Symptoms of a Faulty Speed Sensor in Your Vehicle

The speed sensor in your car performs a variety of tasks, from telling you how fast you are going, to directing a vehicle with automatic transmission when to change gears. When this sensor malfunctions, the result can be a vehicle that is acting strangely.

Faulty Speed Sensor Symptoms

If you are trying to figure out whether the speed sensor in your car is working or not, here are 5 common symptoms of a failing speed sensor.

1. Cruise Control Doesn’t Work

Since the speed sensor is responsible for establishing how fast the car is going, cruise control won’t work properly if it is faulty. Fortunately, this doesn’t mean an out of control car going too fast, or a car that slows down to a stop. Instead, when the vehicle senses the speed sensor is malfunctioning, it sends an error code that disables cruise control completely. Even if you haven’t read the codes, if you notice cruise control no longer works it is a big clue that your speed sensor is either failing or completely nonfunctional.

2. Your Check Engine Light Is On

When the vehicle detects any error inside the engine, the check engine light is triggered. Since the check engine light can be from any error detected by the engine, this does not necessarily mean it is the speed sensor. If the check engine light comes on, pulling the codes can help you confirm whether it is the speed sensor or not.

3. Timing Of The Shift Is Slower

Another common symptom of a failed or failing speed senser is that shifting gears in an automatic will be difficult. The transmission relies on input from the speed sensor in order to decide when to shift, and if it isn’t working properly the speed sensor may have difficulty choosing when to shift.
You may also notice the engine running rougher as the vehicle struggles to shift, or sound off when idling. This is another common symptom that could help you confirm that the speed sensor is your issue.

4. Your Speedometer Is Not Working

A slightly more obvious symptom is when the speedometer isn’t working properly. This doesn’t have to mean that your speedometer has quit working completely, it could simply fail to work properly, and then other times behave as if nothing was ever wrong.
This may make you feel like you’re going crazy, but it could also be your speed senser acting up.

If you notice all or some of these symptoms, a bad speed sensor could be the problem. To confirm the problem, it’s best to get a computer diagnostic on your car. The diagnostic can check for transmission problems, which can behave in a similar way to a speed sensor issue.

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If it is a speed sensor, replacing it may be difficult depending on the location of the failed sensor. Some speed sensors are inside of the transmission itself, and require the transmission to be completely removed in order to replace it.

How Long Can You Drive a Car with a Bad Speed Sensor

Every vehicle has two-speed sensors: the transmission speed sensor and engine speed sensor. The former tracks the speed in which your vehicle is moving on the road, and the latter tracks the number of revolutions per minute of the crankshaft in your engine.

On the dashboard of your vehicle, there are two meters which show you the information coming from each sensor. The speedometer gives you the transmission speed coming from the transmission speed sensor, and the tachometer gives you the engine speed (RPM) coming from the engine speed sensor. The engine control unit receives this information as well. That way, the unit can manage the transmission and engine accordingly.

If you have a bad speed sensor in either case, then you can still drive your car indefinitely. This means you can operate your vehicle by driving it where you want to go, but you may experience some limitations with certain features. For instance, a bad transmission speed sensor will give you a faulty reading on the speedometer, and a bad engine speed sensor will give you a faulty reading on your tachometer.

As a result, you won’t know how fast your vehicle is moving or how fast your engine is running. You can’t survive very long on the streets like this, especially if you have to worry about speed limits and things like that. You need to know how fast you’re driving if you want to obey the law. Now you might not think that knowing the engine speed is any big deal, but that can indicate whether the engine is having a problem or not.

The biggest problem relates to how the engine control unit reacts to the bad speed sensor. Since each speed sensor communicates with the engine control unit, a faulty sensor could affect how the control unit manages the operation of the vehicle. Some of the common symptoms associated with bad speed sensors include a malfunctioning cruise control system, longer shift intervals, problems shifting and the check engine warning light coming on.

You can still drive your vehicle while dealing with these issues, but it’ll be more difficult. The best advice would be to drive at a steady pace until you can get your vehicle to an auto mechanic and have the faulty speed sensor replaced.

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