This regards my 1994 Civic Coupe with D15B7 engine and manual tranny...located in Jamaica with few to assist, knowing I stand alone here as there aren't many of this model and the parts are rare here. Luckily I am stateside regularly.

About 2 years ago the speedo began being intermittently jumpy then finally stopped dead. I bought a used sender from an EX, installed it but had to change the connector to match the replacement and cleanup the wiring, which I concluded to be the main issue as I later swapped the old back in and worked also. I know this is an electronically driven speedo circuit as opposed to older cable type.. I worked fine but would still jump irregularly. I also know it is part of the ECU input sensors as well as driving the meter. It eventually stopped working altogether even after another pickup replacement. The main difference between previous failure and this is that it never showed any life at all after going dead.
I assume there is a wiring issue somewhere but have not found any diagrams I can use to trace the circuitry.
Can I make a new harness to bypass the current wiring after getting a diagram of the circuit.
Where might I find this circuit diagram, I know there are three wires originating at the hall sensor pickup, is there a way to test the sensor of board the car to verify they are working, then I can proceed from there and trace the circuit back to ECU and meter. I have the needed equipment and knowledge to do so with a little guidance from you very helpful guys.

 

You can back probe at the computer, but you must be sure of what you're doing to avoid frying it. Here's one way:


It's a paid channel with a free trial. Well worth the money either way.

 

The system is real simple. The three wires at the sensor are power (12 volts switched with the ignition), ground, and a pulse signal. Every few feet that the car moves generates a pulse. The speedometer looks at the rate of pulses, meanwhile the odometer uses the pulses to drive a stepper motor connected to the dials. The ECU also receives these pulses for some internal function but it is just teed into the line, it does not drive the reading on the speedometer.

When the car is moving, watch if the odometer rolls forward like it should. That would prove that the sensor is working and the problem is the speedometer head itself. It contains a circuit board that can suffer broken solder, leaky electrolytic capacitors, etc.

 

Sounds like a bad gauge. 94

 

FCM: Oops, I neglected to mention I bought a replacement panel as my tach had also died. Although a used working unit from US model, which appeared the same and all gauges and meters worked. I also replaced all the bulbs with LEDs except the CEL bulb which did not work with a LED and stayed lit, which I attributed to resistive load versus almost no load by LED, but all others look great. The CEL is working properly as indicated in another thread of min. Recal of my fuel gauge reading was necessary by repositioning of the sender unit variable resistor.

mk378: Very useful info as now I know what I can work out, especially a wire directly to the meter and drive the unit with a variable drill for stationary testing.

civicservice: I will watch that video and report back anything helpful...Thanks.

 

I've had to "rebuild" the electronic speedometers in three of my friends' early 1990's Toyota trucks. It is reaching the age where the capacitors are going to leak.

Remove the panel from the car. Carefully separate the clear plastic face from the rest. Unscrew the screws from the back (note that these screws make an electrical connection, so if they have become loose the speedo will stop working) and take the speedometer unit out. Inspect the circuit board and replace capacitors and repair traces as needed.