Originally posted by Eric
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1999 Tahoe Stalling Issue
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Originally posted by Eds_Automotive View Post
Yea, its an aftermarket tune on an updated style PCM, LS1 mapping possibly. The engine is out of a 1998 motohome, and its fuel injected. Im going to check voltage to the transmission as soon as I can. I doubt its a limp mode but I keep getting suggestions that the torque converter is trying to lock up in 1st but I dont see any evidence that suggests it will completely cut the ignition off if that happens.
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Originally posted by Eric View Post
A locked up converter, is like stopping vehicle without pushing on the clutch, it'll stall it.
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This is why they take it to expert mechanics lol.
When I rewired this 2003 Trailblazer, there were three yellow wires and three pink wires going from the plug in the trans up to the computers. took forever to find diagrams, since there are three plugs in the 2003 and colors changed year to year. It just started so has to be something breaking down or loading up because it has been wrong for a while.
Is it even possible to get a stand alone TCM for that trans?
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Originally posted by anotheridiot View PostThis is why they take it to expert mechanics lol.
When I rewired this 2003 Trailblazer, there were three yellow wires and three pink wires going from the plug in the trans up to the computers. took forever to find diagrams, since there are three plugs in the 2003 and colors changed year to year. It just started so has to be something breaking down or loading up because it has been wrong for a while.
Is it even possible to get a stand alone TCM for that trans?
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Originally posted by Eds_Automotive View Post
Ive never heard of that many problems on a 4L60, I know they went through some changes but wiring should be pretty consistent. However, I dont have a 4L60 in this truck, its a 4L80 from a motorhome, standalone trans controlelr wont help since there is no issue controlling the transmission. Those controllers are for people doing custom builds where they put modern parts in old school vehicles.
First post states a range switch problem, part of the 7 wire circuit going back there.
Second post said he was having trouble with engaging over drive.
Sounded like they thought it was trying to lock up the converter in first or second from one of the posts.
When I finally found the diagrams on the 2003, there are three plugs that go to the ECU mounted on the side of the plastic intake plenum. I had to follow those pins all the way down to the harness. The harness I got was from a 2006, so the plugs were different and needed to splice the old one in so I could hook up the trans. I chose to just buy a new neutral safety switch from the 2006 so I did not have to go thru all those wires. Everything worked except for the range indicator on the dash. I chased every wire and found a ground that went to an empty pin terminal. I cut that ground wire out of the harness and attached it to the engine for ground and the range indicator showed up. The rest were listed as a high or low resistance limits for the computer.
It seems like alot of work for a little dash of light, but we have a 2003 1 ton van that chews up neutral safety switches and spits them out. The range indicator just stays in r, d or somewhere when its in park and the car wont start. So I feel its a little important.
So I would see if you could fit the original range switch on that trans and that might go away since all the wires are in the right place on the pins. But that other connector, I would chase down. Maybe you can just start with every ground wire and find one that is not connected at the computer.
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Originally posted by anotheridiot View Post
It sounds like you have issues with the transmission.
First post states a range switch problem, part of the 7 wire circuit going back there.
Second post said he was having trouble with engaging over drive.
Sounded like they thought it was trying to lock up the converter in first or second from one of the posts.
When I finally found the diagrams on the 2003, there are three plugs that go to the ECU mounted on the side of the plastic intake plenum. I had to follow those pins all the way down to the harness. The harness I got was from a 2006, so the plugs were different and needed to splice the old one in so I could hook up the trans. I chose to just buy a new neutral safety switch from the 2006 so I did not have to go thru all those wires. Everything worked except for the range indicator on the dash. I chased every wire and found a ground that went to an empty pin terminal. I cut that ground wire out of the harness and attached it to the engine for ground and the range indicator showed up. The rest were listed as a high or low resistance limits for the computer.
It seems like alot of work for a little dash of light, but we have a 2003 1 ton van that chews up neutral safety switches and spits them out. The range indicator just stays in r, d or somewhere when its in park and the car wont start. So I feel its a little important.
So I would see if you could fit the original range switch on that trans and that might go away since all the wires are in the right place on the pins. But that other connector, I would chase down. Maybe you can just start with every ground wire and find one that is not connected at the computer.
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Originally posted by Eds_Automotive View Post
I can see why you had so many problems, the 2006 is a big step from the 2003-2005 so that makes sense.
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So, small update, customer informed me that the transmission is stuck in 3rd gear, something I didnt notice last time I had my scanner on it. Is "3rd only" considered limp mode on the 4L80? Guy thinks that 2nd gear is limp mode but that the one that did the tuning might have done some 4L60 tuning to it or something.
Edit: we also realized my scanner will connect to the truck, and pulls codes no problem, but both trans and engine data stream say that it cant connect, which is weird.Last edited by Eds_Automotive; January 23, 2020, 07:02 PM.
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