4L80E swap problems

I had a customer bring in a 2007 Silverado 1500 that had a 4L80E swapped into it. The truck is running an E38 ECM and a T42 TCM. When he originally had the transmission installed, he said the truck would shift into overdrive and lock the torque converter, but the PRNDL display on the dash would not indicate what gear it was in until he had the truck tuned. Now the shifter display works, but it doesn't go into overdrive or lock the converter. I tried flashing in a stock T42 4L80E tune that I found on the forum from an Express van, but that didn't fix the problem. I also tried flashing in a 4L60E tune, and that put it in default safe limp mode or whatever you want to call it.

Anyone have any idea what could be going on? Any help would be appreciated.

Has the wiring harness been altered such that it mirrors an original OEM Gen IV engine and 4L80 combination ? Or are you using an adapter harness of some sort ?

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Originally Posted by Taz

Has the wiring harness been altered such that it mirrors an original OEM Gen IV engine and 4L80 combination ? Or are you using an adapter harness of some sort ?

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I honestly don't know what has been done to it. I only looked under it to see that it has the input speed sensor on the front of the case just behind the bellhousing connected with butt connectors. Could there be something in the ECM that is preventing this? The engine is an L76 6.0 with DoD. He said he had the truck tuned before he had the 4L80 put in with the DoD disabled, but when he got it back the DoD was back on. After he had it retuned, the truck would no longer go into overdrive or lock the converter. I don't think it's because of something in the TCM tune, but is it possible it could be something in the ECM?

OK ... in post #1 you used the word "customer" - which implies you run a business of some sort. Standard operating procedure as a reputable tuner is to confirm what has been done / changed / installed by the owner or another shop prior to the vehicle being brought to you.

In this case, obtain 2007 T42 pinouts for both a 4L60/65/70 and a 4L80. Then confirm where each pin in the main transmission connector, VSS connector, and ISS connector are routed to, with respect to the TCM connector. Once you determine if there is, or is not, an issue with the wiring, then move on to the calibrations.

My two cents is to always start fresh with respect to the calibrations. I would flash the ECM and TCM back to their OEM stock calibrations, and then tune from this point. Obviously this would put a 4L60/65 tune back in the TCM - but that is OK (actually necessary) to establish appropriate communications with the ECM / IPC, etc.

If you go this route, post the tunes (something you omitted to do thus far), and I will help you morph the 4L60 tune into a 4L80 tune, if that is what you require.

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Originally Posted by Taz

OK ... in post #1 you used the word "customer" - which implies you run a business of some sort. Standard operating procedure as a reputable tuner is to confirm what has been done / changed / installed by the owner or another shop prior to the vehicle being brought to you.

In this case, obtain 2007 T42 pinouts for both a 4L60/65/70 and a 4L80. Then confirm where each pin in the main transmission connector, VSS connector, and ISS connector are routed to, with respect to the TCM connector. Once you determine if there is, or is not, an issue with the wiring, then move on to the calibrations.

My two cents is to always start fresh with respect to the calibrations. I would flash the ECM and TCM back to their OEM stock calibrations, and then tune from this point. Obviously this would put a 4L60/65 tune back in the TCM - but that is OK (actually necessary) to establish appropriate communications with the ECM / IPC, etc.

If you go this route, post the tunes (something you omitted to do thus far), and I will help you morph the 4L60 tune into a 4L80 tune, if that is what you require.

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I do. The problem is the owner of the truck doesn't know anything. When he called me he asked if I could flash a tune in the TCM because he had it tuned and now it doesn't shift into OD. I obtained a stock T42 4L80E tune file so I could flash the TCM with a stock tune. I didn't have time to pull it up on the lift and go over everything with a fine tooth comb, and when I asked him what was done as far as wiring goes, he said he didn't know. I asked him if he took it back to the guy who installed the transmission, and he said he had it for a few days and couldn't figure it out. I told him to bring it back, and I would spend more time going over all the wiring and everything. I just thought someone might know what could have been done in a tune to cause it not to work. I generally don't believe in coincidences like this, but maybe that's the case here. I don't have the tune in the ECM because I didn't really consider that a possibility, but I'm no expert on E38 tunes so I thought maybe somehow it's possible. I'll post the tunes I have, but they're on another computer.

By the way, I appreciate your help.

Maybe he is wrong and it never worked properly?

Owner history is good, now I have an idea where to look for the problems... Taz has it right, time to look it over pin by pin and see what your working on.

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I only looked under it to see that it has the input speed sensor on the front of the case just behind the bellhousing connected with butt connectors.

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Butt connectors are all I needed to see before I'd have to look it over pin by pin...

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Originally Posted by JoshH

I only looked under it to see that it has the input speed sensor on the front of the case just behind the bellhousing connected with butt connectors.

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I agree, this is indicative that the harness may have various other problems.

Whomever worked on the harness before really does not have any excuse/reason for not working on the harness correctly, it is far too important to take shortcuts on.

I agree with both of you. I cringed when I saw the butt connectors and knew I didn't have the time to go over the wiring right then. Here is the TCM tune that was in it and the stock 4L80 tune I tried.

Attachment 16500

Attachment 16501