I have a 2001 honda accord ex 6cyl, automatic. About this time last year (July-August 2022), my check engine and TCS lights would come on at the same time. The next time I started my car, the TCS light would turn off but the check engine light would stay on. I used my OBD2 code reader and it always spit out P0740. I would reset the light every time it came on, but it would always come on again after about 50 miles, meaning it wasn't just a one time error. Around the end of August 2022, my catalytic convertors got stolen, so I know that's why my check engine light was on a majority of the time, but prior I still don't know why. I got new ones on my car a couple weeks after but my check engine light and TCS would keep coming back on. Towards December I was driving and I believe I had a misfire, I heard something loud and my car stalled, my check engine was back and blinking. I took my car to my mechanic and he said I only need to change my transmission fluid and filter. It's been fine for the past 8 months but last night both of the lights came on again. I check my transmission fluid this morning and it all seems fine. Does anyone have any idea what else I might need to replace or repair? For reference this car only has 109k miles and is only used for "around town" driving. This car has also been kept up to date with maintenance, with a full transmission replacement at around 100k miles.

 

P0740 is for the lockup control solenoid on the transmission. The lockup system is that slight dip in rpm when you hit cruising speeds that locks the transmission to the engine. I can't imagine a bad lockup solenoid would cause the car to feel like it is misfiring.

Scan for codes again just to be sure you don't have another issue on top of the P0740, because the P0740 doesn't cause the CEL to turn on according to the shop manual.