Help! 4l80 swap , won't crank over and no shift indicator light?
 

Hey guys,
Did some searching, no help, I do find 90% of my questions answered that route , anyways I got a 2009 Silverado 1500 (had 4.8l 4l60 stock). I swapped in a 08 ly6 and a 4l80e, I used a plug and play harness from a company called PCM of NC and it is supposed to take care of the wiring. Anyways, long story short I adjusted my tune as nessesary and went to start it, it wouldn't even crank.

I thought it was battery, boosted, still no, checked connections to starter, they all look good. I did paint a lot of the parts on the engine and starter, everything basically, maybe a ground problem? But I am leaning toward the trans shift Indicator- there is NO Way to tell what gear I'm in, I can see the PNRD321 but there is no line below like there was before with the old trans?

It also is behaving exactly like it would if it were in Gear, all the lights, everything is normal , just won't crank.

Any ideas?

Do you have a "PRNDL" switch on the shifter shaft coming out of the trans? Not sure if 09 has it. Thought they went internal in later years. My 07 does have an external switch. If the truck doesn't see Park, makes sense as to why it won't start. If you have one, they are slotted and can move. If it was internal in the 4l60, you're going to have to provide those signals now.

Hope this makes some sense.

I did a bit of digging , your definitely right. My old trans had an internal PNRD switch, and this 4l80 woulda had an external, attaching the switch no problem, but how in the heck do u wire it up??

Hate to say, but you're probably going to have to look up the wiring for both and make the change to an external sensor. 4l80 you're using will need the longer shifter shaft as the PRNDL switch mounts on it.

You could call a company such as Speartech to see if they could create a split out harness and get the PRNDL wires into a plug for the added switch.

Thanks so much for your help, you turned me in the direction I needed to go!

Still doing some digging, the company I got my harness from didn't answer the phone all day, musta been closed. I'll try tomorrow. I'm thinking I might need a full 2008 ecm and harness? Hope not. I wish my trans builder woulda had more intel for me. This is a nightmare.

Try searching your years here for wiring diagram.
www.revbase.com/BBBMotor/Wd
Search under transmission and controls.

I would think you could use the existing wiring in the harness that olugs into the 09 4l60e. Would have to remove the wires from plug and add the new external PRNDL switch.

Hit up PCMofNC since that's where you got your harness. Maybe they have done or come across this.

So I spoke to pcm of nc today, he said the harness they sell for 09-12 models will work, it has exactly what you said, the exaisting wires shot off into an pigtail for a external PNRD switch. So fingers crossed, this was all a hasty error on my part ( ordering the wrong part) I'll know next week when the part gets here.

One more thing I'm wondering, supposedly the gen 4 ecm don't need a segment swap, I just adjust a few parameters then set my shift points? Does that sound correct to anyone who may have done a gen 4 swap 60 to 80??

Thanks guys. Hopefully this can clear up some info for future users.

I believe you don't need a segment swap with their harness. My friend has one on his truck and you just follow their instructions on what parameters in your 4l60 tune you adjust.

Also, make sure your 4l80 has the longer shifter shaft on it to accommodate the external PRNDL switch.

Good luck. Let us know.

Running the PCM harness on my swap as well - pretty straight forward.