4L80 in limp-home

schmittygm · February 15, 2007

Hey all. I'm sure some of you have heard about this in the past so i'm asking for your infinate wisdom.

Recently my '95 w/6.5 diesel & 4L80 started acting up on me. Every time I start it up, the trans is stuck in 2nd. But when I cycle the key (turn it off and on again) the trans will shift just fine. I pulled a code #81 on the computer which is 2-3 shift solenoid circuit malfunction. The GM tech around here said it was that solenoid that needed replaced. But as I do more research I find more people saying it could be an ignition switch instead. I guess the ignition switch makes a bad connection sending a fault to the computer which kicks the trans in limp-home mode. And once you re-start it, it is fine. Any of you had any experience with this problem?? Is there any way to test either the solenoid or the Ign switch??? Also, anyone have wiring diagrams or know where to find them??? Any help would be awesome!

thecraft · February 15, 2007

But as I do more research I find more people saying it could be an ignition switch instead. I guess the ignition switch makes a bad connection sending a fault to the computer which kicks the trans in limp-home mode. And once you re-start it, it is fine. Any of you had any experience with this problem??

That's definitely possible, when the ignition switch went out in my truck (a LONG time ago), the tranny wouldn't shift out of 1st.

schmittygm · February 16, 2007

I know, its kind of frustrating. Anyone else have any experience with this??

schmittygm · February 16, 2007

What about wiring diagrams?? is there ANYWHERE on the internet to find them without paying for them???

yeehaw87 · February 16, 2007

In my '96, I had the same problem, it would only stay in 2nd or 3rd, and i had to manually shift, also, it threw solenoid codes. I put a new ignition in, it fixed the problem, but the code is still being thrown. But it runs fine so I don't worry about it. I would start there.

schmittygm · February 17, 2007

Well, sees to me, it doesn't matter which gear its in. I can manually shift it all day and it wont shift out of 2nd.

90GMCZ71 · February 17, 2007

Hi,

I am not a tech just a gear head. I have the factory manuals for 1996. If the ignition switch is bad, the tranny does not get 12.2 volts on the red wire in the transmission harness.

In my 96 manual, red is power and brown is ground. Ignition on, measure the voltage across those two wires at the transmission harness

//90GMCZ71

95Sierra2500 · February 17, 2007

The solenoid is in the transmission, but you should be able to get to the connection at the side. Given how old the truck is, it might be possible to replace the ignition switch and see if it fixes the problem. If not, the solenoid will have to be replaced, and I'm not sure if that involves pulling the trans. The trans does not have to be taken APART, but it may have to be removed for room...again, not sure.

schmittygm · February 17, 2007

You can get to the solenoid without pulling the trans. Pull the pan and its right there. I'm just trying to get away from doing that much work as I do not have a lift or anything. Doing the ignition switch is still quite I job I believe.

1999 Tahoe 4x4 · February 19, 2007

Ignition switch definately CAN cause transmission problems. I already had to change mine at around 70k. In my case the A/C, transfer case, and the ABS were affected. These are THREE circuits Upon opening the switch I found almost all contacts for all other cirvuits burned as well. A wonder that some of those circuits still worked. BTW it appears that the switch is NOT to be serviced. Upon opening expect it to be never to be working again.

You can probe the ignition swich exernally too. I did so. Upon doing that I found out that there was a voltage drop of about 6V at the switch. That is when I decided to change it. The switch costs around $200.-

I can send you the diagramm as an e-mail if you pm-me your e-mail.

yeehaw87 · February 19, 2007

Yeah, its a kick in the nuts to put in the switch if you dont have the right tools too. Theres two torx head screws that I could only get one out. I ended up breaking the other one off. Sucked, but it could have been a lot worse. Any more information on the transmission solenoids would be cool, as too how much they are and how to get them out, I know my computer is throwing two codes for that. It shifts like a champ, but the check engine light bugs the hell outta me.

schmittygm · February 28, 2007

Is the ignition switch that hard to replace...i mean other than the 2 torx screws and having a lot of patience? I'm hoping I can do it myself but i am beginning to get discouraged. Maybe if I can get the diagrams from 1999 Tahoe 4X4 i can figure it out. My e-mail is [email protected]. And..WOW $200 for the switch. I didn't think it would be quite that much. Thanks guys