I've got a 93 accord lx 4dr with the 4cyl and an automatic tranny with 197k on the whole car. My wife was driving it home from work and it dropped down into 2nd gear and there it stayed. I've taken it out for test drives and 9 out of 10 times it would work fine on a cold start, but even warmed up and at operating temp, for 5 or 10 miles and then drop into second and stay there, one time it didn't work right right from the get go. I am not getting any flashing D4 light or cel, if I jump the the two pins on the service connector I do get a 15 code from the D4 and no codes on the cel. I pulled the nc and nm speed sensors and cleaned them up and tested them, they both read 500 ohms, I put them back in and drove the car and it worked good for 13 miles and then would drop into second when my foot was off the gas but I could get it back into its proper gear if I gave it some gas for a few more miles until it was finally stuck in second again. My tranny fluid is clean and full and has 15k on a change. I jumped the solenoids and they all seem to have a good click. I pulled the tcu apart and all the resistors and caps seem fine. I hate to throw $90 at a new speed sensor if I don't know its bad, any way to tell besides checking the ohms? Any help would be greatly appreciated, thanks.

 

I am not sure which sensors you tested for resistance.

The main shaft speed sensor is the code 15 and the resistance should be 400-600 ohms at the connector. The resistance should also be close to the same reading when measuring the resistance between D12 and D19 pins at the ECU connector.

 

I don't have a wiring diagram of the tcu and tranny components, if anyone knows where to find that that'd be awesome. Is the main shaft speed sensor on the firewall side of the tranny on the far passenger side of the car, and is the one on the radiator side the countershaft speed sensor? The one on the firewall side read 494 ohms at the connector and 488 ohms at the tcu right connector 2nd wire from right on top bluewgreenst and the 3rd from right on top bluewyellowst. The sensor on the radiator side of the tranny read 499 ohms at the connector and 498 ohms at the tcu right connector middle bottom wire whitewbluest and right top wire orangewbluest. Does this mean the two sensors are fine and not the problem if the read the right ohms?

 

Look in the DIY section - sticky post about on-line manuals. That'll have the diagrams & troubleshooting charts & stuff like that.

 

Thanks, that's a much better manual than my chilton! I went through the troubleshooting chart for both code 9 and 15 and everything checked out ok, both have resistance around 500 ohms and all the wires have continuity. The end of the flow chart mentioned either possibly a faulty tcu or mainshaft, how do you check that or any thoughts on those scenarios? I've opened up the tcu and it appears to be fine? Also if I'm getting a code 15 shouldn't my D4 light flash at me or stay on as an indicator of a fault code when driving? It doesn't, functions as normal. Any thoughts on were to look from here?