Rep Power: 0

03 Civic DX BMXA Automatic 4 speed tranny w/ 202k original & never serviced. I recently did the "Drain & Fill" fluid replacement (3 times w/ Honda ATF ONLY) to fix the Transmission shudder that occurred between 35-44 mph. It worked like a charm & that problem was corrected.
A few months later I get the dreaded P0740 code that no one can easily diagnose. In addition to doing the Drain & Fill as I stated above, one or all of these repairs worked for me;

1) Replaced Torque Converter Clutch solenoid ($90 from dealership) CEL came back on after 40 miles

2) Isolated then tested TCC harness pins for grounded wires & cleaned all solenoid harnesses w/ electric contact cleaner.
CEL came back on after 25 miles

3) Removed, Cleaned, Tested, & Exercised the Shift & Linear solenoids. They made a dull click when tested, but after cleaning with break clean they immediately began to make loud & clear clicks while the break clean blasted though the small holes with no obstructions. I was exercising the solenoids with a 12v battery during the cleaning to be sure I cleaned both open & closed cycles of the solenoids. Make sure all your screens are clear & rubber seals are not damaged before you reinstall. CEL returned....

4) My last attempt to resolve my P0740 was to clear the CEL yet again & Drive In D3 for a day or so not going above 50 mph to keep RPM's somewhat low. This way it doesn't engage the TCC at all. CEL hasn't come on since!!! & I've driven over 300 miles in the normal D mode with no more pending code. I even had the car Inspected which I couldn't do with a CEL on.

Hopefully, after 2 months of brainstorming I'm out of the woods. I can't say for sure which one ultimately was the fix but all other roads led to a complete rebuild. Most of the trannys with these codes are still good, its just dirty fluids or solenoids. Fluid levels in all Hondas are to be checked at normal operating temperature 1 minute after car is turned off. I believe cold level should be near bottom of cross hatched area & top of when hot. If nothing else, at least I passed NYS Inspection for another year. I'll keep you updated.

 
Rep Power: 133

I went through the same scenario with an 2001 Odyssey. Changed ATF with Honda ATF according to the schedule. Changed pressure switches and solenoids and even added an external Magnefine ATF filter. Traded the van in after trans acted very bad and scary.

What has been the ATF maintenance history of your car prior to the 3X drain and fill? P0740 is mainly a restriction in hydraulic pressure due mainly to clutch debris clogging the internal filter, solenoid screens and ports.

 
Rep Power: 0

I bought the car 10 years ago for my sons first car with 100k on it. I was from the old school where you never messed with the tranny fluid. I know now that's a vital part of keeping these cars reliable. With a little common sense routine maintenance these can go 300k+.
Your diagnosis of the P0740 is spot on & one of the few problems that can send this code. Unfortunately the filter is not accessible unless you do a tear down. Its what they call a lifetime filter...
About two years ago my son bought a brand new Civic coupe & gave me the ole 7th gen beater. Its my train station car. I replaced & cleaned many parts because it keeps me busy, learning & out of trouble. She runs smooth as silk & gives me over 400 miles per full tank, which I think is 12 gallons. Easy to find parking compared to my Ram truck too.

 
Rep Power: 0

Forget it, CEL is back on...
At least I got the inspection done...

 
Rep Power: 0

P0740 code has remained off for over 2k! Has a slight hesitation shifting when cold, but when warmed up all is good. I think it eventually flushed out any debris clogging filter by driving in D3 in city & D on highways above 45/50mph for about 1k. Now light stays off & I drive in D always again.