95 4L80E

[farmerherb]

Need help quick. Trans. won't shift into 4th. Will shift to 3rd and converter lockup. Thats it. Then when you come to a stop it won't go back to first unless I turn off the truck then start again, then it shift up to 3rd. Just changed the filter and fluid 5000 miles ago always use Amsoil fluid. I thought maybe the 3-4 solenoid is not working, but can't explain not going back to first. Help Please! Checked codes have 34,39,68,87 can't find what 39 or 87 mean.

[JohnC]

34 is an injection pump code.

39 is a lockup problem, TCC stuck off.
68 is trans slipping.
87 is high ratio error, may mean it tried 4th but didn't like the results. Probably related to 68.

[Phil Holmen]

My truck did the same thing and with similar codes if I recall correctly shortly after installing my remote starter, turned out that the second ignition wire wasn't making a solid connection after moving everything around. Don't recall the color but if needed I will take a look for ya...

[farmerherb]

Thanks for the code info. Is there a 4L80 web-chat site than I might get some troubleshooting help?

[JohnC]

I did a little more checking. When troubleshooting it is recommended to start with the low number and work up. Both the lower numbers are specific to TCC problems, so I'm betting that you have a TCC problem. Next step is porbably to drive with a Tech 2 connected and find out what's really happening.

[farmerherb]

Phil if you could remember or look that would be a big help. I have a SnapOn 2500 scanner which really didn't help a great deal, other than the computer thinks everything is working okay. It said I was in 4th gear when I know is was not(RPMs too high). I took it to a 1st class trans. shop(this guy rebuild torque converters in the shop) He put the newest scanner model to work it gave the same info(1-2, 2-3 shift solenoids error, but it also showed problem with the shift position sensor(don't remember real name) The shop owner/rebuilder believes there is a problem with computer. This problem happened once before, I had used the four wheel drive one night in the morning it wouldn't shift out of 3rd. I let it set 2-3 hours started it again and all was well for 2 months. He also said that a poor ground could be at fault. Trans. fluid temp. was 144-161 during a 1 hour drive so that is one reason I believe its electical fault.

[JohnC]

Attach a volt meter to the trans fuse circuit and go for a drive. If the power to that circuit is the least bit flakey the trans will act up. Once it detects a fault it sets iself in "limp" mode which either locks out 4th or locks in 2nd. Cycling the key can reset it. The problem usually ends up being the trans contacts in the ignition switch.

[rjwest]

May be of some help.

http://www.atraonline.com/manuals/general/tetdv/tetdv-toc.htm

[farmerherb]

John, are we talking about the ignition switch in the column? And would you suggest replacing the switch?

[patrick m.]

being a 95 model YES replace the ign switch.
not too hard a job. its right behind the key cyl.

you will need a "deep well" inverted torx socket.
you can get them at any parts house that sells "Lisle" (spell) tools. It is labled "GM ignition switch socket" ;)
The harness that is made onto the switch runs down the column and bolts to the truck connector (either 7mm or 8mm )

[farmerherb]

I just ran a check on pricing the ignition switch. 148.00 from autozone,150.00 from the dealer. Can I clean the contacts if that is the problem?

[DeezlStinson]

I had this problem several years ago.

It turned out to be a poor connection in the battery terminals.

This vehicle is VERY sensitive to electrical problems in general. I also had some of the other codes that were caused by poor connections in the 15 pin plug on the back of the engine.


Cheers,

Rick



Originally posted by farmerherb:
Need help quick. Trans. won't shift into 4th. Will shift to 3rd and converter lockup. Thats it. Then when you come to a stop it won't go back to first unless I turn off the truck then start again, then it shift up to 3rd. Just changed the filter and fluid 5000 miles ago always use Amsoil fluid. I thought maybe the 3-4 solenoid is not working, but can't explain not going back to first. Help Please! Checked codes have 34,39,68,87 can't find what 39 or 87 mean.

[JohnC]

Originally posted by farmerherb:
John, are we talking about the ignition switch in the column? Yes


And would you suggest replacing the switch? [/QB]Only if it checks bad.