Seems like my car keeps getting worse and worse...I think I really just need a new car but I was trying to hold out till I graduated this May.

My CEL is on so I went and got it read because my car isn't shifting gears. These are the codes and the explanations I was given...

P0740:
TCC does not engage (probable cause)
Open or short circuit condition
Poor electrical connection
Failed TCC system

P0730:
Faulty shift control system (probable cause)
Low transmission fluid level
Poor electrical connection
Failed transmission shift control system

P0420:
Catalyst system efficiency below threshold bank 1 (probable cause)
A/F ratio concern
Air leak near HO2S
Ignition System Concern
Faulty catalytic converter

All I do know is I was getting P0420 code before I cleaned out the manifold. I recently changed the transmission oil. I know that it calls for changing it 3x, but I could only do it once, but there's adequate amount of oil in there. If I remember correctly I having another problem before and it was fixed by me changing the radiator cap. Are the radiator caps from AutoZone good to buy or should I invest in a different one?

 

If its not shifting gears it could be ECU related or just mechanical- bad transmission. Check your electrical connections to your ECU. Have you done anything to the car that may have caused issues?
Based on the first two codes it could just be a bad transmission really, if so you can do some tests for that. Your torque converter could be bad and its messing up the shifting as well. But I don't know a lot about automatic transmissions.

You can also try looking up the VIN for any recalls.

As for the last one, thats an easy one. Most likely your cat converter. You have a few options based on your ability and time.
A. You can take out the cat converter and soak it in soapy water
B. You can run cat converter cleaner through the system
C. You can replace the cat converter

Because that code triggers when the converter reaches the threshold of 6% "clogged" its not a big deal and usually can be fixed if enough of it is cleaned off.

 

What brand of transmission fluid did you use?

 

No I have not did anything for this to happen. The last thing I did to my car was change my brakes, rotors and do an oil change. Then change my transmission fluid because I started getting the P0730 code. After that I now gained an additional two codes. How do I check the electrical connection to the ECU?

I used the Honda Transmission Oil that you're supposed to use.

 

A big part of my cars issues has been the grounds. The ECU ground on the f22s is through the intake manifold. Factory grounds suck anyways cuz theyre small wires onto the painted chasis. But this is a long shot. I dont think transmission issues are gonna be cuz of grounds unless you had other issues. So I partially take that part back. If you wanna humor me, you can make sure that the wires bolted to the chasis are all secure. Sorry my mind goes all over the place...

Id say take care of your cat converter. If you wanna take it out and clean it, you can, or you can try cat converter cleaner. I can only find one kind, specifically for cat converters, on amazon. Its like $20 shipped.
The other two codes are your transmission. Torque converter issues. Id google how to test for a bad torque converter. Worse case scenario is that you need a new transmission. Buy it from a upullit or something. Itd be a few hundred plus the installation. Rather pricey but you wont have to worry about that again.

Look up your cars vin to see if theres been an issue with the transmission.