The D4 light flashes and the speedometer goes back and forth while driving what causes this

is the speedo connected ??

If the D4 light is flashing, you have a transmission control failure and you need to get your transmission and transmission control system checked out.

engine check light does come on if your VSS doesn't work.
i suggest you use a car diagnostic tool check your car.
mvci honda toyota have a look.

The D4 light is coming on to tell you that there is one or more fault codes set in your transmission control module. The only way to retrieve codes on the 1995 models is to read "Flash Codes" output by the D4 light. (See instructions below)

RETRIEVING FLASH CODES USING THE D4 LIGHT
If fault codes are present, the D4 light will "blink" when the ignition is turned to the RUN position and will remain on at all times when the engine is running.
To retrieve the flash codes, turn the ignition switch off.
Install a jumper wire between the service check connector terminals.
The service check connector is a gray, 2-pin connector located on the PCM/TCM cover under the passenger side of the instrument panel. (See picture below)

CAUTION: DO NOT use the 3-pin located next to the service check connector.

Installing the jumper will place the PCM/TCM in diagnostic test mode.
Turn the ignition to the RUN position. Codes will be output by blinking the D4 light.
Note the number of blinks from the D4 light. A short blink indicates a single digit flash code. A long blink equals 10 short blinks. For instance one short blink indicates code 1. One long blink and four short blinks indicates code 14. If there is more than one fault code, they will be output one at a time from the lowest numbered code to the highest numbered code. It is recommended that you read the code or codes several times to make sure that you are reading it correctly.

Once you have retrieved the fault code(s) re-post your question and include the information for what codes you have and someone can then help you locate the cause of the problem.

could be speed sensor. the light is on because the trans doenst know the vehicle speed.

Hi, a few questions 1st. Did your mechanic check for engine codes? Is your Honda a v-6 or 4 cylinder?
The flashing D4 light indicates a possible transmission malfunction. You should avoid rapid acceleration until the cause of the light blinking is determined.
If you have the V-6, there is a diagnostic port to connect a scan tool to read any stored engine codes that have turned on the check engine light. This port is located behind the ashtray in the center console (most cars did not have this til 96).
If you have the 4 cyl engine, there is a service connector located under the dash on the pass. side. Inside the connector is what looks like a 2 wire plug should be attached. Take a paper clip, unbend it, and insert the 2 ends of the clip into the connector to 'jump' it. Turn the ignition switch to the on position (don't start the vehicle), and the check engine light will flash. Count the flashes, short flashes are for code #'s 1 to 9 (single digit code), a 2 digit code will be a long flash for the 1st digit, followed by a short flash for the 2nd digit. If there is more than one code, they will be separated by a pause. They will repeat so you can count them and write them down. Let me know what the code #'s are so I can help further. Curt

When the D4 light flashes that is an indication of a problem with the transmission. You need a speed sensor located on the transmission make sure to get the electrical part ths will solve BOTH problems.

The transmission control unit has gone bad, a very common problem. There is a capacitor in the TCU that goes bad and cause a short on the board. Do not get a used one, they are all bad. A number of people sell rebuilts on Ebay. The TCU is under the Front passengers feet, pull back the carpet and you'll see both the PCM and TCU.

google "accord tcu" or "tcm" if you like

Need more info, just ask
Dave

this sounds like a Transmission Speed Sensor. ive done about 20 of them , common on hondas

on my 95 accord my d4 light used to flash after driving for for an hour or 2 then the speedo would do strange things.so i changed the speed sensor relay [located on the gearbox] and solved the problem.