Tranny Limp mode

[Fossilfreefuel]

Hey all,

So my tranny on a 96 6.5 4x4 is only in second gear. Here's what I did so far...

1. clean the grounds on the hitch wiring harness.

2. clean the ground strap from the frame rail to the firewall.

3. swapped the input VSS with the output one that's not used on the 4x4's

4. replaced the rear output VSS on the transfer case.

The ABS light does not come on
The spedo does work
I just got a new ECU at the dealership 3 weeks ago.

Are there any other grounds that I should check and what are their locations?
Are there any more simple things I'm missing?

Thanks in advance!

[JohnC]

What codes are set?

This problem is often caused by bad or no power to the trans solenoids.

[Fossilfreefuel]

Here are some codes we got...



*DTC 81 - 2-3 Shift Solenoid Circuit Fault
*DTC 82 - 1-2 Shift Solenoid Circuit Fault
*DTC 83 - TCC PWM Solenoid Circuit Fault

along with a couple EGR codes that I feel are unrelated.

Any way to check the power to the solenoids? Is is easier to just run new hot leads from the ignition power?

Thanks!

[bcbigfoot]

The trans will go into limp if the trans. fuse blows likely caused by a bad shift solinoid. Change the fuse and take a test drive, the fuse will blow when it shifts into the range with the bad solinoid. Example might be the trans. works good until tcc locks up = bad tcc solinoid.

[Fossilfreefuel]

The trans fuse is not blown.

With the IG on it receives 11+ volts. Cranking receives 9V, and with the vehicle on gets 13V.

Any other things to look at? Could the solenoid still be bad even if the fuse and circuit appear to be good?

[donbfishin]

My 4L80E is also locked in limp mode. All fuses, cables, grounds have been checked and are good, but it only has 2 sensors on a K2500. It has a front & transfer case speed sensoe, but none in the rear of the trans, just a empty hole. Is the K2500 supposed to have 3 speed sensors or only 2 ???It is throwing numerous codes like a bad ground or connection, but all have been cleaned. The codes are 35,39,68,81,83,99 which are TCC lockup, Trans slipping,shift solenoids and TPS, which have not shown any problems b/4 limp mode problem. 95 K2500, 6.5, Sol D, 97 air intake, 3.73 w/ Auburn posi, JK chip & exhaust, Bilstiens, remote 2 qt oil filter, headlite relays, fast idle switch & more. Don

[Fossilfreefuel]

Only 2 speed sensors
on the 2wd the rear sensor is the same as the front one
on the 4wd the rear sensor is present but with no wiring harness, instead the rear is on the transfer case and referred to as an ABS sensor.

[Robyn]

Have we checked battery grounds at the engine and the battery as well as the charging cable to the RH battery.

Battery cable issue raise havoc on these trucks when the power levels start dropping off.
For example if the RH battery ground is good and the left one is crap the truck will usually run but all sorts of wierd crap can happen.

Check these real good and make sure you have good power level when the rig is running.

14.2-14.7 at both batteries as well as the main power buss on the juction block.

If these are good and the gounds are ok then you can rule out power at least at that point in the system.

A scan with an tech tool may be in order to narrow it some.

[Fossilfreefuel]

I recently moved the grounds from aluminum air intake to spots on the block. I think one is on the rear of the rear of the power steering pump mount and the other on the A/C compressor mount.

I was advised to move them because having a ground going through aluminum to steel causes electrolysis.

Is there any way to test grounds other then an ohm meter? Also, the truck shifted fine for a week or so.

[Fossilfreefuel]

The junction box under the hood and both batteries were at 14.5 steady at idle.
Does anyone know which harness on tranny is to the shift solenoid? There is the round one and then two on the actual shift mechanism coming from the cab.

[gmctd]

Multiple DTC's and limp is usually indicative of connector problems - R&R the large connector on the driver's-side, inspecting the contacts while it's unplugged for dirty\oxidized\corroded pins, also frayed wiring.

Trans will go limp if system voltage is low, which includes bad grounding in harness\connectors - will also go limp if engine is limp, caused by any of several critical engine DTC's - very important to read and note all DTC's B4 clearing them, then noting any that reoccur after clearing

Trans slip is usually one of the speed sensors, also dirty\oxidized\corroded\frayed wiring\connectors - 2wd uses the two on the trans, 4wd uses the front one on the trans, another on the transfer case - the rear one on the 4wd trans is unused, may be exchanged with the front one for test - later models may have a blank plug there.

Both posts indicate internal solenoid DTC's - I'd suspect harness problems B4 going into the trans, but both could need service

[donbfishin]

Thanks for the suggestions.. Main harness plug was cleaned & had dielectric grease added, no change... Trans pan is coming off today & 3 new solenoids being installed, then back to the drawing board (test drive time). Wish me luck.
Don

[gmctd]

Just re-read thru this again - 11volts is not suitable with IGN on, not running - something is dropping the voltage to the fuse, may be the problematical IGN switch, itself - should read battery voltage, even in crank mode, as the starter is hard-wired to the batteries, not the IGN system - may be the battery(s), but faulty connections give same results as faulty devices.

BTW and FYI - replace both batteries together, simultaneously, in tandem, in pairs, a couple at a time, 1+1, 0+2, L + R, passenger-side + driver's-side, port + starboard, absence makes the heart grow fonder, ya can't have one without the other, don't leave home without it, with a knick-knack paddy whack give the dog TWO bones, can ya hear me now...............

[Fossilfreefuel]

So I'm getting 13 V to the fuse with the vehicle on.
I tried hooking up a 12V direct from the bat. to the fuse and was getting 13.6V w/ headlights on and 14 w/ headlights off. This didn't seem to make a difference in shifting.

I also noticed that if the trans is not getting power at the fuse the shifter light does not come on (a good way to tell if there isn't power to the trans.)

I assume that the fuse labeled 'trans' inside the fuse panel in the cab is the one that controls the tranny.

I just replaced both batteries a month ago and redid the end connections. I'm getting 14.2V at idle.

Anymore help is appreciated,
Dave

[Fossilfreefuel]

I got a scanner and am consistently getting the same codes-

Speed sensor input circuit
torque conv. quad module
shift solenoid A circuit
shift solenoid B circuit

My thoughts are back to electric problems.

[Fossilfreefuel]

I fixed the problem. After confirming the shift solenoid harness was getting 12+V consistently we found the ground. The ground toned the multimeter but when looking at the actual ohm resistance it was getting 47. We scotch locked a ground then connected it direct to the frame rail. Low and behold it shifts. Now the ohms reads about 7.

Thanks for everyone's input. It would help if the ground and power wires location and colors where known.