Any ideas??? While cruising anywhere from 45-65 mph the torque converter will unlock and lock back up erratically. This doesn't happen all the time. First time this happened was a few weeks ago and didn't happen once we were trailering a car home. Then did it again a few nights ago. Seems like while it's cruising. No OD light flashing.

 

If the brake lights turn on the TCC will disengage. The brake switch could be faulty.

 

Could be but I doubt that. I thought of that and figured since the cruise doesn't disengage when this is happening I ruled that out.

 

The brake lights and the CC disconnect do not share the same set of contacts on the switch.

 

I had a similar thing, turned out to be a bad coil. Apparently the lack of power made the trans unsure where to go when under slight load in the 45 mph range.

 

Try unplugging the TPS and put an analog ohm meter on it and see if the needle swings smoothly as you exercise the throttle. The TPS may be worn right where it spends most of its time and if it has a few jerky spots right there, it might be confusing the PCM as to wheather it should lock or unlock the TC.

 

Yes, the brake lamp circuit is separate from the signalling half of the switch. However, the half of the switch is used for all signalling of the brake pedal position does control the CC and the TCC. It might be the BPP switch... or it may not.

If you have a scanner what can log live data in Mode 6, you can watch the various inputs and outputs of the PCM to see if the unlock/lock is commanded or not. If it's commanded, you can look at the various sensor inputs to see if you can catch the glitch that's causing the symptom.

 

I talked with a transmission guy and he said to check brake light bulbs and the TPS. He said the same as you pdqford about it wearing in one spot. I will have to get an analog volt meter since digital would work so well. He also told me about a product called Dr. Tranny Shutter fix. Anyone use it before. He said he never recommends additives to transmissions with the exception of this one. He has had excellent results and customers are happy it saved hundreds of dollars. Thanks for the advice so far.

 

I wasn't a big additive guy either but after my tranny started shuttering between 3rd and OD, I added Slick 50 initially and when I couldn't find that any longer, I started using Lucas Tranny additive when changing fluid and filter.
As I've said before in other posts... 300k later and some aggressive towing, a 10k toy trailer and a 25' powerboat, she's still going strong.
I have however, moved to an F-250 6.0L diesel for my towing now with a bigger 15.5k toy trailer.

 

Checking the brake lights on this truck won't matter, but checking the TPS is certainly a good idea.

I've used the Dr Tranny Shutter Fix before to extend the life of a limping transmission. If your problem is worn clutches or slightly leaking seals, it can help a bit.

 

Might be redunant but can you explain more what the trucks doing to make you say that the TC is erratic?

 

This is an intermittent issue. It doesn't do it most of the time and it started just recently. While cruising(55-60MPH) the TC will unlock, rpm jumps a few hundred, then it will lock in again. It will do this for a few miles, I came to a stop then it didn't do it. Most of my trips with it are short with stops. I haven't had it on the highway for an extended period of time to know whether it would correct itself or keep doing it. I am thinking that the TPS could be a possibility. The brake switch maybe since the roads weren't smooth. I don't have an analog volt meter to test so will have to l borrow one. I doubt a coil pack is the issue as there is no change in power, hesitation or stumbling, etc noticed. A brake switch is cheap and easy to replace so I may do it just to rule it out.

 

Keep us posted with the out come. Theres so many common problems on this vehicle with a million different solutions. I'm picking through a flashing O/D light issue right now.

 

Took it for a little drive tonight to try and duplicate it and I was able to. I have this neat little tool called Scan Gauge II in my Expy. Well, I set one of the readings to TPS so I could see if there was a number that would trigger it. Well, there was. So this is leading me to believe it maybe the TPS sensor after all. Under normal driving at about 57-60mph the gauge was reading 26-28. When I would crest a hill or terrain the number would start to drop and when it would get to the number 21 it would unlock the TC. So I was able to mess with the throttle while cruising and it would only unlock when the number would read 21. Then lock up as the number would increase back up to 26-28. Complete off throttle number was 19. So, TPS??? What do you all think.

 

$30-$50 for the TPS, seems to be a common problem. Cant hurt much more than the ol'wallet. Still can try to hook up the analog vm and see what happens.