6.5TD Codes / Not shifting

[NickTransmissions]

Also adding that I didn’t clear codes today but the day this started I did reset it so all codes are pretty fresh from just a few short drives

What gear is it in when you put it into drive?

Codes 28 and 59 are the pressure switch manifold assembly, a small electronic part bolted to the valve body. Its job is to tell the PCM what gear the transmission is currently in and what the fluid temp is by monitoring for pressure within the various hydraulic apply circuits and streaming temp readings to the pcm.

So if its bad, youll be in limp mode and have only reverse and second gear. Line pressure defaults to max when in limp.

Here's the part in question - its the oblong shaped object with six bolts going through it.

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[pnwestern]

Thank you @NickTransmissions
Unsure on which gear its in but 2nd sounds about right. Tried digging into information about testing the switch but did not find much info so I assume the recommendation is to just replace it and say a lil' prayer

 

[NickTransmissions]

Thank you @NickTransmissions
Unsure on which gear its in but 2nd sounds about right. Tried digging into information about testing the switch but did not find much info so I assume the recommendation is to just replace it and say a lil' prayer

You're welcome...Yes, replace that switch, it's done.

While you're at it, replace the filter (if not already recently swapped), two shift solenoids and wiring harness as the harness likes to leak through the connector when it ages and I've seen cases where that leakage causes the trans to go into limp mode. Shift solenoids have a tendency to come apart in your hands after so many miles therefore it's best practice to replace when as well doing a 100k service. Ohm out the electronic pressure control solenoid (large cylinder-shaped object) with a multi-meter to make sure it's putting out it's usual 4-5.5 ohms...if not, replace it as well.

You DO NOT have to drop the valve body to replace anything mentioned above.

 

[pnwestern]

Found time today and replaced all shift solenoids, pressure switch, pressure solenoid, and filter/fluids. Wasn’t able to replace harness as I have the center T25 screw and that harness seems to be NLA. Still have the same issue. Any thoughts?

 

[NickTransmissions]

Found time today and replaced all shift solenoids, pressure switch, pressure solenoid, and filter/fluids. Wasn’t able to replace harness as I have the center T25 screw and that harness seems to be NLA. Still have the same issue. Any thoughts?

You also have other codes that may be contributing to the problem. Code 85 is a PCM prom chip error/failure and code 87 indicates gear ratio error. Check your speed sensors with a multimeter for function using the low voltage setting on the meter.

Unplug the speed sensor harness, chock the front wheels, put the truck in neutral, get the rear wheels off the ground and spin them while you you place your meter's test leads on the rear speed sensor's male connector tabs. You should see voltage increase as you spin the wheels. You will have to get the input shaft turning to test the front speed sensor in the same manner. Alternatively, if your rear speed sensor tests good and speedometer works, switch the speed sensors - put the rear speed sensor in front and vise versa. If your speedo no longer works you know the currently installed front speed sensor is bad. Buy an AC Delco replacement, if so.

You also mentioned previously that reverse felt "tight" as if the parking brake was on - is that still the case?

 

[pnwestern]

Well, I ended up folding and took it to a transmission shop where they recommended an overhaul. Price was $7700 for that and said a new transmission was even more which seems a little wild. So.. I think I’ll buy one myself (seeing 2-3k) and get it done but will have 2-3 questions once I narrow potentials down.

Here is their input, thoughts welcome

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[pnwestern]

@NickTransmissions to answer your last q it was the same (tight reverse) but realized that was only when cold. Seemed it needed to build pressure or warm a little first

 

[pnwestern]

Well to close the loop I found a local guy to rebuild at a good price. Now has the TransGo HD2 shift kit which is nice although 2nd gear is little abrupt; enough to notice but not worry about

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And just like that we’re back on the road. Picked up rail caps, a bed box and have tires going on this Friday. Maybe I should start a new thread..

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