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torque converter lockup

0

00XJmike

NAXJA Forum User
Location
Puerto Rico
2000 Jeep XJ, AT, 90000 mi, 3.5" RE lift

I know this issue has been discussed in previous threads but I have still been unable to resolve my problem.

I am throwing a 740 code(tcc lockup). I have replaced the solenoid and am getting proper resistance at all three solenoids, at the solenoids themselves and at the tcu plugin. I have replaced fluid and filter, fluid looks good.

Everything else works fine. Tranny shifts good when accellerating, 1-2-3-4, just no rpm drop for the tc lockup. Gas mileage is lousy, more than usual.
Probably unrelated but I found it odd that this code showed up the day after I did the 1" transfer case drop.
Any help/thoughts appreciated

mike
 
I'm assuming you've already tried removing the TC drop to see if it corrects the problem?
 
igotan, why do you say bad torque converter? know of any way to confirm before I go replacing it? would like to be sure.

dave, i have a hard time believing it is related to the transfer case drop, it is a pretty common procedure and I've never heard of anyone else having this problem due to a tc drop. the tc drop allows for a closer to factory driveline angle due to the 3" lift, it relieves the extra stress caused by the lift.

I still drive it everyday, just doesnt feel like the torque converter is locking up. Its about 2500 rpm at 65 mph, factory gears and 31"tires.
I am considering doing the manual bypass for the torque converter lockup to see if that helps, but I believe I will still be throwing a code.

thanks for the input, anybody else? I was also thinking it might be the tcm(tcu?)
 
I had that same code when I knocked the TV linkage loose. After I got it back on and adjusted, the rpms were still going wild. So i pulled the battery for a few hours to reset the computer. Havent had the code since and its driving normal.

So in my case, it was more of an electrical issue rather than mechanical. Not sure if thats your issue but maybe worth a shot?
 
Im a jaguar techncian and we see P0741 all the time in our XJ and XK's and its always a torque converter clutch problem fixed with a new converter.

Now i know a jeep and a jaguar are completely different animals, but its just an idea. I would check check fluid level and what rammie was saying before you go replacing the torque converter but if that doesnt work, I would suspect a converter.
 
Last edited:
EDIT: I just looked up the code and a P0740 is for torque converter clutch circuit performance- meaning its an electrical problem, NOT a mechanical problem. Sorry for the confusion.

I would disconnect the battery for ten minutes or so and drive it again to see if it was just a low battery voltage messing with the computer or something. If that doesnt fix it, visually check the wiring to see if its rubbing through somewhere and if you can, check the wiring integrity with a multi meter from the solenoid to the TCM (for high resistance, short to ground, cross short, and short to power). If all is good its either the solenoid or TCM.

Keep us updated.
 
I believe the P0740 code is generated when the TCU does not see a drop in rpm when it attempts to lock the t/c. Since you just checked out the solenoid and wiring, I think you are on the right path. I would try adding the override switch to disconnect the solenoid from the tcu and apply +12volts. Or have a meter hooked up to the wire while driving to see if the tcu is indeed applying 12volts to the solenoid. You could cheat and put the xfer case in neutral and do this in the driveway too.

The advice from igotanxj seems pretty good, although a plugged valve body or damaged t/c lockup mechanicals could still be the problem. I'd bet on a solenoid, wiring, or bad tcu first though. I don't believe the NSS is the culprit, btw.
 
Thanks for the input everyone, keep it coming. I checked the wiring and the connectors and cleaned them all with electrical cleaner. I also readjusted the TV cable.
Lawsoncl, I think next I am going to try testing the voltage from the tcu. I didn’t realize I could do this in the driveway. Are you saying leave the tranny in Drive & put the transfer case in neutral? Is rpm’s the factor here?
I have also read your previous post in regards to a switch on the brake pedal that also controls lockup of the torque converter, but it was referencing older model jeeps(89). I have looked at mine(just one switch, not two) and it seems to be functioning ok, is there anything different I should be aware on a 2000 model?
Thanks again
 
I've also pulled the battery cables to reset the code. I'll leave them unhooked overnight but the CEL still shows up as soon as I turn the jeep on. the CEL will disappear for a while if I clear it with a scanner but it always comes back. I've got 5'90s battery cables and grounds, so I think I'm ok on the juice side of the house.
 
00XJmike said:
Thanks for the input everyone, keep it coming. I checked the wiring and the connectors and cleaned them all with electrical cleaner. I also readjusted the TV cable.
Lawsoncl, I think next I am going to try testing the voltage from the tcu. I didn’t realize I could do this in the driveway. Are you saying leave the tranny in Drive & put the transfer case in neutral? Is rpm’s the factor here?
I have also read your previous post in regards to a switch on the brake pedal that also controls lockup of the torque converter, but it was referencing older model jeeps(89). I have looked at mine(just one switch, not two) and it seems to be functioning ok, is there anything different I should be aware on a 2000 model?
Thanks again
Click to expand...

Yes. The tranny computer has no idea if you are moving. On a 2000, it only sees the input shaft rpm and the output shaft rpm. I'm not sure about the brake switch on the later models. I think it's tied into the same switch for the brake lights. If you have the FSM, you can look to see what pins to check for a voltage change at the TCU when you hit the brake pedal.
 
Replaced the tcu(tcm?) today with one from the junkyard, disconnected the battery to reset the computer, still no change. The CEL came on within 20 minutes and I still have no torque converter lockup.
What are the chances that this is actually a bad torque converter? If it was the tc or even the valve body wouldnt I be having other issues? It shifts perfect, just no lockup.

:banghead:
 
anybody have any good wiring diagrams for a 2000? I dont have a FSM and the diagrams I have found online are either lousy or pre '96.
thanks
 
ok, now I am really confused. I checked the voltage going to the torque converter solenoid and it was 12-13 volts. Engine was idling,tranny was in drive, transfer case in neutral. The voltage did not change when the engined was rev'd to 2000 or 3000 rpm or idling below 1000 rpm. My understanding was that the solenoid did not receive power(locking the torque converter) until the jeep reached a certain rpm and was not under load.
Any thoughts??I am really pulling my hair out over this.

 
The t/c will lockup at pretty much any rpm if you're not giving it any gas. Is it getting voltage when the tranny is in park? Sounds like you're getting voltage to the t/c in any case.
 
It is getting voltage while in park. It also provides same voltage while giving it gas. all three solenoids are getting voltage, all between the 12-13 range. If I unplug the TCM, then I dont get any voltage, obviously.I am taking these readings from the plug-in connection in the engine compartment passenger side rear of engine. If I am understanding the fsm(for 2000 XJ), it is a a DB/WT (for tc solenoid) OR/WT and WT for the other two solenoids. I checked the OHMs again for these same wires(while the jeep was off) and they all came up between 13-14 ohms.
 
Are you unplugging the wiring harness at the firewall to measure the voltages? It believe it needs to be plugged in to get a proper voltage measurement.
 
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