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4l80e transmission electrical problems

01-25-2006, 04:00 PM
I have a 95 chevy 3/4 ton with one beautiful transmission. I purchased it from a guy who gave up on fixing it. He said that he had the transmission rebuilt, and also tried replacing the computer with no success. The transmission works fine part of the time, but the rest of the time it's stuck in 2nd. I checked the harness underneath, and found a couple of frayed wires, but not cut in two. They both looked to be pink. I fixed them, and nothing changed. I pulled out my trusty test light and found that my transmission fuse (#20) had no power going to it. I figured just to test it out, I would power up the fuse and see if the transmission would run right. Needless to say it didn't. Could the ignition switch be the guilty party in this nightmare? If anyone has an idea, I'd sure like to hear it.

01-25-2006, 04:56 PM
There is a tsb on this problem:
TSB# 01-07-30-002D

Malfunction Indicator Lamp On, Transmission Stuck in Second or Third Gear, Instrument Cluster Inoperative.

04-05 Rainier
99-00 Escalade
02-05 Escalade and EXT
03-05 ESV
97-99 Chevy/GMC Full Size; Pickup, Suburban, Tahoe (Yukon) (Old Style)
97-05 Blazer (Jimmy), (Bravada), Corvette, Express (Savana), S10 (Sanoma)
99-05 Silverado (Serria) (New Style)
00-05 Suburban, Tahoe, Yukon, Yukon XL
02-05 Avalanche, Trailblazer, EXT, Envoy, XL, XUV
04-05 Colorado/ Canyon
03-05 H2
04-05 GTO
With 4L60-E, 4L65-E, 4L80-E or 4L85-E

Condition: One or more of the following problems:
- The Malfunction Indicator Lamp is on.
- The transmission is defaulted to second gear (4L80/85-E).
- The transmission is defaulted to third gear (4L60/65-E).
- The instrument cluster is inoperative.

Possible DTC’s: P0720, P0753, P0758, P0785, P0787, P0973, P0976, P1860, P2761, P2764, and P2769 may be set depending on the vehicle.

Cause: The most likely cause of this condition may be a loss of voltage to the transmission on circuit 1020. This loss of power may be caused by an open in the ignition switch. This condition my also be the result of an incorrect installation of an aftermarket electronic device such as a remote starter or alarm system.

Correction: With the ignition switch in the RUN position, test for battery voltage at the appropriate fuse listed below.
97 S/T Trans 24
98-05 S/T Cluster 11
02-05 S/T Ignition 0
97-00 C/K(Old) Trans 20
99-05 C/K(New) Ignition 0
97-02 G-Van Trans 20
03-05 G, H-Van Ignition 0
03-05 H2 Ignition 0
04-05 GTO Auto Trans
97-04 Corvette Enging 1
05 Corvette ACC/TCM
04-05 Colorado/Canyon Trans

If the battery voltage is present at the fuse, inspect the ignition voltage circuit between the fuse and the transmission for possible opens. If the battery voltage is not present at the fuse, replace the ignition switch.

If the vehicle is equipped with an aftermarket electronic device and the DTC’s are being set when the device is being used, verify that the appropriate fuse listed above is being supplied battery voltage during operation. If voltage is not present at this fuse, these DTC’s will be set due to lack of voltage at the solenoids. This condition is most likely to occur with an incorrectly installed remote starting system. If this is the case, refer the customer to the installer of they system for corrections.

01-25-2006, 05:02 PM
No service engine light exists, I've probably checked it 5 times. Also, the tsb is too new to apply to my vehicle. What gives power to fuse #20?

01-25-2006, 05:16 PM
No service engine light exists, I've probably checked it 5 times. Also, the tsb is too new to apply to my vehicle. What gives power to fuse #20?

I don't have anything showing what gives power to that fuse, it is either constant or through the ignition switch. Sorry should have paid more attention to the year.

01-25-2006, 06:16 PM
Fuse 20 trans/instrument cluster fuse gets power from the yellow start/run wire from the ign switch. Is anything out on dash?
Check this link for a pdf on trans wiring.
If it is blowing trans fuse check for short going to or inside trans. And check the trans plug in for oil in it.

01-26-2006, 08:13 AM
That wiring diagram is the same one that I have, only mine has highlighter marks all over it. In the datastream, when it is stuck in 2nd, all the solenoids read off. The PRNDL still reads like it is working, but only with the engine running. When the KOEO (key on engine off), it reads to be in D2. The engine RPM's are also off KOEO (9999 RPMS).
Another odd thing that I noticed is that the Speedometer and speed the computer reads don't correlate when the trans. isn't working right.

01-26-2006, 08:21 AM
This morning, checked the trans. fuse for power and it had it. I hate intermittents.

01-26-2006, 08:45 AM
Check the shift solinoids inside the transmission. Solinoid B went out on my 94 camaro (4l60e) and mine would'nt shift out of third gear, solinoid A should could be bad holding it in second gear. It should have a code show up though if one was bad.

01-26-2006, 09:03 AM
This morning, checked the trans. fuse for power and it had it. I hate intermittents.
10-4 on the intermittents.
If you are losing power at that fuse.
I would hook a good 12-volt power source to the fuse and see if that helps and/or get a volt meter on it and see if it is losing power or voltage at times.

01-26-2006, 09:31 AM
Well, I got sick of guessing about where to start, I hate pulling tranny pans, so I decided to start with the power source, the ignition switch. I pulled the column apart, and got the trans fuse to lose power again. While holding my test light on the trans fuse, I tapped on the ignition switch with my screwdriver handle, and got the light to flash a little, so the ignition switch is gonna get replaced, it's acting kinda goofy anyways. I'll let you know the outcome.

01-26-2006, 09:54 AM
I would say you found the problem. let us know how it goes.
It makes you wonder if it was the main problem all along.
Might have saved the trans rebuild .

01-26-2006, 05:03 PM
We have a winner. Ignition switches work wonders.

01-26-2006, 05:48 PM
Thanks for posting back the fix and letting us all know how it went.
Glad you got it going.

01-27-2006, 05:14 PM
I find these people to be very knowledgable

Good Luck My GM Brother:wink:

01-13-2011, 12:34 PM
Our 03' GMC Savana shift indicator was stuck in 2nd, but mechanically shifted fine. This resulted in a no start condition. Replaced the Neutral safety switch, nothing changed. Checked for voltage at the Ign.1 "O" fuse,and the pink wire at the trans. neutral safety switch. All tested good, battery voltage. My Innova scanner did not indicate any trouble codes, but I went ahead and "cleared codes", and before my eyes the shift indicator moved to park and everything is fine, truck starts, shifts, fixed.

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