To check the sensor output, turn the DVOM to AC Volts. Rotate the wheel or whatever speed you are measuring. Place the meter leads across the sensor and measure the AC voltage output. Typically, if the shaft is rotated at about one turn every 2 seconds the output should be around.

A bad transmission speed sensor makes for rough and difficult gear changes, and can leave you without an accurate speedometer. All this adds up to a dangerous drive, worsened by the fact that your car is probably less efficient, and producing more harmful emissions.

Most Common Symptoms of a Faulty Engine Speed Sensor

1. Transmission revs higher before it changes gears.
2. The car’s transmission engages into overdrive late and sometimes will never go into that top gear.
3. Brakes are sometimes harder than normal when coasting.
4. Speedometer behaves erratically or sometimes does not work at all.

Unfortunately, it is impossible to repair the transmission speed sensor as it simply fails. You have to discard it and replace it with a new one. A professional mechanic should help you examine and diagnose the speed sensor system of your vehicle even though the symptoms may seem similar in all cars.

After an OBD II scan you learn that your input or output vehicle speed sensor (VSS) has malfunctioned and needs to be replaced. Depending on the vehicle year, make and model, a speed sensor can cost as little as $7.92 or as much as $100. For most vehicles, the cost for a speed sensor is between $25 and $45.

How to Troubleshoot Speed Sensors

1. 1.) Check Sensor Connection.
2. 2.) Check Gap.
3. 3.) Resistance Measurement (two wire plug only)
4. 4.) Check Power (three wire plug only)
5. 5.) Check Wiring (three wire plug only)

Since any engine requires the correct air to fuel ratio and ignition timing to start, having a faulty sensor that can’t adjust these symptoms on the fly can cause the engine to not start. Faulty sensors can keep your engine from starting, but this is often engineered in as a safety measure.