D4 light & error code 43

[laloquera]

D4 light keeps coming on and staying solid, no error codes. I only get 1st & 2nd gear. I pull my back up radio fuse to reset the ecu and it runs perfect till maybe an hour of driving it comes back on and Im back to lower gears.
So far I have done the following:
swap out both A & B solenoids, double check the plastic connectors to be cleaned and clean all ports in the tranny
swap out old tranny fluid for new one.
Inspected my ecu, and connectors. (all good)
Inspected main relay. (all good)

Error code 43: My car would tumble and loose power while traveling 55mph after I swap out a new 02 sensor the loose of power was more noticeable at 35mph and had no more issues at 55mph. Weird huh?
Check for vacuum & intake leaks.

Are this two issues related or separate? Gonna go after the error code 43 before my D4, maybe one will cancel the other out.
Help Help.

[deevergote]

What o2 sensor did you install? Are your wires spliced? The code 43 is USUALLY an o2 sensor code, but not 100% of the time. I've seen the fuel pressure regulator be the cause for it occasionally, though rarely.

Check your spark plugs. They can tell you what has been going on inside your engine. It's possible that if there is a fuel issue, you could have been running lean... which should be evident on the plugs.

The first thing I would do is replace the fuel filter. Eliminate that as a potential fuel system issue. Next, I would try the fuel pressure regulator (I don't know how to inspect or test it, so I could only suggest replacing it.) Finally, the fuel pump. Also, if you just pulled out your main relay and looked at it, that may not have been enough. Sometimes the main relay has microscopic fractures in the solder... enough to cause problems, but not enough to see without magnification. Get your hands on a good magnifying glass, or a jeweler's ring. Or just resolder the whole thing (if you know how to do it properly...) OR try a known good one.

I have no firsthand experience with automatics, so I can only go by what I've read on here... but I've seen people mention a ghost D4 error that ended up being related to the main relay. Since the main relay is fuel-related, it's possible that a legitimate fuel system error COULD set the D4 off.
I'd focus on the CEL for the time being. Get that sorted, and see if the D4 error continues. If you have access to another known-working TCU, that might be worth a shot, though.

[emosun]

yea just sounds like the tcu is dead.

[laloquera]

I do not have a back TCU, but I will crack my open tomorrow and take a look inside.
If I reacall, the last tune up was done last May, I did noticed some white, pinkish frost on some of my spark plugs.
I will post up and keep you all in the loop of things.
Thanks
PS
Should I check the TCU TCM, the other box?