Question about 1990 Honda Civic
To know how to check the speed sensor please read the below explanation on how it works ad how it should be checked.
HOW IT WORKS
The Vehicle Speed Sensor (VSS) is a variable reluctance sensor that generates a sine wave type waveform with a frequency that is proportional to the speed of the vehicle.It has a gear on it that meshes into either the transmission/transaxle or the differential.
When the vehicle is moving slowly, the sensor produces a low frequency signal. As the vehicle speed increases, the sensor produces a higher frequency signal. This signal is sent to the PCM and is converted into a vehicle speed value, stored in RAM memory. The PCM utilizes this value to aid in controlling torque converter lock-up/transmission/transaxle shift points, control fuel injection, ignition timing and , coolant fan control, vehicle speed control, air/fuel ratio and ignition timing.
HOW TO CHECK SENSOR:
One way is to remove it from the tailshaft of the transmission or the differential housing (depends on vehicle)and hook the two leads to a volt meter on the AC scale or if you have a digital meter with a frequency scale you can use that too. This will measure the frequency in HERTZ (Hz.),meaning cycles per second. Spin the little gear(probably nylon)as fast as you can by hand (drag your hand /arm across it real fast like you were winding up a toy car or top)and watch the voltmeter for a reading. If you get a reading ( a few volts or Hz.) it's probably still functioning. You could also turn the gear with a variable speed drill.Keep it slow to be on the safe side.I'm guessing under 1000 RPM (most variables top out at 1250rpm for 1/2" and 2250rpm for 3/8"). If it won't go in the drill chuck (some gears have a little nub on the end you can grab),then wrap the gear with some tape and press the gear onto the side of the chuck,sort of like a bicycle generator on a bike tire.The tape will protect the little gear and help increase the friction between the two so it spins easily.
Another way is to leave the sensor in place, jack up the vehicle,drive wheels off the ground and turn the drive wheels by hand with your test apparatus hooked up to the leads on the sensor for similar results. The main thing is that you get varied voltages/frequencies at different speeds.If you get nothing it's busted. I DO NOT recommend that you run the vehicle while it is jacked up. Spinning the wheels by hand will tell you all you need to know.
Posted on Nov 19, 2009
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Posted on Jan 02, 2017
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