buffet_fan2002

1994 Honda accord ex, automatic transmission, w/ 221,000 miles.

The transmission shifts smoothly between all gears, but when slowing down to around 15-20 mph, and then re-accelerating, the car downshifts somewhat erratically, unless I'm super gentle with the throttle. It only really does this once the car is warmed up. It's pretty hard to explain...it possibly downshifts to too low of a gear, RPMs spike (3,500-4,000), and then it shifts back to the correct gear. It's not necessarily a slip, because the car doesn't start losing power, as if it's in neutral...the transmission just seems somewhat confused for a second or two. The transmission fluid has been changed three times in the past 2 months, each time at the Honda dealership. Fluid has looked great each time it was changed. It never really downshifted like this until that initial transmission fluid change about 1,500 miles ago. Trying to be pro-active about it, I took it to a transmission specialist, and he said no codes came up and the car drove fine. Took it to 2 other mechanics, they both said they felt what I was talking about when they test drove it, but couldn't help me...and both repeated that no codes came up.

My main question here is when I check the transmission fluid level, by following the manual's instructions (car warmed up, parked on level surface, engine turned off), the fluid level on the dipstick is above the highest line/hashmark. It's not significantly higher, but it's definitely above it. Could a little too much transmission fluid be causing this downshifting I've never experienced, or possibly causing more damage?

MAD_MIKE

There are two sensors called NM and NC. They are both attached to the right side cover of the AT transmission. These are simply hall effect type devices. Over the years/miles the magnets may become coated in ferrous material from the wearing of the various gears, clutch packs, synchros etc and this material begins to affect the resolution of the signal that the computer 'see's.

Simply removing these two sensors and wiping them clean will usually bring the resolution back and the transmission will shift normally again.
But when you remove these two sensors the original O-rings will be hardened and will not reseal after being disturbed, you will need to replace them.
Four bucks, the horror
For more info check the techauto link in my sig under H4A Troubleshooting, scroll down to NC/NM speed sensor, code 9/15.