7 Symptoms of a Bad Speed Sensor
Modern fuel injected engines have many sensors working together to tell the engine and transmission computers what’s going on in the world. The computers need to know how fast the wheels are spinning, how fast the engine is spinning, and make sure all monitored parameters are within spec.
“Speed sensor” can refer to many different types of sensor. Some cars are equipped with wheel speed sensors, most cars are equipped with engine and transmission speed sensors, and some cars are equipped with all of the above.
But what happens when one of these speed sensors fails? Learn the most common symptoms of a bad speed sensor and how much it costs to replace one.
Symptoms of a Failed Engine Speed Sensor
1) Starting Problems (Problems Starting Your Car)
The engine speed sensor is often a critical part of vehicle control. If the ECU doesn’t know the position of the crankshaft or camshaft, it doesn’t know when to fire the spark plugs. A faulty crankshaft or camshaft position sensor can prevent your car from starting.
2) Check Engine Light
Some vehicles have redundant sensors that allow the vehicle to start and run even if the speed sensor fails. In these cases, you may see a check engine light with a code that gives you a clue as to which speed sensor is bad. The check engine light can be read for free at most auto parts stores, but you can also find inexpensive code scanners that you can use at home if you prefer.
Symptoms of a Bad Transmission Speed Sensor
1) Broken Speedometer or Odometer (How Many Miles Longer Will My Car Last?)
If this speed sensor fails, the speedometer may stop working. Some odometers may stop working because they use the same sensor as the speedometer. 2) Slow or hard shifts (dual clutch transmissions with paddle shifters)
Without a speed sensor, the transmission control unit (TCU) may have a hard time knowing when and how fast to shift. You may experience hard shifts or no shifts at all.
3) No cruise control
Cruise control needs information about the vehicle’s speed to function properly. If the speed sensor fails, cruise control may be unavailable until the sensor is repaired.
Symptoms of a Bad Wheel Speed Sensor
1) ABS Light (ABS Light On)
On vehicles equipped with ABS, the ABS light will come on if the wheel speed sensor is faulty. Most ABS systems will not function properly without a good signal from all four wheel speed sensors.
If the ABS light is on, don’t expect the ABS system to help you out if you need to brake suddenly. It’s best to resolve this issue immediately so you can regain full control of your vehicle during hard braking.
2) Traction or Stability Control Light (Traction Control Light On)
In addition to the ABS light, the traction and stability control lights may also come on. Ford owners may see a “Service AdvanceTrac” message. Without proper information from each wheel, the ECU may not have enough data to determine the relative speed between the driven wheels.
Cost to replace a speed sensor
Engine and transmission speed sensors
The cost of engine and transmission speed sensors varies depending on the type of sensor. A crankshaft or camshaft position sensor can cost anywhere from $30 to $250. Replacement parts are usually less expensive. A transmission speed sensor usually costs about the same.
Wheel Speed Sensors
Wheel speed sensors are generally very easy to access and replace. These sensors are relatively inexpensive to purchase as standalone parts, ranging from $30 to $200. Fortunately, most vehicles are at the lower end of this scale.
If your ABS sensor is built into the hub assembly, you can expect to pay a small fee for both the entire hub assembly and the installation labor. The hub assembly will cost about $200, and labor will be about $200 as well.
What is an Engine Speed Sensor? (Faulty Crankshaft Position Sensor)
There are many different types of engine speed sensors, but they all serve the same purpose: to tell the ECU where the crankshaft and camshaft are at all times.
The engine speed sensor is sometimes called a crankshaft position sensor, camshaft position sensor, crankshaft/camshaft angle sensor (CAS), or engine position sensor.
Engine management is important for proper combustion. The ECU needs to know exactly when to inject fuel and open valves to ignite the mixture to ensure optimal combustion. If this process isn’t perfectly synchronized, the engine won’t run properly, if at all.
Depending on the engine design, your car may have separate sensors for crankshaft position and camshaft position, or it may have just one sensor that performs both tasks.
Types of Crankshaft Position Sensors (Crankshaft Position Sensor Replacement Cost)
There are several common types of crankshaft position sensors. These sensors typically use electromagnetic or optical sensors that don’t require contact between moving parts. Because no moving parts come into contact with each other, these sensors typically do not suffer from wear and tear and have a long lifespan.
Magnetic Resistance Sensors
Reluctance sensors, also known as variable reluctance sensors, VR sensors, or magnetic sensors, resemble an electric guitar or bass pickup. They use a magnet wrapped around a coil of wire.
Reluctance sensors output a voltage when ferrous metal passes the sensor on a toothed trigger wheel, creating a current in a coil of wire inside the sensor. These sensors create a sinusoidal signal as the metal moves toward or away from the coil. Hall Effect Sensors
The crankshaft angle sensor (CAS) in early 1.8L Mazda Miatas is a good example of a Hall effect sensor. This sensor served a dual function.
Optical Sensor
Optical sensors use light passing through a rotating disc to measure speed. Like Hall Effect sensors, optical sensors also produce a square waveform. First generation 1.6 L Miatas used optical CAS sensors instead of Hall Effect sensors.
What is a Transmission Speed Sensor?
The transmission speed sensor communicates with the ECU or TCU to tell the automatic transmission what gear to be in. There are two main types of transmission speed sensors: input shaft speed sensor and output shaft speed sensor.
Input Shaft Speed Sensor
The input shaft speed sensor measures the speed of the input shaft and torque converter, which corresponds to the speed of the engine.
Output Shaft Speed Sensor
The output shaft speed sensor monitors the speed of the rear of the transmission after the transmission gear ratio has been applied. This is used to determine the vehicle’s traveling speed by the speedometer or odometer.
What is a wheel speed sensor? Wheel speed sensors can perform multiple tasks, including ABS functions, traction control, stability control, ground speed (speedometer and odometer), and tire pressure monitoring. If the ECU detects a difference in one or more wheel speed sensors, it can use that data to determine what is happening in that area.