Cruz;Brake;Tranz issues

[Daver94K2500]

I am having intermittant issues with the cruise control, RWAL brake functions and the transmission lock-up at highway speeds. I have noticed that on long trips several hundred miles the cruise control just drops after attempting to climb a long hill usually pulling a light trailer; <5000#, then I notice that the transmission does not lock the torque converter, and the brake warning indicator lights. The cruise will not re-engage until I cycle the ignition key off and on again or stop the vehicle. The speedometer never ceases to work during this leading me to belive that the VSS is still working although I understand that these are all tied together. After restart, the cruise will resume working until the next steep hill attempt and the system will fail and remain disabled until the next restart. If I continue driving after the cruise fails, the brake warning indicator will eventually start flashing code 9. In some cases, I have had to stop the vehicle, turn off the engine, remove the fuse to the brake system, reinsert and restart the vehicle to make things work again. These circumstances are not associated with hard braking events and the isolation dump valve has been replaced. I have good brake operation and feel occasional pulsations of the RWAL when stopping on loose gravel roads. The transmission is functioning normally outside of the log trips and the cruise failures. It is a 94 K2500 with 257,000 miles. Any suggestions?

[GMC Hauler]

Check your ground on your intake manifold, rear passenger side. I once had intermittent ABS, Brake failure lights, which ended up being that ground.

Welcome to The Diesel Page. :D

[damork]

Dave,

GMC Hauler is right, and follow the passenger side ground on the engine down to the frame connection near where the turbo down pipe passes by. You might find the ground loose there or even broke. Also look back where the white wire from the trailer wiring harness grounds to the frame - it was on the drivers side of the frame near where the receiver attaches to the frame on mine. Also, there was a ground wire coming out of the fuel tank wires that connects to one of the cross members on mine - it was nearly broke off from corrosion.

[BobND]

There was a post a short while back about dirt, moisture, and corrosion in the trailer brake connector causing all sorts of problems from other circuits feeding voltage into the brake light circuit and confusing the computer, and the problems you're having COULD all relate to circuits controlled by the brake pedal switch.

In addition to the actual trailer brake socket, there could be similar corrosion and moisture in the adapter that plugs into the taillight circuit to feed the trailer connector (if so equpped).

[TJ Moose]

I've experienced cruise control cut out on long climbs, and I attribute it to 2 things - well may be 3. The first was that at the time, I was an unknowing diesel spec, floating through the cosmos - unaware of the great body of knowledge contained in the mother ship known as "The Diesel Page" - meaning - I wasn't being particularly nice to my 'Burb (1995 6.5TD)in how I drove or maintained it.
Second thing - I think cruise control cut out on some grades, just because computer was registering too much heat, and just pulled the plug on the throttle. At the top of the hill, when heat and load went back down, all was well.
Third instance - in a very long run with my trail Jeep (2+ tons of wheelin'fury) on a trailer up Cabbage Hill in eastern Oregon I-84 - cruise control gave it up and didn't come back - and the tranny went to 2 gear and would not shift out of it, even when hitting the flat on top of the grade. It would shift again after pulling over and letting things cool - but would go back to 2nd as soon as things heated up. Seems there are speed sensors on both the tranny and transfer case (if you have 4WD - I do) and I may have fried them - as they have something to say to the computer both about cruise control and tranny shifting. Shop I took it to after a weekend of cooling could not duplicate tranny problem, but cruise was not working - yet they did not pick up error codes. Changed both sensors out, replaced the burned transmission fluid (I wonder what it takes to burn Red Line synthetic - another pre-TDP oops) and all has been well ever since. Good Luck on the search.