I have been working at getting the overdrive back since it went south about 10 days ago.

The same day the OD stopped engaging, I changed the trans filter and gasket using a Napa kit, & flushed the system. No metal in pan, 2.5 years since last change, fluid looked bad though. Both trans cooler lines were cracked at the forward oilpan support. so the leak areas were cut out and bridged using HD hose and clamps. No more leaks.

The OD stopped engaging while on the road. Stopped for a stopsign on the highway, OD never engaged again. Trans feels like it wants to make the shift to 4th; it unlocks and the revs elevate, but it never shifts into 4th. There had never been any concerns of the trans "hunting or stalling" its shifts.

Shifting is very smooth from 1-2 at about 17mph, and then from 2-3 at about 27mph.
The Overdrive lock out switch works fine. If engaged, the trans runs at about 250 rpm lower than if the button is not engaged.

I have tested and cleaned the TPS, took it apart. the values change on the ohmeter when moved. The wiring plug reads 5 volts with key on. I took the bolt guides out and tried adjusting the TPS position; no change.

I cleaned the trans temp sensor plug. I disconnected the negative grounds.
I have not looked at the PCM.

There do not seem to be any indications of error codes to salvage, no check engine light, or other dash light stays on. ABS is working fine, I have the 4 wheel ABS.



One Question, am I doing any harm running the truck in 3rd gear?

It is shifting great, just won't engage 4th gear. Your ideas are appreciated greatly!

thanks

Lester

 

The tps also conrols the cruise control,you did not mention if it was working,if not the tps may be shot,can you acheive the proper ohms values when adjusting the tps?also check for grounding at the tps.

 

You say it unlocks the converter in preparation for a shift, and then continues to run that way, unlocked in third? Sounds like the PCM is trying to shift it, so is likely an internal trans problem. OD solenoid maybe, or OD circuit hydraulic circuit leakage?

 

There is a temp sensor in the tranny cooling line....sounds like it when bad....same thing happen to me changed sensor and O/D worked again if I remember it costs about $30 from the dealership

 

The Cruise control does work.

I thought about putting the 1000 ohm resistor across the plug contacts of the temp sensor to see if this will "fool" the PCM into allowing the shift. Dealer is 120 miles away, so not a short jaunt considering an iced up highway.


thanks

lester

 

Happy New Year to all Dieseltruckresourcers!

I got a trans temp sensor at NAPA, part @ TS3001 NAPA Echlin brand. The replacement has a shorter probe than the original. The OD still will not shift! Tested the orig sensor on ohmeter, it gave a steady value @ 12.045

I would sure appreciate knowing more about how to inspect for the OD solenoid or OD circuit hydraulic leakage that Torquefan mentioned.

Thanks for your help on this.