there until after the battery died and I had to get it jumpstarted.


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