Hi! 92 honda accord lx with 220k miles has the dreaded "D4" light, won't shift right issue. Diagnosis steps so far:
1. Removed, cleaned and tested all shift solenoids. Found them cleanish and perfectly functional.
2. TPS tested functional
3. Main Relay removed and joints re-soldered. Tested functional.
4. TPS removed, found to have blown capacitors as per the usual TCU problems with these components. I replaced the blown capacitors and resistors that are the usual culprits. Re-installed TCU....DID NOT HELP! I readily admit I could have done a bad job and that could be the problem, but it looks good.
5. removed and replaced brake pedal switch. Don't think it was bad, but might have been.

Symptoms: limp mode, doesn't shift right. With the transmission in D4 it starts in what must be 4th gear. I can get it to 1rst gear by shifting into manual mode. Sometimes loud clicking near/under/behind dash. Sometimes it'll shift out of park when I press the brake pedal, sometimes it won't.

Questions:
1. Is there anyway to bench test this TCU?
2. What am I missing?

I've got new tires, new struts, brakes so much work done on such a great car and I can't drive it. It's driving me! Crazy!

 

Find the two wire blue connector located above the passenger side kick panel.
Jumper the connector with a wire.
Turn the ignition to II(ON)
Watch for any trouble codes from the CEL or D4 light and record them,
Post back here for further diagnostics.

 

[QUOTE=MAD_MIKE;51268033]Find the two wire blue connector located above the passenger side kick panel.
Jumper the connector with a wire.
Turn the ignition to II(ON)
Watch for any trouble codes from the CEL or D4 light and record them,

MIke, thanks for the help. I've reset the ecu and tried to find codes many times, no codes. NOw it's like it's possessed! Clicking like mad underneath the dash, flashing on and off, and the shift lock mechanism at the shifter is clicking on and off incessantly. here's a link to a video of the crazy...

 

Verify that the underhood memory/clock fuse for the ECU/TCU is not missing/blown. If so then no codes will be stored.

The flashing D4 and clicking interlock have me wondering if there is a faulty ground or other connection. When shifting from Park to any other gear does the dash indicator show what gear you are in?

 

Mike, yes they do show, all but the D4. When in Drive (D4) nothing is lit. All other gears show the proper position. I cleaned the shift position switch too...

That being said, yesterday I went out to start and run the car (keep battery charged, seals lubed, drive it around the block in limp mode...) and I let it run for 10 minutes or so...when I came out to drive it, IT SHIFTED PERFECTLY AND BEHAVED IN A NORMAL FASHION FOR THE FIRST TIME IN MONTHS! Couldn't believe it. Parked, turned off, checked trans fluid level (since I had it at operating temp for a change), restarted and drove off like a champ. BUT. After it cooled off I tried again...same stuff. Clicking from under dash, D4 light flashing off and on, won't shift out of park, etc. WTF???