I have a 2000 Honda Accord (approximately 70,000 miles) with a transmission problem. The transmission shifts with no problem when the car is cold. The longer that I drive the car the rougher it shifts. After about a half an hour, the car barely changes gears. Before I take it in for service I want to get an idea of what I am dealing with. Is this a mechanical problem (do I need a new or rebuilt transmission) or is it related to a computer chip that regulates the transmission?
This is likely to be a mechanical problem. On most cars, the “D” indicator light or the Overdrive light on the transmisssion quadrant will flash if there is an electronic problem with the transmission. Since you did not mention that a light is flashing, I will assume that this is not happening on your car.
Incidentally, Honda did extend the transmission warranty on Accords of that vintage, due to an abnormally high number of transmission failures. On the chance that this warranty is still in effect for your car, I would suggest that you check with the dealership’s service department regarding possible coverage.
If there is no warranty coverage, then you should go to an independent transmission shop that has been in business for at least three years (NOT AAMCO, Lee Myles, Cottman, or any other chain!). However, a transmission shop is not likely to tell you about possible warranty coverage, so that is why I suggest that you start at the dealership.
The first place I would check is the radiator. Based on your symptoms, I believe your transmission may be overheating. Many transmissions cool the transmission fluid by sharing the radiator that cools the coolant/antifreeze. It sounds to me like you might need a new radiator or you might have a clog in the lines that run between the radiator and the transmission. It could also be that the fins in the part of the radiator that cool the transmission fluid are bent or clogged with dead bugs and other debris.
If the issue is the radiator, I would get it replaced and then get the transmission fluid flushed from the transmission and replaced with fresh transmission fluid. If the problem is a clog in one of the lines, a transmission flush might solve the problem.
I would start by checking the transmission fluid. When was the last time you checked the transmission fluid? Was/is it low? What does it look and smell like?
Have you had any CELs (Check Engine Light)? Some transmission problems will trigger a CEL and record a code that can be read. Some auto part stores will check and read any codes for free. If you get a code, post it back here (the code like P0123, not the English translation.