Error code P0743

[thebarrabuggy]

I’ve seen heaps of post around the place about a “TCC solenoid circuit” (P0743) error code however i can’t make heads or tails of how to check it or what to do next.

i just installed a second hand 32RH transmission from a 1997 TJ into my 2002 TJ everything has gone smoothly except the external plug for the tcc solenoid. on the second hand transmission the plug was damaged so i replaced it with the one off my original transmission, i have no idea if that’s the reason i am getting this code.

from my understanding it won’t lockup the TC (which is the TC that came with my original 32RH trany since the second hand one didn’t come with one) since there is a problem with the electrical side of the component.
i am in dire need of use of my car asap so i would like anyone’s help

a step by step guide on how to trouble shoot next before i have to pay some to replace the solenoid all together.

please please please

 

[hear]

If you're getting the code, it probably means the computer wants to lock up the TC but it doesn't detect the RPM drop (I believe that's how it's evaluated). So that means that either the solenoid is bad or the circuit itself is bad (or the TC itself is bad). So if you're up to cruising speed in 3rd gear you should see it drop by ~150RPM. And then after it does you can further test it by giving it more gas and watching the RPM's kick up (almost like a down shift) but your speed doesn't really change. That's how you know its working or not.

Unfortunately I don't know of any good tests to diagnose the code. For my money, it's 50/50 solenoid or wiring.

It could be that the solenoid is bad. Replacing it is NOT a bad job. You have to drop the valve body down, but that is not nearly the daunting task you probably think it is. And the solenoid is just on the other side of what you can see with the pan off, and it's just an o-ring fit + 2 screws. The valve body is attached with a handful of screws and it comes right down. Going back in isn't any trick either.

It could also be that there is a wiring issue inside the trans. I had this. One of the wires was rubbed bare, likely from it being routed poorly and I think one of the drums was making contact. If you're lucky, you can just take your connection at the back corner of the transmission and flip it over (it fits both ways) and everything will be back to normal. Reason being is that the +12V wire was the bare one, but when the TCC wanted to turn on it was grounding/shorting against the drum or through the fluid or something. Flipping the connector changed it so the bare wire was the ground wire and 12V was on the fully insulated one. TCC started working & code went away. I would try this first, since it is the easiest by far.

It could also be an issue in the wiring harness that goes over top of the transmission. I also had several cracked/bare wires in that section of harness. I unplugged it all underneath, pulled it up into the engine bay, and inspected/repaired/re-loomed all of it. Fixed a bunch of other issues like reverse lights blowing fuses, too. . This is a bit of work too, but even if you don't find the issue, putting fresh tape & loom on your 27 year old harness will leave you in a better place, and future you working on other problems will have the peace of mind that this section of harness is in good shape.