Hello, I've got a 1992 Honda Accord Wagon EX, Automatic Transmission 142000 miles. I am getting a flashing D4 light. When jumping the diagnostic plug I am getting a TCU Code 10 (1 long blink). According to my manual is "Disconnected water temperature sensor coupler", "Short or open in water temperature sensor wire", or "Faulty Water Temperature Sensor". Its late today and I am going to order one and I'll respond if that fixes it.

Now, what I'm perplexed about. This all started when my wife called me because she couldn't get her car out of park (luckily in the driveway). I pulled the center console out and the shift interlock solenoid was not actuating. I pulled it out, gave it 12v directly from the battery, it did nothing at first, then I was giving and taking away voltage, it started stuttering and then began actuating. Hooked it back up in the car, and it was sort of working, stuttering, but then actuating normal. I decided I didn't want it to fail again on her and couldn't find a replacement so I took it off, and went to take it for a drive. Pulled out onto the road, and all of a sudden I was getting a steady flashing D4 light. So I put it in reverse and backed into the driveway. Plugged it back in, disconnected the battery, drained the system, then started it again. Started the car, the Interlock was working at this point then 10 seconds after startup, flashing D4 light. Jump the connector and I'm getting the 1 long blink, code 10.

Car has never done this before. Ran and drove just fine before the weekend. Today, a day later, same issues. Shift Interlock is not actuating again, and I repeated draining the system to clear codes, even disconnected the lockup solenoid and verified that it created TCU codes 1 & 2 (short blinks, and still was getting 10 (1 long blink). Drained the system, hooked lockup solenoid back up, started the car. Back to only code 10.

Does the Shift Interlock Solenoid circuit go through the TCU? I am struggling to see how these could be related, anyone got any thoughts? Awful odd coincidence if not related.

 

Troubleshooting Flowchart - TA Sensor

 

Appreciate that, but what you uploaded is actually for ECU code 10, not TCU code 10.

Update, I went to pull the connector off the Coolant Temp Sensor (TW sensor in manual) and the sensor itself broke in half. So I replaced it, no change. Still getting flashing D4, code 10. I did however find the TCU code 10 diagnostics flow tree (Figure 1). It checks for (the way I understand it) circuit voltage from the ECU to the TCU (getting 5v as the book calls for), then circuit voltage from TCU to Coolant temperature sensor (getting ~1v as the book calls for). So, this leads me to believe the sensor circuit is functional and would appear to be a TCU issue. Thoughts?


Figure 1

Figure 2

I pulled my TCU apart, and it has had a questionable repair before, I can see (Figure 3). I also see another capacitor the seems to have melted (Figure 4, blue arrow). I found a correct PN TCU online that I'm going to order as it says next step is to replace control unit.


Figure 3

Figure 4


Still curious if anyone thinks the shift interlock solenoid issue, and this code 10 issue could be related? Im having a hard time finding any information about the shift interlock circuit.

Will update again after I change TCU

 

Well, I ordered a same part number TCU from a used parts shop. Pulled it apart when it arrived and it looks perfect. Plugged it in, started the car, now I've got no park indicator lights at all. So I plug the old TCU back in. No park indicator lights, shift interlock solenoid not working still. Pull out of the driveway, shifts fine, but then I realize I've got no tac or speedo.

Dimmer switch is working fine. Dash lights otherwise are working.

I'm leaning towards a ground issue. Gonna clean up all under dash and engine bay grounds and will report back. Gahhh! Hate weird electrical issues. Id rather change a motor😂