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Old 03-04-2019, 09:40 AM   #1
FL72GMC
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4L60 stuck in Limp mode

Just completed my 2002 5.3 / 4L60 swap into my 72 GMC and the trans seems to be stuck in limp mode. Reverse and 2nd, 3rd while in drive. I have power to the trans but no error codes to the computer. I have not hooked up the TCC but I don't think that would put it in limp mode. Fluid is good and I everything is hooked up correctly. Any suggestions? I am at the point of sending the computer to be programmed to see if the issue is there. I would think I should get some error from the trans if there is a problem.
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Old 03-04-2019, 10:25 AM   #2
ls1nova71
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Re: 4L60 stuck in Limp mode

Did the trans work before the swap? Doubt it's a computer issue.
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Old 03-04-2019, 11:21 AM   #3
FL72GMC
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The engine and trans came from separate vehicles. Buddy of mine put them together, modified the harness, and reprogrammed the pcm.
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Old 03-04-2019, 12:05 PM   #4
FL72GMC
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The engine and trans came from separate vehicles. Buddy of mine put them together, modified the harness, and reprogrammed the pcm.
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Old 03-05-2019, 10:46 AM   #5
BR3W CITY
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Re: 4L60 stuck in Limp mode

Trans error won't always pop codes, trans codes themselves won't appear on all types of scanners. If your friend tuned it he should be able to command specific gears in HP tuners and see if it complies.
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Old 03-05-2019, 12:33 PM   #6
Wgesnerjr
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Re: 4L60 stuck in Limp mode

On the LT1 Swap page he talks about one circuit that feeds the transmission solenoids.
http://www.lt1swap.com/underhoodfuseblock.htm
I forgot to wire this on my swap and it felt sluggish. Like starting in second gear. Once I dove into it and wired the circuit up correctly, my truck runs great!
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