4L60E no shift

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Mason Cramer

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I have a '96 K1500 with a 5.7L L31 and a 4L60E. Just finished putting in the motor after rebuilding it. While it was out I changed the filter and ATF and drained and refilled the torque converter. The transmission is now in some sort of limp mode. My understanding of a 4L60e is that "limp mode" is stuck in 2ns gear. My tranny is stuck in 1st and I also have no speedometer. I can manually shift to second on the column but 3rd gear on the column goes back to 1st gear. Drive leaves it in 1st gear and when it would normally shift the ABS light on the dash turns on and it will not shift to any gear. My next step was to plug in my scanner and see what was the issue. I am able to view exactly what gear the transmission is in, and can even manually shift the transmission through my scanner. 1st - 4th without an issue. That pretty much isolated anything inside the transmission in regards to the solenoids and actual gears. I can also manually turn on and off the solenoids and they work. The TCC also works. My next step was to look at all the sensors that are inputs and outputs to the TCM. To my understanding that would be the VSS, the TPS and the MAF. I replaced the VSS because it was easy and considering my speedometer wasn't working I thought it might have been the culprit but it did nothing. MAF is clean and I would say it is working as the engine dies when I unplug it and do not get any codes until I do. The TPS is what I'm most concerned about considering I've had random issues with it in the past. Always had an issue with the truck stuttering after turning off an an exit on the highway and have to Floor it to get it to reset. My scanner shows no issue with the TPS and the TPA and when I test it on my workbench with a meter and a bench power supply it works great. Another thing to note is that my EGR pipe broke about a year ago and welded all of my wiring harness together. Because I could not find another 96 L31 harness that wasn't $1000 I took the fun job of soldering and heat shrinking about 140 connections on the entire wiring harness. I did not have any issues after that other than that random TPS light and stuttering ever so often. I've tried checking PCM connections, checking Transmission wiring, and connectors and have absolutely no idea why it's not shifting. The ABS light confuses me as well. I cannot find anywhere where the ABS system is connected to the TCM. Any ideas would be appreciated. I'm about to go buy a TCI slap shifter and manually shift this transmission with a few modded toggle switches and run it full line pressure. I would rather put it back to normal but its my backup plan lol. Thanks
-Mason
 
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sntrym

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If you took the tranny out too, it sounds like there's an electrical connector that didn't get hooked back up. I'd look around for that, and make sure all the grounds went back in the way they were.
 

Mason Cramer

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I didn't take the transmission out. Only thing I did was take the pan off to change the filter and drain the torque converter. Never touched the PCM or the wiring while the engine was pulled. The grounds for the battery to body, battery to block, block to frame and frame to body are all new connections from when I resoldered the wiring harness
 

sntrym

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I would start looking for a short in the splices from the harness melting. It defintely sounds electrical and maybe removing the engine and bending the wires caused either a short or a wire to break internally.
 

sntrym

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Also, check the fuse for the MAF, O2, etc. The trans runs off that and if an O2 sensor blows the fuse, then it will cause the trans to go into limp mode. Also:
 

Schurkey

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I have a '96 K1500 with a 5.7L L31 and a 4L60E... ...My tranny is stuck in 1st and I also have no speedometer... ... when it would normally shift the ABS light on the dash turns on and it will not shift to any gear. My next step was to plug in my scanner... ...My next step was to look at all the sensors that are inputs and outputs to the TCM. To my understanding that would be the VSS, the TPS and the MAF. I replaced the VSS because it was easy and considering my speedometer wasn't working... ...The ABS light confuses me as well. I cannot find anywhere where the ABS system is connected to the TCM.
The VSS enables the transmission shifting, the speedometer, and the ABS--it's the "speed sensor" for the rear wheels.

On my '88, the signal from the VSS goes to the instrument cluster. The IC processes the VSS signal, sending it to the cruise control, ABS, speedometer, odometer, and the vehicle computer for use in computing fuel and spark needs. I don't know how much your '96 has in common with my '88.

Figure out:
1. Is the VSS sending a proper signal,
2. Where is the VSS sending the signal to? Instrument cluster? Vehicle computer? Body computer?
3. Is that component actually receiving that signal?
4. Does that component pass the signal elsewhere? Does the next component in the chain receive the signal?
 
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Mason Cramer

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Also, check the fuse for the MAF, O2, etc. The trans runs off that and if an O2 sensor blows the fuse, then it will cause the trans to go into limp mode. Also:
Every fuse in the vehicle is fine. Swapped all of the ECM, ENG and Trans fuses just in case. I have ran through the entire wiring harness up until it reaches the PCM and fuse block and found no issues. Checked all my joints and they still appear to be fine.
 
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