D4 issue....Got symptoms and don't know what they mean.

[Tuner4Life]

I just bought an unmolested CB7 a week ago and started having a constant D4 indication yesterday. Did a ton of research and learned to jumper the service connector plug. This is where it gets interesting.

I did the jumper and got 2 blinks...I learned this meant "Defective Lock-up Control Solenoid B" I'm not sure what that means, but the constant D4 indication went away so I pulled the jumper and took it for a spin and everything appears to be back to normal with the auto tranny. Initially I thought it was the TCU or shifter switch going and i'm really just seeing if I should go ahead and replace it or not. If so, what TCU's are compatible with my model. It's a 92 LX with the F22A/ auto tranny.

Please, no flamespraying. I'm generally a domestic guy but love anything with potential so while my cobra sits, I figured i'd get a reliable project to start building up. Thanks for the help.

[AbsurdNY]

If I was you, I would test and replace the lock-up solenoids first before replacing the TCU if you are getting a trouble code for the solenoids.

TCU code 2 possible causes:
Disconnected lock-up control solenoid valve B connector.
Short or open in lock-up control solenoid valve B wire.
Faulty lock-up control solenoid valve B.

The lock-up solenoids are on the front of the transmission.
This is what they look like:



Test the solenoids using the image above as a reference.
Disconnect the lock-up solenoid connector from the wiring harness.
Connect the No. 1 terminal of the lock-up control solenoid valve connector to the battery positive terminal. A clicking sound should be heard. Connect the No. 2 terminal to the battery positive terminal. A clicking sound should be heard. Replace the lock-up control solenoid valve assembly if no clicking sound is heard.

Removing the solenoids.


Remove the mounting bolts and lock-up control solenoid valve assembly.
NOTE: Be sure to remove or replace the lock-up control solenoid valves A and B as an assembly.
Check the lock-up control solenoid valve oil passages for dust or dirt and replace as an assembly, if necessary.
Clean the mounting surface and oil passages of the lock-up control solenoid valve assembly and install a new filter/gasket.
Check the connector for rust, dirt or oil and reconnect it securely.

Here is the general area where the lock-up solenoids are located:

[Tuner4Life]

Checked it, solenoids work

Thanks for the advice, nice to know how to do that now. However, that procedure indicated that the solenoids are good so i'm starting to lean towards the TCU. What do you think?

[AbsurdNY]

I don't think it is the TCU because that code is coming up. You should try testing the resistance on the solenoids.

With a multimeter set to ohms, measure the resistance between the No.1 terminal (solenoid valve A) of the lock-up control solenoid valve connector and body ground, and between the No. 2 terminal (solenoid valve B) and body ground.

I do not have my service book on me right now but if you post up the resistance numbers I will check the book in a little while and tell you if they are within spec.

[Tuner4Life]

Resistance readings

4.63 ohms and 4.61 respectively

[Tuner4Life]

More readings

I wasn't sure if i was taking the readings from the same plug i tested the solenoids on or not so I decided to include readings from both sides of the plug. The plug that goes directly to the valve in the picture reads 15.4 and 15.3.

[AbsurdNY]

4.63 ohms and 4.61 respectively

In my service manual it says the resistance should be between 12-24 Ohms so that might be your problem.

Here is another test to check for faulty wiring although It seems like you do have bad solenoids. I will post this so you can check the wiring from the solenoids to the TCU after you replace the solenoids.

Check for the solenoid resistance at the TCU harness and ground.
Read the wire color on the solenoid. Go to and disconnect the TCU wire harness at the TCU. Locate that wire color. Measure for the resistance to ground. It should be pretty much the same Ohms as the resistance at the solenoid connector.

Edit*

I wasn't sure if i was taking the readings from the same plug i tested the solenoids on or not so I decided to include readings from both sides of the plug. The plug that goes directly to the valve in the picture reads 15.4 and 15.3.

Ahh there you go. That resistance seems good. Now follow the steps I posted above to check for faulty wiring.

You will have to pull up the passengers side carpet and take off the ECU/TCU cover and locate the TCU. It is the unit on the left side.

If the resistance at the TCU is pretty much the same as the resistance at the solenoid, the only other thing I suggest you do to the solenoids is take them off and clean them.

To clean the solenoids, use carb cleaner and at the same time, connect a 12 volt battery (use the metal part on the solenoid as the ground) and click the solenoid on and off.
Make sure the screens and the openings on the transmission are clean.
Clean the gasket with soap and water. DO NOT USE CARB CLEANER ON THE GASKET.

After you clean the solenoids I would just drive the car and see if the trouble code comes back. If it does come back, we can check the modulator fluid pressure valve.

[Tuner4Life]

Codes are inconsistent

I hooked everything back up and the codes are not consistent. Once again, they've gone away altogether and when codes do pop, they aren't the same ones.

[Tuner4Life]

gonna check the other readings now

Just noticed your new post. Going to check that now.

[AbsurdNY]

I hooked everything back up and the codes are not consistent. Once again, they've gone away altogether and when codes do pop, they aren't the same ones.

If you are getting more codes, it could be the TCU.
What are the other codes you are getting?

[Tuner4Life]

Other codes

Hard to tell to be honest. Indicator is too erratic when it flashes so I haven't been able to make another one out really. If I were to guess what it's showing I believe it's 11 which from what I can tell is a faulty ignition coil and that makes no sense at all.

[Tuner4Life]

Think I found the problem.

I pulled the TCU out and removed the cover. It's gotta capacitor leaking and a burned resistor. I do electronics for a living so i'm pretty sure that's a safe bet. Only question would be if that's a common issue with these and what causes it.

[Tuner4Life]

More damage

Looks like theres a cooked diode as well.

[AbsurdNY]

I pulled the TCU out and removed the cover. It's gotta capacitor leaking and a burned resistor. I do electronics for a living so i'm pretty sure that's a safe bet. Only question would be if that's a common issue with these and what causes it.

It is common for 3 things inside the TCU to burn out in these cars.
Here is a write up on some of the parts that fail in the TCU often:

Problem: The usual problem with the Honda Accord transmission, namely the 90,91, -, - Accord, is a bad transmission computer. What happens is that the transmission computer has a couple cheap parts that fail. The failing parts may or may not automatically put the TCU into a saftey (limp) mode (aka, the "fail safe strategy.") The three known failed components are two resistors and a capacitor inside the transmission computer. The symptoms are of several types. The car "S" light or "D4" is on (stuck on no matter what gear selection) or blinking and the transmission won't shift into any gears or sometimes stuck on a certain gear. The trouble codes could be 1,2,7,8,9,15 or None. Shifter interlock control unit buzzes. When the driver steps on the gas the rpm goes high but the car refuses to move at the expected speed. By resetting the TCU, either by the proper method or by disconnecting the negative battery for 5 to 10 seconds will eliminate the problem, but only temporarily.



Inferior resistors:
The resistors R41, R42, R43, are overheated or burned and capacitors C27, C28, C32, C33, C5 leaking or shorted. Some resistors will be burned off and we do not know the values. A common sense approach is to consult a working TCU and read the color code on the resistors or start with the highest resistance and go down. Find the best wattage resistor that can fit.



The problem originates with the electrolytic capacitors leaking. Often, the capacitor short circuits frying other components such as your resistor. Another words, the burned resistor is a result of another component failure, namely the capacitor. The fix is to replace the bad parts.

Parts values: R41 is most likely 15 Ohms; R42 is 15 Ohms, both appears to look like a 1/4 to 1/2 Watt; Capacitor C28 105`C 220uF 35V Nichicon H9146

[Tuner4Life]

Thx for all the help

I appreciate all the help, seems like a made a good choice coming to the CB7 community. Hopefully i'll get as good with these cars as I am with mustangs so I can help out others as well. I'll let you know what happens. Off to the pick-n-pull to see if they have what I need and maybe some spare parts to fix the TCU that fried as well just in case. Once again, thx for the help.