4l60e electrical problem

Joined
Apr 9, 2021
Messages
10
Points
1
Location
Parts unknown
Make
GMC
Model
Suburban
Year
1997
Miles
260K
Engine
5.7
Hello all, Just joined the forum looking for some solid advice. A little about me. Retired GM auto worker, been wrenching 30 plus years, Owned and operated small salvage yard, Small engine repair shop, Stens parts dealer for many years, Worked for several automotive engineering and testing facilities, Ran full chassis dyno's for medium duty truck application's, spent some time on the assembly line at TMMK north American plant, etc.

Got this problem child suburban with the 4l60e trans in it. Picked it up cheep due to the transmission problem. No answers as of yet. And it's not for a lack of tring to fix this thing. Would be nice to determine something before changing the trans. With the transmission fuse pulled I should be able to shift through all the gears manually Correct ? Tested this in my other good truck and have all gears. 1234. Exact same thing 96 / 97 4l60e. However only have 3 and 4, drive and over drive in the problem child. What ever is going on has caused the transmission to turn off all forward gears, and acts like the gears are all neutral. Have to pull fuse, disconnect main trans connector, or force shift with the scanner. Only then moves in drive and over drive only, no 1 or 2. All electrical parts in trans have been replaced. Throttle position, and speed sensor have been replaced. Ecu has been replaced. Aftermarket alarm system has been removed. So why has this thing shut down the forward gears? Why no 1, and 2 ? Why no transmission codes?

Talked to several transmission shops to explore options. Answer is always the same. Trans is bad, that will be 2000 to 2500 dollars please. Would sure like a better explanation than that. Why is it bad? Why is the transmission shut it's self down? Why can I force the trans to turn on with my scanner? Why no 1 and 2 but 3,4 ? Because transmission is junk, is not an answer.
 

billr

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I sent you PM.

I am not a trans expert, be patient until one joins in; they are busy folks! However, I doubt you should get be able to get all gears manually with no power to the trans.

If you go back into the pan, I recommend you pull the VB and do air-checks on the clutch/band actuators. Have you done a check of line-pressure?
 

paulo57509

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Apr 9, 2014
Messages
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I'm not a transmission expert either but know enough to get into trouble. My approach would be to determine if it's an electrical or mechanical issue.

1. When selecting forward gear ranges (1-2-3 and OD) and the transmission acts like it's in neutral, does the transmission have reverse?

2. After pulling fuses and you get forward movement when OD or D is selected, does the transmission shift through all forward gears (does it shift through 1-2-3 and OD)? Or does the transmission not want to shift at all or seem like it starts in 3rd gear?

Before dropping the pan and replacing the electricals, what did the ATF look like? Other than a bit of fine black powder attached to the pan magnet, was there any other debris?

Did you replace the (TFP) Manual Valve Position Switch? How about the solenoid wiring harness and/or the electrical switch on the outside of the transmission attached to the manual shift linkage?
 

grcauto

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May 29, 2014
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What are the codes, if any? What kind of line pressure and regulated pressure do you see?
 
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Got your pm bill, that's some good info thanks. I'm no trans expert either, was kind of hoping to get some input from one of the experts. Tried posting in another forum, but just not specific enough. Liking that this forum is a trans specific one. You would think that an electronic transmission would need some power to make things work. No power defaults to full pressure is what I understand. I tested the fuse pulling thing on my old plow truck. A total ratty piece of junk, but transmission works perfectly. Have all the gears with no power going to the trans on that one. Not sure how good of a test, since no transmission issues on that one. But interesting findings to say the least. Pulled the trans pan like 4 times to swap parts out. Was thinking maybe valve body may be clogged up, or accumulator stuck. Yes I would like to check that line pressure, have not done that. Line persure in the 2 low gears vs the two high gears that work would tell me something. Getting tired of pulling that pan off for sure. Lots of advice to just pull trans and get unit bench overhauled. But would like to know what's really going on first. I have three good used transmissions that will fit this truck. I accually bought it because if the stock pile of transmissions. One way or the other thought I could fix it easily. Coming up on 2 years it's been sitting in my driveway. That's not a good thing.
 
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I'm not a transmission expert either but know enough to get into trouble. My approach would be to determine if it's an electrical or mechanical issue.

1. When selecting forward gear ranges (1-2-3 and OD) and the transmission acts like it's in neutral, does the transmission have reverse?

2. After pulling fuses and you get forward movement when OD or D is selected, does the transmission shift through all forward gears (does it shift through 1-2-3 and OD)? Or does the transmission not want to shift at all or seem like it starts in 3rd gear?

Before dropping the pan and replacing the electricals, what did the ATF look like? Other than a bit of fine black powder attached to the pan magnet, was there any other debris?

Did you replace the (TFP) Manual Valve Position Switch? How about the solenoid wiring harness and/or the electrical switch on the outside of the transmission attached to the manual shift linkage?
 
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Reverse works consistent with fuse installed or pulled. No forward gears at all with fuse installed. Acts like all gears are neutral. Pull the fuse and overdrive and drive works, just not 1 or 2 does act like it's holding in 1 and 2 though. Not getting any transmission codes. I need to look closer at the pressure believe my scanner has that info.
 
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I did replace all the electronic parts, all solenoids and the pressure manifold, including the internal wiring harness. Fluid had some debris, but not extremely horrible. Truck has some miles on it so expected some crud. Didn't replace the neutral safety switch. Don't really like to replace those where they glue the connector from the factory. Hard to get the connector loose without busting the switch apart.
 

billr

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Pressure is listed on page 9 of what I sent you. We have one trans expert here, owns a trans shop, who doesn't check in all the time. I'll summon him by PM if he doesn't show up by tomorrow morning.

The trans that works OK, what year is that vehicle? The 4L60/E has evolved a bit over the years. I don't think they are all identical. Again, I would not expect all gears to operate with no power to the trans; just R and one forward gear (3rd or 4th?) for a "limp-home" mode.

Do you have a scanner that shows trans live-data? If not, you are crippled here. You need to check things like "gear selected" and "gear commanded".
 
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Read many many posts on the limp mode. Mine seems to have skipped limp mode and just shut down completely. Would have to drive it in reverse to limp home. I stumbled across pulling the fuse thing by accident during my searches. Easier than getting the scanner out and fumbling though all the menu's. I like being able to move the truck around. Ok will check page 9 for the psi spec. Yes pass that info along to that trans guy if you would. Would be nice to get his perspective on this. That truck with the working trans is a 96 tahoe, problem child is a 97 suburban. I thought they were both the same trans. I have a hollandar program, will have to double check the interchange. Hollander is not always correct though. Scanner is a real cheep pos but does have some sneaky tricks. Have one free software I can add, haven't done that yet. Should have some more features to play around with then. Does have the transmission output controls, 4 different command states, can turn things on and off, some data available. Only psi readings are map and baro in the transmission section. For the 97 burban only the map psi increases when in gear and when you rev the engine. Sitting at 29 psi in gear at idle and runs up to 36 or so when rev the engine. Baro is at 95 and pretty much stays the same. Numbers look about the same on the 96 tahoe, when I scanned both trucks it this evening. Not sure if that even relates to the transmission, but the only thing labeled psi. Will try running regular live data some tomorrow to see if I can see anything else. Mosquitoes were bad tonight and they ran me off. This scanner has a goofy layout for sure. But much better than the last four scanners.
 

billr

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Those MAP/BARO numbers only make sense if they are in kPa (kilo Pascals), not psi. If your scanner is really labeled in psi for those readings, I already don't trust it...
 
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