97 Legacy outback wagon -Code P0740 after head gasket repair..Help Please!!

[shiner51]

I have a 97 Legacy Outback wagon 2.5 that just had the head gaskets replaced. The engine now runs fine ..no more overheating problem. However on the first trial run with the new head gaskets, my mechanic got code P0740, Torque converter clutch circuit malfunction, and the transmission will not shift into overdrive(or the final drive gear). There are no other shift issues and the there has been no previous transmission problems, which leads me to believe that it is a wiring issue external to the transmission, that was either overlooked or caused when the engine was put back in the car. Im thinking a ground or short somewhere. My mechanic says he has double checked all the plug ins and they are reconnected and secure. Has anybody here had this problem before? Will it hurt to drive the car in 3rd gear while we are trying to figure this out? My mechanic is a really good motor guy but not a transmission guy, and this is his first Subaru. Any help is greatly appreciated.

[OB99W]

[...] my mechanic got code P0740, Torque converter clutch circuit malfunction, and the transmission will not shift into overdrive(or the final drive gear). [...]

 

The definition for P0740 in the '97 factory SM is "Torque converter clutch system malfunction", which can have several causes, only one of which is a problem with duty solenoid B or related wiring. Problems in the following circuits can also trip that code -- throttle position sensor, vehicle speed sensor 1 or 2, engine speed input, inhibitor switch, brake light switch.

 

Assuming no external wiring problems, sometimes there is internal damage if the trans was jacked at the pan -- it takes very little deflection to cause trouble. Check the pan for even a slight deformation.

 

Otherwise, check the other circuits.

[shiner51]

Thanks OB99W! Will get right on it and post the results.

[shiner51]

While my mechanic is trying to figure this out, will it hurt to drive the car in 3rd gear?

[interceptor]

Any resolution to your problem. I have the exact same situation. Head Gaskets repair (did it myself) and all is well now except for TCC Lockup issue. Any insight is greatly appreciated.

[bstone]

Check not only the plug ins but the wires themselves. I've seen crazy cases where one wire is stripped/cut in the middle but either end is as it should be.

[interceptor]

Thanks bstone. I've checked every connection but I haven't traced all the wires yet. I've seen posts of possible damages inside the pan from jacking the tranny up, which is possible. I thought I spread the weight across a wide enough area of the pan to avoid such an issue, but probably not.

[interceptor]

Thanks everyone for your input. These forums prove invaluable for diy'ers like us. I dropped my pan and found a pinched and broken blue wire (duty solenoid I think. Repaired the connection and I'm resealing the pan now. Putty knife was easiest way to separate the Pan. Permatex Ultra Grey for the gasket. I'll post the results in a couple weeks to see if the fix lasts. Just shows to be careful and make sure you jack up your tranny carefully and disperse the weight...or get a tranny jack. Cheers!