2002 Tahoe 5.3 Won't Start After 4l60e Swap - LS1TECH - Camaro and Firebird Forum Discussion

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2002 Tahoe 5.3 Won't Start After 4l60e Swap

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Old 08-30-2015, 12:41 PM
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Default 2002 Tahoe 5.3 Won't Start After 4l60e Swap

Hey all,

On Friday I had my junk tranny swapped out for a nice rebuilt from a reputable local shop. After getting everything put back together, we could not get the truck started.

First thought was the NSS, as these break all the time when swapping transmissions in these trucks. So we replaced that. Still won't start. We checked all the fuses and nothing is blown. The security light is only flashing when the truck is locked/unlocked or the door is open, per usual. It's not staying on so I don't think this is a security issue?

When the key is in the ignition and turned to ACC, all the dash lights come on, fuel gauge goes to where it should, and the headlights come one. When I turn to start, however, the lights for the gear selector go out until the key is turned back. The headlights do not dim and the volts do not drop.

Then we decided to try to put power right to the starter. When we did this it cranked right over and fired up only to immediately shut off. The key was in the run position. It fired up for us multiple times but also died each time.

My thoughts are that this may be the ignition switch? How would I go about testing that? I have no idea which of the dozen or so wires goes to what. I don't think it's a security issue as this truck has Passlock, which would cut the fuel, not the ignition. And I know it's getting fuel because it has started multiple times. If Passlock were activated it would not start at all.


The truck is currently sitting an hour from home at another shop that I'm not familiar with, although I have heard good things about. I'm not sure I trust the guy as he told me to bring it by Friday and that he would look at it then, but then didn't have enough time. He also apparently didn't have time on Saturday (he was open) an hasn't returned my calls. Hopefully he gets to it tomorrow or I'll have it towed elsewhere. He should have told me from the start he was jammed and couldn't look at it until after the weekend. It puts me in a position where I'm screwed because I can't even go troubleshoot the truck myself if I wanted to.


Any input, ideas or recommendation are greatly appreciated. I'm pretty stumped at the moment.

Last edited by ddes; 08-30-2015 at 12:46 PM.
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Old 08-30-2015, 08:24 PM
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Outside the trans, surrounding the shifter shaft you will typically find a box with a bunch of wires. This box performs is a safety switch to ensure you can only start in Park/Neutral; it also enables the backup lights in Reverse. It also signals the PCM whether you are in Park/Neutral.
Therefore, I suspect that this box was installed incorrectly, was broken, or your shift linkage is misadjusted. Start by seeing if the reverse lights work.
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Old 08-07-2018, 09:10 PM
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Anyone have any other ideas on this? I have a Sierra 1500 with the same exact thing going on and can't figure out why. Currently I can start the truck and run it just fine if I start it off the starter relay under the hood. I have reverse lights so my NSS seems to be fine..?
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Old 08-08-2018, 07:26 AM
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My issue ended up being the pigtail for the NSS. There was a small rats nest above the transmission, and at some point the rats must have chewed some wires. Never caused an issue until things got moved around when the transmission was removed/installed.
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Old 08-10-2018, 05:40 PM
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I see. Thank you for the advice, hopefully I'll get it figured out and fixed up soon!
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