I have researched a lot into the transmission problem for the 2G TLs. 2000 TL, currently at 190,000km (~118,000 miles). Hard shifts all the time throughout last week and now it's always stuck at 3rd gear (safety mode) with flashing D5, check engine light and TCS light on. Codes from interface reads solenoid fail. Anybody has experience on how to determine if it's the alternator causing electrical signal issues or transmission failing itself?

Alternator side:
New battery this summer. Never had a problem starting. No problem cold starting. All electronics works flawlessly.

Transmission side:
Last month, had its first major gear slip. More severe a couple of weeks back. Currently always slips, hard shifts (can't get into gear). Gearbox in protection mode (flashing D5 with gear locked in 3rd).

I will take the car to test the alternator as soon as i can, but i don't drive it more than a couple km. Its not safe because it'll loose torque (power) when the gearbox slips.

 

Doubt it's anything to do with your alternator. Sounds like you have some transmission issues. I would get the codes read first and report back

 

Last time the trans had a 80% or more fluid change, trans filter, and current condition of ATF?

 

^ That. Also, if it's an electrical problem, you could always check your grounds and test your solenoids. But it's more than likely the classic failure problem.

 

flushed the ATF within 12 months / has about 25,000km (15,000miles) on that fluid. Not sure if they have changed the filter, (i did the flush at Acura dealership). Current condition of the ATF fluid is like new.

 

get the codes read, invest in a simple 20$ amazon code scanner and it will pay for itself in the first use! no longer will you be screwed over by a check engine light! pays for itself in beer too helping your friends...

 

The A/B linear solenoid can cause shifting issues as it ages.
Also if you have a bad front engine mount the black connector on this solenoid can come in contact with the battery tray breaking the connection sending the trans into limp mode.

Lastly check the ATF level and post the codes here when possible.