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Sorry another 4l60e limp mode question, I read hundreds of posts before asking so bare with me ,, swapped a LM7 & 4L60E into my 82 C10 using factory donor harness modified to standalone has a blue/green delphi pcm , now pcm reflashed & has all trans info etc , but pretty sure its in limp mode feels like its labouring in drive & taking of in third, Has only has one other gear maybe 2nd. i checked the round trans plug it has 12,4v at the pink wire, I swapped to another trans today to be sure its not the trans itself , still same issues on second trans . codes throwing are p2761 p0758 & p0740 same codes on both trans ,, will ad the c100 plug has not been used in any way on the harness mod,, I'm guessing its got to be electrical with it being the same on 2 different units but where do I start..
Sounds like you are constantly in Torque Converter Clutch Lockup mode. Do you have a multi-pole brake light switch that supports killing power to the TCC when the brakes are applied? Your brake light switch from 1982 won't have this feature.
Sounds like you are constantly in Torque Converter Clutch Lockup mode. Do you have a multi-pole brake light switch that supports killing power to the TCC when the brakes are applied? Your brake light switch from 1982 won't have this feature.
Rick
i thought the brake switch may of been the issue i found the purple wire & hooked it to 12v ( as it would be without the brake applied to drive it see it it made a difference, obviously it was constant & not shutting off when braking but made no difference to operation.
Engine & pcm are from 2004 silverado 1500 , trans is from a 05 holden commodore ( aussie pontiac) pcm has been reflashed etc, i can scsn codes myself all converter clutch & shift solenoid related, but its the same with two alternative transmissions, so im picking wiring , the loom was already chopped up to run stand alone so my conclusion is a wire not getting signal or ground maybe. It has 12.4v at the pink wire to the round trans plug but maybe no ground .
Just so you know (Since you seemed uncertain if the Transmission was making a shift or not)...
In "Limp Mode" ...The Transmission Line Pressure will be at Full Pressure all of the Time.
Performing the Line Pressure Test (as I recommended) would help to clarify if the Unit was or was not in "Limp Mode".
I do not just make up these recommendations on a whim...
I was actually an Engineer for GM Transmissions for many years (and do still know what I am talking about).
Last edited by vorteciroc; Mar 16, 2024 at 06:17 PM.
Here is a full description from the GM 4L60E Technician guide for limp mode. I have also attached the code diagnostics for the 3 codes you shared.
I never test pin "E" for voltage I always test it for it's ability to carry a load. This test tool i made work very well.
Just so you know (Since you seemed uncertain if the Transmission was making a shift or not)...
In "Limp Mode" ...The Transmission Line Pressure will be at Full Pressure all of the Time.
Performing the Line Pressure Test (as I recommended) would help to clarify if the Unit was or was not in "Limp Mode".
I do not just make up these recommendations on a whim...
I was actually an Engineer for GM Transmissions for many years (and do still know what I am talking about).
No worries appreciate your , Im not uncertain its not making shift I know its not only has 2 gears , when in drive it feels like 3rd labours to take off & does not shift to anything else , Manual shift it to first second or third it is a lower gear im guessing second but its the same gear across all 3 shifts, ,Ill check the line pressure & confirm cheers
ok been a couple of weeks of changes ,swapped the complete chopped up factory loom to an over the counter stand alone one ,, few hicups connector wise but sorted it all in the end BUT still having trans issues , its no longer in limp mode , shifts 1 to 2 smooth as in drive but goes to shift to 3rd around 30pmh & hits no mans land {neutral} let my foot of it & back on it drops back to 2nd if I plant it kicks down to first etc,, had a mate with a scanner come for a drive scanner shows no codes , shows it command 1 2 solenoid then commands 3rd but nothing then tries for 4th , had the pcm checked & all software checks out ,, sooo am I now dealing with a good 3/4 clutch in the trans ?? & my inital issue was most probably wiring , I'm thinking I should try the first trans again
so this is truly messing with my head now,, swapped back to the original trans {the one stuck in limp mode on original post } thought having the new harness it may have gotten rid of the limp mode symptoms & it has ,, but take of in drive it has first no shift to 2nd or any further , no codes up at all if you throttle off it shifted to third & kicks down when feeding it to it.
so one trans smooth shift 1st to 2nd but no third just hit no mans land & the other has first & can throttle blip it to shift to third , no codes up on either all wiring & pin outs are correct trans1 commands 3rd gear shift when it tries hits neutral ,, didnt have the scanner here while driving trans 2 both fitted with converters that came with them .am i missing something else or just got 2 cooked transmissions
Are both transmissions used? Need to scan the 2nd trans to see if it is commanding the 1-2 shift. You can check the servo pin travel to see if it is excessive. See attachment for instructions.
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Lm7 & 4l60E swap trans issues 
