4L80E lost 4th gear

[Captkaos]

I was driving my Crew Cab and in the past it has been workiing fine.  The last time I drove it I made it about 15 miles from my house and went to pass someone and it kicked down to 3rd and it never shifted back into 4th.  I haven't driven it again, but I plan to test it tomorrow.  Anything I should check first?  I really don't want to drop the valvebody, but I don't want to drive it without 4th.

[Irish_Alley]

capt heres my thing if you vile Sgt blazin ask a question on here I'm not going to even try to respond or help out cause you four usually help me out when I'm wrong lol sorry no help this time

[choptop]

Ive got a good friend thats a trans expert. I'll get with him later today, and see what advice he has.

[Captkaos]

I plan to check everything today short of pulling the pan, then do some musical trucks and get it where I can take it apart without blocking everything.

[VileZambonie]

There's an updated 3/4 clutch but what is it doing? Not shifting out of 3rd or slipping in 4th? Did you scan it yet?

[Captkaos]

shifting fine other than not shifting to 4th.  No slipping at all.  Truck only has 165K on it.
I haven't scanned it yet as the software I have WINALDL won't scan that model ECM.  I downloaded TunerProRT and Hope to try it today if it will scan it.

[VileZambonie]

Let us know. If solenoid B is malfunctioning or the 2-3 shift valve is stuck it won't upshift into 4th

[Captkaos]

Will do.  Waiting for the Dish mover guy to show up...

[Lt.Del]

the only thing i can add is that my 4l80e was messin up about a year ago and found out one of the VSS had the wires stripped and throwing bad info to the ecm.

There was one other occasion when the trans did what you said.  It wouldn't go into high gear.  I didn't think much of it.  When i got home, I unhooked the battery to try and reset the computer.  I dont know if that did something or not, but she has been fine ever since. i have 210k on mine and still runnin strong.

[Captkaos]

I scanned it with a buddies Tech 1.  Solenoids are all working for the 1-2-3-4 shift.
I didn't drive it for 2 weeks and when I drove it it didn't act up, when I drove it in to get his scanner it was fine that day also.  Later that day it sounded like it was locking/unlocking the TCCl but I couldn't check the scanner as it slid across the truck seat..

I have a 68 and 83 code in it now.

I drove it today and it has a current 68.  It seems to only happen under a load. 

Ideas?

[VileZambonie]

The first thing I would check is your tcc brake switch and the harness connections/wiring. From there follow this diagnostic strategy






Circuit Description:
The PCM/TCM continually monitors voltage on each circuit connected to the "quad-driver" for either low or high voltage, depending on the commanded state of the device connected to it. Code 83 will set if the PCM/TCM detects an inappropriate reading on the TCC circuit. For example, if the TCC duty cycle is 0, but voltage on the TCC circuit drops as if the solenoid were applied then Code 83 will set. The TCC solenoid, because of it's large current draw, is connected to two terminals of a single "quad-driver."


.


Test Description:
Number(s) below refer to circled number(s) on the diagnostic chart.



This test checks for low resistance in the solenoid or internal transmission harness. The test also determines which circuit triggered the fault.
Diagnostic Aids:
Be sure to check all connections, especially those at the transmission pass-thru connector.

[Captkaos]

Just getting back to this but code 68 is intermittent.  So what is the "Diagnostic aids"

[VileZambonie]

Basically the first things I posted there. Check the brake switch, the connector, wiring, pin tension, unwanted voltage drops etc.

[Captkaos]

I couldn't find any thing out of the norm, but I am still looking.