I've got a 1993 accord lx with 197,000 miles, 4cyl auto. It shifted down into 2nd gear at hwy speeds and was stuck in 2nd the whole way home. Fired it up the next day and it ran fine for the firtst 10 miles or so and then stuck in 2nd again. I jumped the service connector and got a code 15 on the d4 light. Mainshaft speed sensor, checked both the mainshaft and countershaft sensors and the both read 500 ohms at the sensor and at the tcu, no shorts to ground and the wires have continuity. I swapped out the mainshaft speed sensor with a known good one and no change, swapped out the tcu with a known good one and no change. I drained the tranny fluid, which was dirty but not terrible there were tiny metal shavings on the plug but no chunks, no change. I've tested the shifting solenoids and lock up solenoid with a jumper wire and they all have a good click to them. Tomorrow I will get a gasket for the throttle body and swap that out to check the tps. Any ideas if that doesn't do it? When I reset the computer usually after sitting a day it will run like a champ for 10 to 15 miles even cruising at 65 but then I get on the highway and get up to 65 and it drops back down into 2nd and is stuck there again, I don't know why it tends to do it on the hwy 8 out of 10 times I usually have to sit at a light for a minute or two before I can turn onto the hwy maybe that has something to do with it? Does this sound electrical or is there a chance something mechanical is wrong with the tranny even though it works perfectly at first. Sorry for the long post, thanks for looking, any help would be greatly appreciated.

 

It certainly sounds like an electrical problem to me.

From your writeup, you went through the entire tree of the diagnostics from the shop manual. In the code 15 tree, it redirects you to the counter-shaft speed sensor. I wonder if replacing that will fix your shifting problem?

At least remove the counter-shaft sensor and clean anything that impede its signal? Maybe twist the pins a bit leading to main-shaft and counter-shaft speed sensors to make sure that they have a good contact. Check that the pins on the connector leading to the TCU are not loose?

 

Thanks PAHonda, it sure seems electrical. I did go through the flow chart on the countershaft sensor as well and it checked out fine, but definately worth a try. I've pulled both sensors and cleaned them with no results, when I later swapped out the mainshaft sensor it already had alot of little shavings on it again after maybe 30 or 40 miles, is that normal?

 

I was listening to Car Talk about a transmission computer shifting problem and they suggested checking the ground connections. If no problem there is found, they suggested running a new ground wire from the firewall to the engine block.

 

bro i have the same problem on my 97 accord lx i swapped a jdm f23 vtec motor with the old lx tranny and everything else that the swap needed from the old f22 non vtec and now the damn tranny is stuck in 2nd and it gives me the countershaft speed sensor code but i got a couple of them from the yard and it never worked!! now i just left it unplugged and it revs kind of high but it changed gears but only at like 5000 rpms then it shifts, i hate automatic accords!!

 

I beginning to feel the same way. My 93 has been in the garage now for 2 weeks waiting for a replacement of the tranny computer. They put a used one in and it also had problems, so now they're trying to find another one. I really shouldn't complain, though. It has 235,000 miles on it and so far has been fine. I remind myself that if it was a manual tranny, it probably would have needed a couple of new clutches by now.

 

If goes to "fail safe" mode when it warms up, can you check the resistance again when this happen ? It might have a different reading when warm.