Skip the auto shop - Our mechanics make house calls
  1. Home
  2. Articles
  3. Symptoms of a Bad or Failing Speed Sensor

Symptoms of a Bad or Failing Speed Sensor

The transmission speed sensors are used to calculate the actual gear ratio of the transmission while in use. There are generally two speed sensors that work in conjunction to provide accurate data to the vehicle’s onboard computer. The first transmission speed sensor is known as the Input Shaft Speed (ISS) sensor. As described, this sensor is used to monitor the speed of the transmission' input shaft. The other sensor is the Output Shaft Speed (OSS) sensor. When any of these two sensors falls out of alignment or experiences electrical issues, it impacts the operation of the entire transmission speed sensor.

After registering data, the two transmission speed sensors, also commonly referred to as a vehicle speed sensor (VSS), send data to the Powertrain Control Module (PCM); which compares these two inputs and calculates which gear the transmission should be engaged for efficient driving. The actual gear ratio is then compared to the desired gear ratio. If the desired gear and the actual gear do not match, then the PCM will set a diagnostic trouble code (DTC) and illuminate the Check Engine Light or Malfunction Indicator Lamp (MIL).

Should either or both of these speed sensors fail, you may notice one or more of the following issues.

1. Harsh or improper shifting

Without a valid speed signal from these sensors, the PCM will not be able to correctly control the shifting of gears within the transmission. This may cause the transmission to shift rough or quicker than normal. It's also common that a problem with these sensors can impact the shift timing, extending the interval between transmission shifts. An automatic transmission is hydraulically controlled and designed to operate smooth. When the transmission shifts hard, it can damage internal components including valve bodies, hydraulic lines and in some cases, mechanical gears. If you notice that your transmission is shifting harshly or roughly, you should contact a local ASE certified mechanic as soon as possible.

2. Cruise control does not work

Since the transmission speed sensors monitor the input and output shaft speed, it also has a hand in monitoring the cruise control. When the sensors fail to deliver accurate data to the onboard computer on your car, truck, or SUV, the powertrain control module (PCM) will send an error code to the vehicle’s ECU. As a safety precaution, the ECU will shut down the cruise control and render it inactive. If you notice that your cruise control does not engage when you press the button, contact a mechanic so they can inspect the vehicle and determine why the cruise control is not working. It may be due to faulty transmission speed sensors.

3. Check Engine Light comes on

If the signals are lost from these sensors, the PCM will set a diagnostic trouble code (DTC) and illuminate the Check Engine Light on the vehicle dashboard. This alerts the driver to an issue that should be investigated quickly because an error code has been sent to the vehicle's computer. It also can indicate that there is an increase in tailpipe emissions is occurring that surpasses acceptable limits for atmospheric contaminants from motor vehicles.

In any case, if you notice that the Check Engine Light comes on, you should contact a local mechanic to download the error codes and determine why the Check Engine Light is illuminated. Once the problem has been fixed, the mechanic will reset the error codes.

If the problem rests with the speed sensors, depending on your particular transmission, the professional ASE certified mechanics from YourMechanic.com may be able to replace the sensor. Some speed sensors are internal to the transmission and will require the transmission to be removed from the vehicle before the sensors can be replaced.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
Still not sure about your car's issue?
Diagnose your car
What kind of issue are you experiencing?
Brakes are squeaking
Car is not starting
Car is overheating
Car is shaking (vibrating)
Fluids are leaking
Heating and A/C
Smoke or steam is coming out of the car
Warning light is on
Icon-warranty_badge-02

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

More related articles

P0222 OBD-II Trouble Code: Throttle/Pedal Position Switch/Sensor B Circuit Low Input
P0222 code definition Throttle/Pedal Position Switch/Sensor B Circuit Low Input What the P0222...
How to Transfer a Car Title in Idaho
In order to prove ownership of a car, you must have the title. However, when a car is sold, given away or inherited, the title needs...
P2422 OBD-II Trouble Code: Evaporative Emissions Control System (EVAP) Vent Valve Stuck Closed
Diagnostic Trouble Code (DTC): P2422 P2422 code definition Evaporative Emissions Control System (EVAP)...


Related questions

Q: Hesitation, stumbles, and sometimes stalls when accelerating

Hi there, thanks for writing in. It looks as if you've covered almost all of the bases. The only thing that I could think of without being there to complete a diagnostic inspection is that perhaps the idle control valve...

Q: Where is temperature sensor

The engine coolant temperature sensor should be located on the radiator hose fitting on the front of the engine. The connector is locked in place by a clip lock on the connector housing that needs to be depressed at the...

Q: serious issue with my right rear brake.

Yes, I agree this is a serious issue. If the hub bearing failed, the tire and brake assembly would be loose. To check this, raise that part of car off the ground, put hands on each side of the tire...