Hey all, I've been fighting a P0740 code for months now. New brake switch, mopar tps, new fluid, filter, etc. Replaced all the solenoids as well. Yet it still very much intermittently loses its ability to lock up at speed. One moment it's behaving fine, then you accelerate to pass, and lockup is no longer there. 3k rpm on the freeway. This is becoming very frustrating. It doesn't seem to matter what I'm doing, any change in speed kills the lockup, they you'll be lucky if maybe twenty minutes later it's magically functional again. Rarely. Running out of ideas... I've been searching but nobody seems to have a situation like mine...

 

To lock the Torque converter:
The TCU reads the throttle position and road speed. If it determines you are holding a steady speed above 40-ish MPH AND the brake pedal is not depressed, the #3 solenoid is operated.
That directs hydraulic pressure to the lockup relay valve in the valve body, which in turn directs pressure to the torque converter clutch piston, which clamps the clutch against the turbine hub and locks the converter.
Sooooo... if it isn't locking, it could be the TPS, Trans speed sensor, transmission line pressure, a failing #3 solenoid, a sticky lockup relay or a failing clutch assembly.

Since you changed the TPS and the solenoid with no results, the next thing I'd try is to adjust the TV valve cable to set the line pressure.
If that fails, backprobe the #3 solenoid connector (at the TCU) with a meter, take a drive and see if it's trying to lock the converter. If it is, the sensors and TCU are good and the problem is the solenoid or something downstream from there.

 

Tv cable has been adjusted. Don't really have the equipment to back probe the wire... What do you use? I have a multimeter and such.

 

Here are some TCM inputs test procedures for the '97-'01 AW4. Read the pin outs and procedures carefully before beginning.


Use a digital multimeter.


Use safety pins to back probe and to insert in the TCM pin cavities for the tests. See pic.


Safety Pin probe. Use one that will fit.





TCM pinout:





Procedures:





Example of connector back probe using safety pins:





Example of probing connector pin cavities using safety pins:

 

I probably don't sound like the brightest person asking such a simple question but I wanted to be hundred percent sure before I start stabbing things . Thank you very much for both the tutorial and the example photos

 

I worked on cars for a long long time, but never really dealt with modern vehicle electrical issues like this.

 

Finally was able to perform all the tests. The solenoids all checked out , all voltages were correct except the reverse was a volt low I assume from reverse light load. the real kicker is the speed sensors, I couldn't nail down a resistance value for either one of them no matter which range I clicked on my multimeter. my speedometer does work though.

 

I suggest you stay with trying to get the ISS and, especially the OSS resistance.


Set your [manual ranging digital] meter to 200 Ohms.

 

I tried multiple times. With the battery disconnected I could never get any reading whatsoever it displayed similarly to an open circuit. the only time I ever got a response was battery connected key on and it was 240 ohms fluctuating

 

Is this with the ISS and the OSS?


Maybe there's a wiring fault.


The pic shows the connector that the ISS/OSS wiring goes through.


You may want to check the wiring from the connector down to the transmission for chafing.

 

Thank you!! I'll check asap