Engine/Transmission (1998.5 - 2002) Transmission not staying in overdrive

[SRutledge]

I have a 2001 3500 350K on the engine 200K on the Jasper transmission. Have dealt with the usual TC lock/unlock issues usually fixed by cleaning batt terminals. But now it shifts normally until it reaches final gear, unlocks and from there it is hit or miss on when it will lockup and go into OD. It stays unlocked more than locked even w/ OD turned off. Going out to load test batteries now and check voltage at APPS

this morning. Has anyone solved any issues by replacing battery cables( I noticed corrosion starting to creep up into the cables).

SRutledge

 

[HBarlow]

Are you sure the transmission is not shifting into overdrive range or is it failing to lock the torque converter?

 

[SRutledge]

It is shifting into overdrive and locking up but as soon as it makes its final shift it will start unlocking/downshifting and will stay in what I will call 3rd gear unlocked under heavy trottle. If i go to light throttle/ not heavy pull it will start "hunting". This hunting is a more extreme version than what i have experienced in the past.

 

[cerberusiam]

When was the last time you serviced the trans and changed out the gov solenoid and transdcuer?

Corrosion inside the cables will cause all manner of electrical gliches if it is bad enough. You might want to try the mystery switch on the lockup circuit to validate whether it is a mechanical issue or an electrical issue.

 

[SRutledge]

Trans is due now(25000 miles). Gov solenoid and transducer has never been changed.
I thought about the mystery switch. Could you point me in the right direction on how to install.

 

[cerberusiam]

IIRC, pin #7 on the trans control harness is the TC lockup sense circuit. The pin numbers are on the inside of the truck side plug. Manually locking the TC should stack shift the transmission into OD and it should stay there. If it doesn't you have a mechanical problem in the transmission. You need about 6 ft of 18 gauge wire, a single throw switch, and a 1/2 watt 33 ohm resistor. Scotch lock the wire to the pin #7 wire and run to the switch, wire the resistor between the other side of the switch and a ground.

I would try the mystery switch first to see if it is mechanical or electrical. If the switch will hold OD and lockup then I would swap out the transdcuer and gov solenoid probably the output shaft speed senor and see if that makes a difference.

 

[SRutledge]

Is this wire on the engine side plug at the pcm. What color is it? Want to make sure I get the right wire

 

[cerberusiam]

Yes, on the engine or truck side right at the transmission plug. The wire colors are differennt for different years so that doesn't always cross over. Some are black with an orange stripe, some black with purple stripe. Best way to do it is look at the inside of the plug and fine the numbers by each pin to verify which circuit. If you have an FSM that should tell you and I don't have one for that year.

 

[SRutledge]

Mystery switch installed and everything stays in w/ no slipping. Changed fluid, filter, gov solenoid, and transducer, still unlocking and dropping into 3rd.

 

[cerberusiam]

Now you are into what is causing it to drop both OD and lockup electrically. The could be in the ECM, the PCM, harness noise from Alternator or battery ground, bad connections or bad grounds.

Without a scope it is hard to find the noise signal. Without a Dodge scanner for that year it is impossible to tell if it is demanding lockup and OD or not.

 

[SRutledge]

Yeah, got a close friend who has a son-in law that works at a Dodge dealer. He is calling him as of right now. I'll keep you posted.

 

[SRutledge]

Sorry about not keeping everybody posted, been a rough month. Ended up replacing batteries, starter, gov sol and transducer. Still had to use mystery switch most of the time. One day the truck went into what I will call limp mode(stayed in 2nd gear) for about two seconds in the morning and about 30 sec 3 hrs later. After each episode the trans shifted and stayed locked like it was brand new. Only happened one day . Next day, back to using mystey switch. Batteries and starter were replaced a couple of days later(cracked - post on drivers side battery and weak starter).
Starts great but i now have my unlock issue even with the mystery switch on. Scary feeling when trans drops into 3rd at 65 mph.

 

[SRutledge]

Finally dawned on me that my mystery switch started having a mind of its on the afternoon after i changed out the trans speed sensor again(code in ECM P0731 if I remember right). Put speed sensor that threw code back in and drove ten miles without having to use switch. Trip to Atlanta tomorrow will let you know how it goes.

 

[Misenheimer]

What is the problem with using the scotch lock on the wire at the PCM?? Out of the road grit and corrosion??

Just asking.
Thanks

 

[SRutledge]

Don't see where that would be a problem as long as you know your on the right wire.

 

[SRutledge]

Took my 3 hr round trip to Atlanta today shifted fine without using mystery switch. Got 20 miles from home and truck went into limp mode and trew code P0720. Changed OSS still went into limp mode at 15-20 MPH. Made it home. Any help on schematics and voltage specs for the Output Speed Sensor would help alot.

 

[SRutledge]

FOUND IT!!! Broken ground inside insulation at plug to OSS. 4 hr round trip todat and shifted like brand new. No unlocking and dropping to 3rd. BTW i am calling limp mode 20MPH/2000RPM Maximum