Guntar13

I have a 98 sport 4.0 auto that I'm currently toying with. Problem I'm having is the torque converter doesn't lock up. I have all the gears and it winds out a little far before shifting (about 2200). When i get to highway speed i have no lock up. I have verified this by testing for lock up and using my snap on scanner to watch if the converter locks and it doesn't. The MIL lamp comes on after awhile with P0740 which is converter solenoid malfunction. I went ahead and dropped the pan and filter and put in new to me solenoids (all of them). these also came from a 98 that was shifting great but blew the engine. I reset the brake switch, checked the detent cable. New fluid and filter. It had this same code before i put the solenoids in which leads me to believe it is not actually in the solenoids. Getting a little frustrated and lost on this one. I don't know if this would be related but the cruise doesn't work also. The on/off switch does work and indicates the cruise is on but you can never "set" it. No matter what speed you are the cruise won't set. Any help is greatly appreciated. Thanks

CCKen

I don't know what you mean by "reset the brake switch" but a defective brake lamp switch would cause both the lock up and crusie problems.

Cheap fix. Replace it.

Guntar13

I mean set it, you know pull it all the way out and ease it back till the plunger sets. Wouldn't a faulty switch make the lights not work also? Or could it be that it's dead on one side?

CCKen

There are three sets of contacts in the switch. One set (terminals 1 & 2 are for the brake sensor circuit (TCC & Shift Lock Solenoid), one set for the stop lamp circuit (terminals 5 & 6), and one set for the speed control circuit (terminals 3 & 4.

The switch cannot be adjusted after its initial installation. The plunger ratchets in to place at initial install and cannot be repositioned.

The contacts in the switch do go bad over time and the only fix is to replace it.

Guntar13

Grabbed one to try (6 dollars you can't lose). Just so my mind is right the ground for the tcu is on the oil dipstick stud right?

Guntar13

Brake switch was no help. Cruise works again ( wiring at cruise servo wasn't seated all the way) back to the drawing board I suppose. Grabbed a Known good tcu gonna throw it in and try

CCKen

No, that ground if for the Data Link Connector.

The TCM ground is at the ignition coil mount bracket studs.

CCKen

Good idea. Let us kinow how that works.

Guntar13

I did make sure all those grounds were cleaned up, the tcu i got was from a 98 also but it was late production so the harness was a little different. No go there

Guntar13

Sat down and started thinking, okay i can clear the code and go drive around for 15 minutes or so, sometimes have to make a few stops and then it pops back on. P0740. If it was a short i think the check engine light would immediately pop on?
So that leads me to possible mechanical problems? I wonder if i hook up a switch to manually lock the converter and it works then not sure where i would sit then?

CCKen

What's different about the harness?

You should have a 56041386AA TCM in a '98.

In "99 (to '01) they switched to 56041386AB, but I don't think there's any difference between the two.

CCKen

The first thing in the diagnostics manual to check is the trans fluid level.

Is it full?

Is it black (dipstick check), does it smell burnt?

Are you using Dexron III/Mercon fluid?

CCKen

You are correct.

Generally, with transmission faults if the code sets on start up, it's an electrical failure. If the code sets only after driving the vehicle it indicates that the TCM has tried to do something and the results are not happening, i.e., a mechanical fault. For example: The TCM commands Solenoid C to activate and the TC doesn't lock up.

There are cases where solenoids are stuck open or stuck closed and cannot respond no matter what signal was sent. Same goes for reading resistance of a solenoid; it could read out at 11-15 Ohms but the valve is stuck.

The valve body could be a mechanical fault as well.

You must have full, clean, and proper ATF before the trans will operate to spec.

Guntar13

fluid level is perfect, filter and fluid changed yesterday when new used solenoids were put in

Guntar13

What are the thoughts in running something like trans x through it for a while? The only reason I say that is because the jeep sat for more than a year not doing anything until I got it running. So my school of thought is that maybe it's just all gummed up still and something needs broken free? There wasn't much debris in the bottom of the pan and all the gears are working right