1999 Tahoe Stalling Issue

[Eds_Automotive]

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.

[anotheridiot]

I can see why you had so many problems, the 2006 is a big step from the 2003-2005 so that makes sense.

we live and learn, figure same motor, same trans, same knob for the 4wd engagement same body style. I guess I would have learned the connector was different if I checked a little deeper, but when you are on your back in a muddy yard and figure to cut wires since the damn connector wont come out. The neutral safety switch had one long gray connector instead of the two or three smaller ones that give us so much trouble on the van, so I was glad to leave that alone.

[Dan Barlow]

There are changes in how they are wired for the solenoids and such( 4L60E ) I don't know what the difference per year but I was advised by a friend at work that the 94 and 95 are the same so both times I needed one that's what I shopped for .

[Eds_Automotive]

what are the voltages from the TPS?

Last time I checked, the TPS was sweeping normally as I applied the throttle in the datastream. Ill check again in the morning

[Eds_Automotive]

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.

I can see why you had so many problems, the 2006 is a big step from the 2003-2005 so that makes sense. On this one, the range switch only has two connectors, one of them goes to the computer, the other one goes to the dash and is only for the indicator on the dash, far as I can tell it dosnt need the indicator to work to be able to run, I tried the 4L60 switch because it was the same as the 4L80, no luck. Even tried a brand new one for the 4L80 and it didnt fix the code either. I went back and checked the trans wires going into the PCM and there was no continuity issues and they were where they should be. This PCM is the upgraded one with two 70+ pins as opposed to the older one that had 4 connectors. Yes, he had some issues with it not shifting into OD, but the rest of the trans was working properly. When I get some time I want to check the grounds at the PCM before talking to him about sending the PCM back to the tuner so he can remove the range switch and just eliminate the code altogether. From there I should be able to do the crank relearn procedure and if it still acts up then I know its something else.

[SuperBuickGuy]

what are the voltages from the TPS?

[anotheridiot]

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.

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.

[Eds_Automotive]

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?

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.

[anotheridiot]

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?

[Eds_Automotive]

A locked up converter, is like stopping vehicle without pushing on the clutch, it'll stall it.

But would this occur ONLY when you let off the throttle? I can rev it to the moon and back in park, its only in gear under a load and only when you let off it.

[Eric]

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.

A locked up converter, is like stopping vehicle without pushing on the clutch, it'll stall it.

[Eds_Automotive]

The truck stock, controlled the ign through the ecu.
You don't say if this 454 is a tbi and computer controlled distributor ign , or a csrb and mechanical timing with vac advanced can distributor.
THe 350 ecu is not going to fuel and ing advanced maps correctly for a tbi 454.
and the 350's fuel system, the fuel pump is to high of pressure if it is using a carb.
Those trucks go into a limp home mode also. if (iirc) the pink wire going into the transmission looses power from the ign switch.

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.

[Eds_Automotive]

If the vehicle has transmission codes and you want to fix it 'properly' then you need to find out what the codes are before you go any further. The ECM talks to the trans, and if they're not having a good conversation you're going to have issues..

Another thing to consider,.. motorhomes spend a lot of time idling and pulling around a lot of weight.
Parts tend to wear out faster if the motorhome is actually driven, especially in warm states where they're driven year round.
Maintenance wise you have to treat a motorhome like a medium duty truck because that's what it essentially is.

You can check for easy stuff now sans retrieving the trans code. From the symptoms you've described I'd check the following items..

Try this first.. IAC solenoid. Pull the IAC and check for a carboned port/pintle, and clean everything thoroughly with carb cleaner.
A carboned up IAC and IAC port will cause the issues you're describing.

Vacuum lines. They're always overlooked, check ALL of them.

MAP sensor. Make sure it's working, and not broken, cracked, and make sure the vacuum line going to it is good.
A faulty MAP sensor can and will stall an engine.


Check the timing and check the timing chain for slop.
Hook up a timing light and do an initial reading in park at idle.
Then have someone put the vehicle in gear, and see where the timing marks end up.
Pull the distributor cap and turn the crank pulley back & forth to check for excessive play, lag in the distributor Vs the amount the crank is being turned.
A sloppy chain will throw the timing off enough to stall an engine in gear.

Torque converter, lock up solenoid. It's been said here already because it can and will cause the issues you've described. Pull the pan and check for debris.

The codes, as stated, are for the "trans range switch" and the crank relearn. The trans switch wont go away for some reason to be able to do the crank relearn but it ran for a while no problem until recently. All the things you suggest seem like something that will sputter and stall gradually, what Im experiencing is the ignition completely cutting off like a light switch the instant you let off the gas over like 1500RPM. Engine is very strong and has a lot of newer parts in it that got swapped over when we put the engine in it. Fortunately almost all the 350 parts like ICM, coil, distributor, etc fit no problem. Transmission may be where we are heading but I'm not sure if its going to be internal mechanical or electronic. The guy that tuned it says he can take out the range switch so we can do the crank relearn but Im not entirely convinced thats the issue yet, just a secondary problem. The odd thing is that I can put it in gear and hold it under a load as long as I want and it will sit there and take it no problem. Let off the gas, engine cuts straight to zero and dies. Darndest thing I ever did see.

[Eds_Automotive]

He's running it off off 0411 computer which I think goes to a 5.3 LS motor with a automatic. That's about all I'm good for . Well other than say run it off a aftermarket engine management system .

The auto detect on my scanner pulls it up as a 1999 Tahoe 5.7, I think its an LS1 map, maybe. Not sure how they do it.

[tardis454]

If the vehicle has transmission codes and you want to fix it 'properly' then you need to find out what the codes are before you go any further. The ECM talks to the trans, and if they're not having a good conversation you're going to have issues..

Another thing to consider,.. motorhomes spend a lot of time idling and pulling around a lot of weight.
Parts tend to wear out faster if the motorhome is actually driven, especially in warm states where they're driven year round.
Maintenance wise you have to treat a motorhome like a medium duty truck because that's what it essentially is.

You can check for easy stuff now sans retrieving the trans code. From the symptoms you've described I'd check the following items..

Try this first.. IAC solenoid. Pull the IAC and check for a carboned port/pintle, and clean everything thoroughly with carb cleaner.
A carboned up IAC and IAC port will cause the issues you're describing.

Vacuum lines. They're always overlooked, check ALL of them.

MAP sensor. Make sure it's working, and not broken, cracked, and make sure the vacuum line going to it is good.
A faulty MAP sensor can and will stall an engine.


Check the timing and check the timing chain for slop.
Hook up a timing light and do an initial reading in park at idle.
Then have someone put the vehicle in gear, and see where the timing marks end up.
Pull the distributor cap and turn the crank pulley back & forth to check for excessive play, lag in the distributor Vs the amount the crank is being turned.
A sloppy chain will throw the timing off enough to stall an engine in gear.

Torque converter, lock up solenoid. It's been said here already because it can and will cause the issues you've described. Pull the pan and check for debris.