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4L80/85E Transmissions. 6L90 Transmission Discuss the 4L80/85E transmissions found in the 6.2/6.5L equipped vehicles and Duramax equipped vans. 6L90 discussion.

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Old 06-03-2019, 02:15 PM   #11 (permalink)
Beastwerks
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Quote:
Originally Posted by johnH123 View Post
when I rebuilt my 4l80e, after about 4 days I had a shifting issue and p0756, shift solenoid error. After months of diagnosis, I pulled the trans and ripped it apart to find that the 2nd clutch lip seal had a big chunk missing, causing the computer to 'think' there was a shift solenoid issue. The moral of the story is that sometimes the computer is tricked into spitting out a code, but the thing it says is faulty is not the real cause of the issue.
I definitely take that lesson to heart, lots of the issues on this truck have been... convoluted to say the least. As far as this transmission goes, I took it into a shop that was recommended to me for a diagnosis. The guy hooked up his computer and drove it a little and said that he felt like it was an electrical issue. To him it sounded like it was shifting well when commanded, read that it was going up to 4th just fine when driving, and then he saw the power drop out to the transmission for a second which then threw it into limp mode immediately.

So, how do the lines to the trans run in the 6.5? I can see the wires running along the back of the engine, so I'll poke around in there and see if a wire is wearing, but what else is there? The guy said to check the ignition switch and even the computer, does that play out? How does that circuit route? I changed out the ignition switch only a few months ago trying to solve a different problem, so that's pretty new (not that it's good, just new). The PCM that's in there too was a refurb I got not too long ago when I ordered a redone chip, so I wouldn't necessarily think that was the problem. I have an old computer I pulled from a (I think) 1995 6.5 that had a manual behind it. Can I just swap the chips and drop that pcm in there to see if that's the cause without hurting anything?

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1994 C2500 w/ 350k miles (ooof), 8' bed and x-cab
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Old 06-03-2019, 03:11 PM   #12 (permalink)
Glagulator
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PINK or PNK/BLK wire from ign. sw. to TRANS fuse.
Then from TRANS fuse to bulkhead conn. position "A3"- top row near center.
Then to tranny connector.
Feeds the tranny only, nothing else on that feed with diesel.
Is your trans original, not rebuilt?
How does reverse work when cold and then when hot having the problems?
Codes do point to electrical.
Does the software tell you voltage on that feed, "E" as you are driving?
Unplug the tranny conn. and take out the trans fuse and check the pink wire for continuity to ground, checking for a short, while wiggling the harnesses.

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There are 10 kinds of people in this world; Those who understand binary and those who don't.

99 CREW LONG SRW C3500 work truck 199k+ mi. orig. motor & trans 4.10, modded engine harness, new oil cooler & lines, all new front end parts and poly bushings, trans poly mount, all new brakes.
96 SUBURBAN K2500 wife's truck 210k+ mi. orig. motor & trans, 3.73...
95 C2500 Suburban 6.5td HO w/p, timing set, HB & pulley, all rubber hoses, modded engine harness, PMD to bumper...
95 C1500 Suburban 6.5td rebuild tranny, convert to DB2, replacing as many parts as I can.
96 C2500 Suburban 7.4L converting to 6.5td w/ DB2, 4L80, 3.73
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Old 06-03-2019, 07:16 PM   #13 (permalink)
johnH123
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ignition switch could be an issue. They are known to fail and cause tranny issues, as crazy as that sounds.
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1993 K3500- 4x4, single cab/long bed, single rear wheels, 4.10 rear end, F vin, Nv4500 manual, factory red interior.


Gone but not forgotten: 2001 silverado 2500hd CC/SB, 4x4, 6.0 vortec, 229k miles when I traded it.
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Old 06-03-2019, 07:43 PM   #14 (permalink)
Beastwerks
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Quote:
Originally Posted by Glagulator View Post
Is your trans original, not rebuilt?
Okay, so providence is unknown. Previous owner told me he had it rebuilt "100k" ago, but I really don't know for sure. I've got 370k on the truck so I'd be pretty damn impressed if it was original.

Quote:
Originally Posted by Glagulator View Post
How does reverse work when cold and then when hot having the problems?
Reverse is just fine both hot and cold. I haven't gone tearing up the streets in it , but it's never given me problems.

Quote:
Originally Posted by Glagulator View Post
Does the software tell you voltage on that feed, "E" as you are driving?
That it doesn't do. I've got a few things I can look at, current gear, gear ratio, input and output rpms, solenoid duty cycle, so forth, but transmission 12v in is not one of them. I admit I was taking the auto guy on his word that was what he was reading on his test drive.

Quote:
Originally Posted by Glagulator View Post
Unplug the tranny conn. and take out the trans fuse and check the pink wire for continuity to ground, checking for a short, while wiggling the harnesses.
Okay, this is the results of that laid out...

Key ON, fuse IN, Tranny 12v power line "E" at 12.43ish volts to frame ground, test light lights up "E" to frame ground as a 2nd verification.

Key OFF, fuse OUT, Tranny 12v power line "E" at 0 volts to frame ground (even with jiggling), test light does not light up "E" to frame ground.

Key ON, fuse OUT, Tranny 12v power line "E" at 0 volts to frame ground (even with jiggling), test light does not light up "E" to frame ground.

Furthermore, I dug out my spare PCM and ignition switch. The truck runs and drives with both of those, still has limp mode using the spares as well. I'm beginning to narrow my suspicions down to the harness I spliced in or some of the other transmission signal wires. I say that since I did a different dtc testing.

I had the key ON, Engine OFF and read codes. Since this morning I'm now only at 81, 82, 83. I clear the codes and wait 15ish seconds. Read the codes again and I'm immediately at 81, 82, 83 without having started the car and driven around. Unless there's some other kind of memory I have to clear that's not in the PCM, I'm suspecting I either have a short or weak/intermittent connection that's confusing the computer right away and popping it into limp mode as soon as it's warm.

Now, my splices can totally have been bad, so I'll have to maybe redo that connector. However, to be thorough, after the harness snakes up the transmission it splices into the main harness right around the glow plug relay, I didn't see any obvious breaks/wear in those lines. I didn't see any obvious damage to the trans line as it comes through the firewall or snakes up to the ignition switch. But, while the 12v supply looks good, I dunno about the signal wires (the ones for the shifter solenoids, the valve relay, the temp gauge, etc.). After they splice into the main harness which way are they routed? Do they head along the firewall to the passenger side wire port? If they do head in that direction, do they happen to dip down near where the rear engine ground bolt is (the one by the trans dipstick tube)?
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Old 06-03-2019, 10:09 PM   #15 (permalink)
Glagulator
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Open this document and scroll down to the solenoid resistance values.
Check yours.
http://www.google.com/url?sa=t&rct=j...SRW5luTmzeAzm1
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There are 10 kinds of people in this world; Those who understand binary and those who don't.

99 CREW LONG SRW C3500 work truck 199k+ mi. orig. motor & trans 4.10, modded engine harness, new oil cooler & lines, all new front end parts and poly bushings, trans poly mount, all new brakes.
96 SUBURBAN K2500 wife's truck 210k+ mi. orig. motor & trans, 3.73...
95 C2500 Suburban 6.5td HO w/p, timing set, HB & pulley, all rubber hoses, modded engine harness, PMD to bumper...
95 C1500 Suburban 6.5td rebuild tranny, convert to DB2, replacing as many parts as I can.
96 C2500 Suburban 7.4L converting to 6.5td w/ DB2, 4L80, 3.73
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Old 06-07-2019, 01:26 PM   #16 (permalink)
Beastwerks
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(Hopefully this isn't a double post, I think I lost the 1st go around)

So I found time to crawl up under the truck and this is the results...

Shift 1-2, Pins A+E: 20.4ohm
Sift 2-3, Pins B+E: 20.4ohm
TCC, Pins S+E: 9.6ohm
PCS, Pins C+D: 4.2ohm
Temp, Pins M+L: 4.41Kohm
ISS: 1.35Kohm
OSS:1.37Kohm

All in a temperature of roughly 55*F. It seems like the internal electrical is okay, though I didn't test the pressure switch plate before putting that in (because I'm clever like that). It is new though, so I would hope it's good. I think I recall checking to see if I was getting the proper 12ish volts to ground on the harness side when I spliced the new harness in too. I'm mostly sure it's not the ignition switch at this point, I've tried a couple.

Where's the bulkhead connector for the lines that aren't the power-in line? Is that the one near the AC? I wanted to maybe trace and see if I've got some wires wearing through that could be causing a drop under load, I've definitely had that issue before with this beast.
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Old 06-07-2019, 03:47 PM   #17 (permalink)
Glagulator
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On your 94 all the tranny wires go thru the pass-thru bulkhead conn. on the pass. side EXCEPT the 12v. PINK wire. It is a pass-thru, not a connector.
I see the wires get worn where they come out and bend upwards quite often.
They rub on the inner fender, a/c lines and get hot from the exhaust.
At this point I would add a wire to the 12v. PINK where you spliced it and run it to the cab so you can monitor the voltage as you drive. The codes you are getting are triggered by voltages to the 3 solenoids that are not what the PCM is commanding.
It is not probable that there is a ground problem especially when a spare PCM was tried and the engine runs OK. All grounds in the PCM are tied together.
I cannot think of any mechanical problem that would cause those codes.
__________________
There are 10 kinds of people in this world; Those who understand binary and those who don't.

99 CREW LONG SRW C3500 work truck 199k+ mi. orig. motor & trans 4.10, modded engine harness, new oil cooler & lines, all new front end parts and poly bushings, trans poly mount, all new brakes.
96 SUBURBAN K2500 wife's truck 210k+ mi. orig. motor & trans, 3.73...
95 C2500 Suburban 6.5td HO w/p, timing set, HB & pulley, all rubber hoses, modded engine harness, PMD to bumper...
95 C1500 Suburban 6.5td rebuild tranny, convert to DB2, replacing as many parts as I can.
96 C2500 Suburban 7.4L converting to 6.5td w/ DB2, 4L80, 3.73
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Old 06-09-2019, 02:21 PM   #18 (permalink)
Beastwerks
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Quote:
Originally Posted by Glagulator View Post
On your 94 all the tranny wires go thru the pass-thru bulkhead conn. on the pass. side EXCEPT the 12v. PINK wire. It is a pass-thru, not a connector.
I see the wires get worn where they come out and bend upwards quite often.
They rub on the inner fender, a/c lines and get hot from the exhaust.
At this point I would add a wire to the 12v. PINK where you spliced it and run it to the cab so you can monitor the voltage as you drive. The codes you are getting are triggered by voltages to the 3 solenoids that are not what the PCM is commanding.
It is not probable that there is a ground problem especially when a spare PCM was tried and the engine runs OK. All grounds in the PCM are tied together.
I cannot think of any mechanical problem that would cause those codes.
Hmmm... So I maybe jumped the gun a little, but I figured I'd take potential issues with the 12v line out of the equation. I ran a fresh wire straight from the fusebox to the connector and spliced that into the 12v in, still getting the issue.

Okay, maybe my original splices on the connector are bad, redid those for the A, B, and S lines (Shift and TCC solenoids) while double and triple checking that I was getting next to no resistance at the splice before sealing it up. Also pulled the entire wiring back up to where it leaves the main harness at the top of the motor, stripped off the old shielding, and thoroughly checked the wires for wear and heat damage. It looks like some of the wires may have gotten a little hot for the temp sensor and maybe one for the pressure switches, but there were no real obvious breaks, the insulation looked intact. Put fresh shielding on it, wound it back down, hooked everything up, still getting same issue...

It's hard to tell if there's damage to any of the wiring at the pass through, but if there is it wouldn't change how I'd like to fix it. What I'd like to do is to splice new wiring in starting close to the computer and bypass all the crap in the engine bay entirely. Before I do that I'll make sure to test better if I'm getting a voltage brownout along that 12v in line by running a couple wires to test the voltage between the ground at the back of the motor and the wire I ran from the fusebox, and I'll run a wire from the transmission body to the frame's ground lug just in case.

If I go for the nuclear option (Insert Aliens Quote), does anyone have a diagram/really nice photos that show exactly which wires are which that go into the connectors for the computer? Focusing on the transmission, yes, but also maybe the computer's main ground terminal as well? I'd love to replace that with something appropriately sized that runs back to the battery.

In addition, is there any way that I could be getting a brownout before the fusebox? When I was running my fusebox line I derped and ground the wire end onto the frame and it popped the fuse pretty much immediately, which it wouldn't necessarily do if it had an intermittent ground on that wire before it hit the fusebox, right? I know this is probably an amateur hour question, but how is the power supplied in this truck? I know it goes battery--->block along the passenger side firewall (A line which I replaced because some genius wrapped the undersized wire around the exhaust), but from there how does it travel? Battery--->Firewall block--->???--->Ignition switch--->In-cab fusebox--->Trans 12v in--->appropriate solenoid--->back up the the computer which then opens/closes that line as needed--->ground lug at rear of engine--->battery? Something like that?

I know I'm learning this as I go, which is probably lots of fun for you guys . Seriously though, I deeply appreciate your input, the knowledge I've gotten from this forum has kept me and my truck working for a couple years now and has really saved my bacon.
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