Jeep Description: 1999 Jeep XJ, 4.0L, AW4 Transmission with 161k miles showing P0743 and no overdrive/torque converter lockup on the highway.

Background: The transmission overheated last summer because I was driving like an idiot and the return cooler line was kinked. The fluid was black and burnt. I changed the fluid, replaced the lines, and installed an auxiliary cooler. A few months later intermittent CEL with error P0743 and no TC lockup. Now the light is always on and Jeep will not shift into overdrive. No other CEL lights or issues currently.

I searched and read the posts on the P0743 error. I replaced the three solenoids in the transmission. I also conducted the voltmeter test of the transmission control module as explained here (thank you CCKen): https://www.cherokeeforum.com/f2/p07...re-out-231689/

I think the next step is replacing the torque converter, but the Jeep drives and shifts fine except on the highway. The transmission is tight enough that I can still light up the rear tires on dry pavement.

Question: Did I damage the torque converter and do I need to replace it even though the Jeep drives fine in the city and I cannot detect a slip in the transmission? Or do I need to focus on something else?

Thank you in advance for any help. I have been using the tech answers on this forum for years to rebuild my Jeep and your knowledge base in invaluable.

 

I appreciate any input or thoughts. Am I way off base on replacing the torque converter if tranny takes off and stops fine? Is it even possible to damage a TC so the only problem is that it doesn't shift into over drive?
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Well, there are a couple of ways to approach this. You could just take it to a shop and pay a bazillion dollars to have them replace the transmission.

OR, you could go the cheap and easy approach, and if that doesn't work, work your way up to more expensive fixes.

I'd start with a transmission fluid replacement. It might be all you need. See my sig, #3, for that.

Next, check your solenoids. They are not hard to test, not hard to replace, and not terribly expensive.

Chances are good that you'll solve the problem. If not, it's probably time to replace the TC.

 

Thank you Blue Ridge. I am going to use your method of flushing the entire tranny system this weekend and will report results.

 

Yes BlueRidgeMark is giving very good advice .

 

I drained and refilled the transmission pan then flushed the remaining fluid using the return line disconnect method suggested by Blue Ridge.

There was slightly more than 3 quarts in the pan and between 7-8 quarts out of the return line before fluid went clean. If you are going to flush your AW4, I recommend buying 12 quarts so you don't run out.

Here is a pic of my drain set up.




I marked quarts on a gallon jug so I knew how much to refill. Pumped out 2 quarts then refilled 2 quarts. The tranny pumped much faster than I thought and filled two quarts in 10-15 seconds.

Here is a pic of the fluid. Left is the fluid after tranny over heated, middle is after draining pan twice, and right is after draining + pumping 8 quarts.



Changing the fluid did not solve the lack of overdrive. So unless there are other suggestions to try first, I am going to replace the torque converter.

 

Don't forget it has a solenoid that controls it .

 

I already replaced the three solenoids and tested resistance/continuity of the TC lockup solenoid at transmission control module. It tested within spec (I can't remember specific ohm now).

I also ensured that the brake switch wasn't engaged.

 

Well, sounds like you have covered the bases and it's time for a TC.

At least it will be pushing clean fluid through a clean transmission.

 

Update on the AW4 transmission that does not shift into overdrive on the highway and shows error code P0743 - Mechanic determined that there is an internal problem with the transmission and a new transmission or rebuild is necessary.

He recommended that I continue driving the Jeep as-is because the transmission functions perfectly except for overdrive on the highway. Said that I was not doing any damage to the transmission by driving it without OD.

Conclusion - I lost overdrive on my transmission because it overheated and burned the fluid. Despite fully flushing the fluid, adding an auxiliary transmission cooler, and replacing the solenoids, I was not able to fix the issue and will continue driving without OD.

Thanks everyone for the help.

 

Deleted repost

 

Update- The torque converter finally gave up the ghost. For past month the Jeep vibrated when accelerating 0-30 mph. Then yesterday I heard ticking sound when driving up ramp in parking garage. Limped home and the ticking turned to metal rattle and clanking. I took this video in my garage at home with Jeep in drive and parking brake on: https://youtu.be/NM-8jNM-8jANUdG

Not sure if you can post yt links here, but you can hear the destruction.



​​​​​​Here is a pic of the old girl getting towed to mechanic.
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