3 Bad Transmission Speed Sensor Symptoms

What is the Transmission 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 transmission data to the vehicle’s powertrain control module. The first is known as the input shaft speed (ISS) sensor. As described, this sensor is used to monitor the speed of the transmission’s input shaft. The other sensor is the output shaft speed (OSS) sensor. If either of these two sensors falls out of alignment or experiences electrical issues, it impacts the operation of the entire transmission.

After registering data, the two transmission speed sensors, also commonly referred to as vehicle speed sensors (VSS), send data to the powertrain control module (PCM), which compares these two inputs and calculates which gear the transmission should engage 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. The lifetime of a transmission speed sensor can be up to 120,000 miles, but can fail at any time because of wiring issues, or simply from wear and tear if you drive your vehicle a lot.

Should either or both of these speed sensors fail, you may notice one or more of the 3 common transmission speed sensor symptoms listed below.

1. Harsh or Improper Shifting

The first symptom of a bad transmission speed sensor is 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 roughly or more quickly 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 shift smoothly. When the transmission shifts hard, it can damage internal components including valve bodies, hydraulic lines, and in some cases mechanical gears. If you notice 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

Another symptom of a bad speed sensor is when the cruise control stops working. Since the transmission speed sensors monitor the input and output shaft speed, it also plays a part in monitoring the cruise control. When the transmission 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 and you may need a cruise control speed sensor replacement.

3. Check Engine Light Comes On

The final symptom of a speed sensor problem is if the Check Engine Light comes on. If the signals are lost from the transmission speed sensors, the PCM will set a DTC and illuminate the Check Engine Light on the vehicle dashboard. It also can indicate an increase in tailpipe emissions surpassing acceptable limits for environmental contaminants from motor vehicles.

If you notice any of these symptoms, you may need to replace the transmission speed sensor. In any case, if you notice that the Check Engine Light comes on, you should contact a local mechanic to scan 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, a professional certified mechanic 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.


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Recent Transmission Speed Sensor Replacement reviews

Excellent Rating

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Rating Summary
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Bobby

28 years of experience
88 reviews
Bobby
28 years of experience
Dodge Durango V6-3.7L - Transmission Speed Sensor - Charlotte, North Carolina
He was on time kind and very knowledgeable he is a really good mechanic and had a game plan already when he arrived Mr.Bobby was more than I expected 👍
Lexus GS300 - Transmission Speed Sensor - Charlotte, North Carolina
Bobby arrived early, called and confirmed the appointment, explained all of the services and he was courteous, professional, honest and his integrity was much appreciated.

John

33 years of experience
1126 reviews
John
33 years of experience
Land Rover LR3 V8-4.4L - Transmission Speed Sensor - Galveston, Texas
John was very professional and experienced in fixing cars. I made the mistake of diagnosing the problem and the part, I was wrong. I highly recommend having John diagnose the problem with the car first visit and taking his advice on the next steps to fixing the car or truck. I rated John four stars because he did an outstanding job of helping me with a 2008 LR3 with over 200K miles. These cars are high$$$ maintenance and the extent of the work needed to be done is best spent and placed into a trade-in on a new car.
Chrysler Sebring - Transmission Speed Sensor - Bacliff, Texas
Great service , arrived on time with everything needed. I will be using him in the future.

Andrew

26 years of experience
150 reviews
Andrew
26 years of experience
Dodge Ram 1500 V8-5.2L - Transmission Speed Sensor - Monroe, Georgia
Andrew was great, professional, courteous and very helpful. I would definitely recommend to my friends
Lexus IS300 - Transmission Speed Sensor - Jonesboro, Georgia
Mr. Elphic was very professional. He called and asked if he could arrive sooner than expected, which was definitely a plus. Upon arrival, he confirmed the services he would be performing and I supplied the parts. He finished in a very timely manner and communicated other repairs needed in the near future. All old parts were given back to me boxed up and the area was clean as if he never performed any work. I was skeptical of using this online service but I wish i had known about it sooner. The price was outstanding and the work is excellent. There's no hassle and no up-selling. Mr. Elphic was very friendly and professional and I'm definitely going to use this service from now on. I can't imagine ever going to a garage/shop again, unless it's something major.

Brandon

19 years of experience
275 reviews
Brandon
19 years of experience
Dodge Ram 1500 V8-5.2L - Transmission Speed Sensor - Stone Mountain, Georgia
Very quick and was able to diagnose another problem just by listening to the engine. I think Brandon is a great mechanic.
Chrysler Town & Country - Transmission Speed Sensor - Hoschton, Georgia
Brandon is very knowledgeable, HONEST, and a TRUE professional. A well-known "Christian", family-owned since 1961 transmission SPECIALIST quoted us $4500 for a brand new tranny in a vehicle with 97,000 miles on it as their ONLY solution AND after their suggested tow operator charged me $90 to go 9 miles. Ended up being an $18 senor which Brandon replaced and saved me literally THOUSANDS of dollars. I will recommend ypurmechanic.com to EVERYONE I know. From the customer service rep when I initially booked the appointment, to their confirmation and follow-up, to the service provided by Brandon.... "This one goes to 11"...!!!

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