You've done quite a bit of work. The thread is getting long. Briefly, what transmission and engine code(s) do you have and what symptoms (If any) are you observing while driving?

I hope this is brief.

Briefly okay. There are 3 TCUs.

1. Junkyard TCU
2. Original TCU
3. Another Used TCU I got in the mail.


Junkyard TCU had some symptoms of D4 Solid and some slight acceleration not the best it could do symptoms. Could be reset sometimes by unhooking the battery. Until it comes later. Now I wanted to repair this TCU. Instead I repair the original TCU I had kept for so many years. Not knowing those original symptoms of that TCU that was replaced in what year I can't remember?. So anyways the Original TCU was sent via mail to be repaired. I got it back, it didn't seem to fix the problem. And also I didn't really check TCU codes.

Now some months later I decided to replace the shift solenoid and lock solenoid to see if that would fix the problem. Granted at this time I didn't check TCU codes. I just did this fix hoping it would solve the problem. Again, it never fixed the problem either. I just kept driving it for a while with D4 solid issues. Now come the D4 issues again this time blinking. I figure out that is giving out a TCU code for the Shift Solenoid. Code 7. So sometime down the road I decided to replace the shift solenoid again. I figure out the wire is damaged on the shift solenoid. I figured that would solve the issue. Nope, it still brings up a code 7 for it.

Now at this time, I theorized what would happen if I put the junkyard TCU in. Would it show that code? And then I would again replace the original TCU with a used one. And I figured the junkyard TCU could be broken as well. I can't get confirmation on that although. Anyways I put the junkyard TCU in, instead it brings up Code 15 (and car wont go up above 20 mph without revving). I ignore the code, thinking it's just another bad TCU. I buy another used TCU thinking that would solve the problem. I also put original TCU back in to see if my acceleration was fixed and it was.

Now I get the other used TCU from the mail. And it has the same problems. It brings up code 15. So I figure I better research code 15 mainshaft speed sensor. I found it and took it out of the car and tested it. And waiting to see if the replacement will fix code 15.

What are the first 8 digits of you VIN?

What the the OEM part number on the TCU you are using?

VIN is:
1HGCB765

TCU is
28100-PX0-722

CV axle boot status: split because I jacked up my car? Picture proof, I took a picture of my sensor which accidentally took a picture of my cv boot (not ripped). The whole thing ripped later (possibly when I jacked up the car or when I went under the car to find the sensor) in a full circle. *Replaced 2 years ago.
Part status: wrong part sent.
Weather status: cold.
My mind status: ?
Theory status: I don't know what ripped my cv boot!


I better update this to avoid confusion :

28820-PX4-024 is Mainshaft Speed Sensor (NM) Which is the grey connector. Shows on hondapartsnow on the diagram. Which is TCU code 15
28810-PX4-003 is Countershaft Speed Sensor (NC). Which is the green connector. Shows on hondpartsnow on the diagram. Which is TCU code 9.

The picture I showed on the previous post of the green power connector of the (Countershaft Speed Sensor) (NC) wasn't the one I took out. I just showed that picture because I unplugged both the mainshaft and countershaft speed sensors. I just wanted to show the rust and how I made a small cut to free the rust. I had a better picture with the (Countershaft Speed Sensor) (NC). As I wanted to test the voltages on both speed sensors. I just wanted to replace the one that the TCU is indicating.

Now I don't know why on earth they just don't want to label the parts Mainshaft Speed Sensor or Countershaft Speed Sensor. When you go buy the part. They might label it as input or output sensor.

So if anyone is having the same issue I'm having. Be careful! They want to over charge you for these parts! And the thing is you don't know if these parts will fix your issue. So why pay extraordinary high prices for them!?

I just wanted to verify you had a 93 accord, and by the VIN you definitely have a 90-93. I needed a few more digits to verify the year.

Google 62SN700.pdf to get a 1993 shop manual. This covers non-US accords, but should be fairly close if not identical to your US accord.

Jacking up the car shouldn't cause the boot to rip. Most likely cheap material for the boot on an aftermarket part?

With the mains haft sensor error 15, the problem can be the sensor, the wiring, or the TCU. A bad ECU might cause this, but it is a stretch.

For electrical testing, a resistance test is good first test. It can identify open/closed circuits or circuits that are out of range. The problem is a resistance test that is in range and "passes" doesn't necessarily mean the sensor is good. It has to do with how little current is used by a volt meter to do a resistance test.

If the wire colors are orange/blue and white/blue at the sensor, you can try plugging in the sensor and measure the resistance between D12 and D19 pins plugging into the TCU (verify the wire colors at the TCU). You are measuring the resistance of the sensor through the wiring. It should be the same (or very close) to the reading on the sensor. Another test you can try is to unplug the main shaft sensor and use a volt meter to measure voltage on each wire to a good ground (like the - battery post). One of the wires should have voltage (either 12V or 5 V). The other wire should not have voltage.

All my accords were manual transmissions, so I'm not as familiar with the AT specifics. I think that sensor has a magnetic pickup to detect the main shaft speed. Make sure you have no rust/debris in the transmission to interfere with the signal. Cleaning out debris may help with the signal.

Thanks. I guess I will try this:

1. Replace CV axle (might need some help freeing the lower ball joint) 2. Try the car again with the cleaned mainshaft speed sensor (I cleaned the crud on top of it) (I didn't see any metal shavings on the magnet part of the tip when I took the sensor out).( I sprayed some electrical cleaners on the connectors) 3. If that doesn't work try new mainshaft speed sensor (that I just ordered) 4. If that doesn't work, run some electrical tests on the TCU computer and the Mainshaft speed sensor following the wire. 5. If that doesn't work try another TCU.

Thanks for the honda 1993 accord manual by the way! Also the ball joint separator tool didn't work on the lower ball joint it kept on slipping off. Last time I replaced the CV axle. I noticed the ball joint seperator is different in the honda accord haynes manual. That one would have worked. I'm going to look to see if there is any different tools I can borrow at all the local parts store.

Also if all ends well, do transmission fluid change.

If something doesn't end well. I'll just take the transmission out. And I'll send it to you to rebuild. Thank you. Just kidding.

Alright, I tried the car again with the cleaned mainshaft speed sensor. Same result, it wont get past 20 to 25 mph. It starts to Rev really hard. I got back home, I checked the TCU, and it gave me code 15 again. So, I finally get the mainshaft speed sensor (the grey connector) in the mail (new). I hook it up. I take the car for a spin, the same result. I also this decided to really try hard to get past 20 and 25mph. I kept on revving it up, and it eventually it got past 30 mph and the revs went down and I could get it up to 35 mph. It wont be in a constant state of being revvved up if I maintain 35mph. It just doesn't like the acceleration past 20 or 25mph. It must revvv up, maybe 3 to 4 times before it breaks the 30mph barrier. Anyways, I get home and check the TCU for codes. I still get TCU code 15. Oh I also forget to mention I checked the ohms on that new part (mainshaft speed sensor) it was 510 ohms.

Yeah, I have done voltage test, and both the Mainshaft speed sensor and the Countershaft speed sensor power connectors and I get about 0.28 voltage on each. I don't know if that is the right voltage although. I believe the colors are white and yellow on the mainshaft speed sensor. And probably on the power connector coming out of the wire harness it has the same color. If I had a multimeter that had a probe that could reach that far, from the hood of the car to the inside of the car to the TCU. I could do a continuity test. But I already checked for a short to ground when I got voltage coming out of the power connector for both the mainshaft speed sensor and the countershaft speed sensor. From my knowledge if I'm getting voltage from the power connector, there is no short to ground and it's working fine.

I'm not sure what to do now. Maybe I want to go back to the original TCU to see if it behaves normally to make sure. It should bring back TCU code 7. Original TCU still has a broken transistor. And Original TCU still has a hesitation issue on D4 solid now D4 blinks. Maybe it's time for another TCU.


What's kind of weird about the situation is this.

When original TCU gave out TCU code 7 the shift solenoid error code. When I replaced the shift solenoid. The code stayed there even though I replaced it.

When the other TCU that I received in the mail brought up code 15 NM speed sensor. I replaced NM (mainshaft speed sensor). The code still remains.

I might want to switch to the original TCU and see what happens again.


Hmm, I think there is a test at the TCU power connectors for D12 and D19. I might run that.

One of those wires to the mainshaft speed sensor should have 12V (or maybe 5V). The voltage is supplied by the TCU.

Yeah, I got 0.27 volts now with the original TCU.

I did some resistance/continuity testing with ohms with the battery disconnected, and the NM mainshaft speed sensor disconnected, and the 22 pin from the TCU disconnected. Now with the D19 (ORN/BLU) and the D12 (WHT/BLU) terminals I did a continuity test. Nothing happened. Then I reconnected the NM(mainshaft speed sensor) than I switched my digital multi meter to 2k for ohms. And I put a black probe and a red probe with the D19 and D12 terminals. I got no ohms there.

I kind of tried to run probes with alligator clips and using a paper clip on the D19 terminal and the NM mainshfat speed sensor terminal. I got no continuity there either.

Then after that I reconnected the battery and the TCU 22 pin connector. And I tested the NM mainshaft speed sensor for DC voltage. I got 0.27 volts.

After that I decided to re-hooked up the original TCU and test what voltage I get from the NM mainshaft speed sensor. I got the same voltage 0.27 volts. So I re hooked up everything. And I got a D4 blinking light right away.
But when I drove I got not extreme revs. It would accelerate really great. And then when I took it home. It would even go up the small incline in my driveway without me having to push on the gas. I short the test connector. I got TCU code 7.

So I'm thinking I ruled out the speed sensors (NM mainshaft speed sensor and NC countershaft speed sensor) at this point. My theory is I should try another TCU. Perhaps a rebuilt TCU this time. Otherwise might be some other issue. But as long as I got the original TCU maybe I could drive with that for a while. Until I try another TCU. It's running really good so far. The original TCU does have a bad transistor.

Unless there is another theory here? Could it still be the wiring and could it still be another speed sensor on the TCU code 1-15? I'm really thinking these all 3 are bad TCUs. It's just the original is good enough and programmed enough (even with a bad transistor) to run the car without much issues.

If the car is running good, then don't mess with it.

I'm not sure about the 0.27V. Test your volt meter on the battery to make sure it is working. When testing for voltage at the connector, put the black meter lead on battery ground, and the red meter lead on one of the wires at a time?