Jump to content

  • Welcome to Auto Parts Forum

    Whether you are a veteran automotive parts guru or just someone looking for some quick auto parts advice, register today and start a new topic in our forum. Registration is free and you can even sign up with social network platforms such as Facebook, Twitter, Google, and LinkedIn. 

     

Active vs. Passive Wheel-Speed Sensors


Recommended Posts

rssImage-6af6c4debce8e747cf303218a0029863.jpeg

Wheel-speed sensors aren’t new to any of us. They’ve been around for years, and their initial purpose was to provide wheel-speed data to the control unit for the antilock braking system (ABS). Because of this, they’re often called ABS sensors.

On today’s vehicles, however, the ABS isn’t the only system that utilizes wheel-speed data. Multiple safety and comfort systems such as advanced driver-assistance systems (ADAS), traction control and parallel-parking assist rely on wheel-speed data to function properly.

At a glance, all wheel-speed sensors may appear to be the same. But there are two different types: passive and active. Essentially, both have the same job of providing wheel-speed data to various control units, but they differ in how they do it and how well they do it.

Passive Wheel-Speed Sensors

Passive wheel-speed sensors are constructed with a permanent magnet and fine copper wire and generate a magnetic field. They operate in conjunction with a toothed metal ring, called a tone ring, which rotates at wheel speed. As the teeth of the tone ring pass through the magnetic field, it causes the polarity of the sensor to change and generates an alternating-current (AC) signal.

This AC signal is sent to the ABS control unit, which in turn must interpret it to determine when ABS operation is required. While passive sensors have been effective for many years, they have several drawbacks. A common problem with these and any type of permanent magnet sensor is limited operation at low speeds. In the case of wheel speed, a passive sensor is only able to generate a signal at approximately four miles per hour and higher.

They also do not generate a signal in reverse, and the gap between the sensor and the teeth on the tone ring is critical. Even the slightest amount of rust buildup underneath one of these sensors can cause erratic operation and unwanted activation of the ABS under braking. In addition, the magnetic field of these sensors can attract fine metal particles over time, which further inhibit proper system operation.

Active Wheel-Speed Sensors

The AC signal generated by a passive wheel-speed sensor is an analog wave, or a continuous smooth waveform. An active wheel-speed sensor, on the other hand, produces a digital signal, which is viewed as a square waveform. A digital signal is a very accurate and precise on/off signal.

Many of the other control units associated with today’s advanced systems rely on this type of precision for proper system operation. In addition to the accuracy, an active wheel-speed sensor can read wheel speed practically to zero mph, which is critical data for modern traction-control and driver-assistance systems, and some also can detect reverse wheel rotation.

Active wheel-speed sensors require power to operate, whereas passive units do not. There are two types of active wheel-speed sensors: a Hall-effect sensor and a magneto-resistive sensor. A Hall-effect sensor requires either a toothed or magnetic ring to generate a voltage signal, whereas a magneto-resistive sensor utilizes a slightly different type of encoder ring, allowing it to determine direction of wheel rotation.

The most important part about these sensors is knowing that they’re different. Visually they look the same, but functionally they’re not interchangeable. Some makes and models that are traditionally thought of as the “same” vehicle with different badging can utilize different sensors, even for the same model year.

When it’s all said and done, active wheel-speed sensors are necessary for today’s advanced systems, but regardless, all wheel-speed sensors take a lot of abuse, simply due to their location. Any time there’s a problem indicating a bad wheel-speed sensor, all components must be taken into account including the sensor itself, as well as the wheel bearing and CV joint, which may house or support the tone ring or encoder wheel necessary for sensor operation.

The post

link hidden, please login to view
appeared first on
link hidden, please login to view
.

link hidden, please login to view

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Similar Topics

    • By Counterman
      While it might not sound like it to the untrained ear, the orchestration of components to achieve the ideal combustion cycle is nothing short of a symphony.
      For fuel-injected engines, two important instruments in this precise arrangement are the mass airflow (MAF) sensor and the manifold absolute-pressure (MAP) sensor.
      The MAF sensor, typically situated between the air-filter housing and the intake manifold, might be considered the maestro. Also known as an air meter, the MAF sensor uses a heated element to measure the amount of air by weight that’s entering the engine. As the air cools the heated element, this cooling effect changes the electrical resistance of the element. The amount of cooling the element experiences is directly proportional to airflow, and the sensor conveys this information to the engine computer by way of changing voltages or digital frequencies.
      The engine computer then uses this information – along with other inputs – to adjust the amount of air entering the engine.
      Other inputs that help determine the proper air-fuel ratio include: oxygen sensors, which measure the amount of air in the exhaust gases; throttle-position sensors, which tell the computer if the throttle is closed, partially open or wide open; knock sensors, which monitor for signs of engine knocking; and (on some vehicles) MAP sensors, which measure the amount of pressure or vacuum in the intake manifold.
      While most fuel-injected engines today utilize a MAF sensor to obtain a precise measurement of airflow, MAP sensors play a starring role in fuel-injected vehicles with speed-density engine-management systems. However, turbocharged engines often have both a MAF and a MAP sensor.
      “In turbocharged engines, the partnership between MAP and MAF sensors isn’t just a technicality – it’s the secret behind the vehicle’s ability to harness forced induction with unparalleled precision,” Walker Products explains.
      Let’s take a closer look at each type of sensor and what they bring to the table.
      MAF Sensors
      Air changes its density based on temperature and pressure. In automotive applications, air density varies with the ambient temperature, humidity, altitude and the use of forced induction (turbochargers and superchargers). Compensating for changes in air density due to these factors is essential for maintaining the optimal air-fuel mixture and efficient engine operation.
      Consequently, MAF sensors are better-suited than volumetric-flow sensors to provide an accurate measurement of what the engine needs. MAF sensors offer a more direct and accurate measurement of the critical parameter for engine combustion: the mass of air. This facilitates better engine performance, fuel efficiency and emissions control compared to relying solely on volumetric-flow measurements.
      There are two types of MAF sensors used in automotive engines: the vane-meter sensor and the hot-wire sensor.
      The vane-type MAF was the first one out there, and it was used on import vehicles from the 1970s and 1980s.
      “It didn’t have many actual problems,” Charles Dumont explains
      link hidden, please login to view. “However, many of them were replaced, because back then the vehicles didn’t have onboard diagnostic capabilities. Usually after mechanics and DIYers had replaced all the other ignition parts and sensors, the MAF sensor was the last-ditch effort.” These days, you’re more likely to encounter the hot-wire style of MAF sensor. The hot-wire MAF sensor is smaller, faster and more accurate than the older vane-type MAF sensor, making it the preferred choice in most late-model vehicles.
      Delphi provides a great explanation of the hot-wire MAF sensor
      link hidden, please login to view. “Put simply, a MAF has two sensing wires,” Delphi explains. “One is heated by an electrical current, the other is not. As air flows across the heated wire, it cools down. When the temperature difference between the two sensing wires changes, the MAF sensor automatically increases or decreases the current to the heated wire to compensate. The current is then changed to a frequency or a voltage that is sent to the ECU and interpreted as air flow. The quantity of air entering the engine is adjusted accordingly.”
      MAF sensors are pretty dependable, but there are a few things that can undermine their performance.
      Any air or vacuum leaks downstream of the sensor can allow “unmetered” air to enter the engine. This includes loose fittings or clamps in the plumbing between the air-filter housing and throttle, as well as any vacuum leaks at the throttle body, intake manifold or vacuum-hose connections to the engine.
      Anything that contaminates the surface of the sensor also can hinder its ability to respond quickly and accurately to changes in airflow. This includes fuel varnish and dirt deposits as well as any debris that might get past or flake off the air filter itself.
      A frequent cause of MAF-sensor failure is directly related to the air filter. Low-quality or incorrectly installed air filters can allow paper particles or dirt to accumulate on the hot wire, effectively insulating it and affecting the reading of the sensor.
      Oil-soaked air filters also can have an effect on MAF-sensor operation, so it’s important to warn someone of this possibility if they’re installing a performance high-flow filter. In some cases, modified intake systems can cause increased air turbulence, which can affect the performance of the MAF sensor as well.
      A dirty MAF sensor can cause performance problems and, in some cases, trigger a diagnostic trouble code. You can recommend MAF-specific cleaners (any harsher solvents can ruin the sensor) and air filters as maintenance items before your customer spends the money on a replacement sensor.
      Symptoms of a failing MAF sensor could include rough idling or stalling; RPM fluctuations without driver input; and a decline in fuel economy and engine performance. A problem with the MAF sensor often triggers a “Check Engine” light.
      MAP Sensors
      As the name implies, the primary function of a manifold absolute-pressure sensor is to measure the pressure within the intake manifold of an engine (usually a fuel-injected engine). Essentially, a MAP sensor is measuring the barometric pressure – the atmospheric pressure that’s pressing down on earth. Barometric pressure is influenced by changes in elevation, air density and temperature.
      The pressure reading from a MAP sensor is an indicator of engine load, and it helps the engine computer calculate fuel injection for the optimal air-fuel mixture. The MAP sensor helps the engine adapt to different operating conditions, such as changes in altitude or driving up a steep incline, where air pressure can vary significantly.
      A MAP sensor contains a sealed chamber that uses a flexible silicon chip to divide the sensor vacuum from the intake-manifold vacuum. As soon as the driver starts the vehicle, the MAP sensor is called into action, performing “double duty as a barometric-pressure sensor,” according to Delphi. With the key turned on but prior to the engine starting, there’s no vacuum in the engine applied to the MAP sensor, so its signal to the engine computer “becomes a baro reading helpful in determining air density.” 
      “When you start the engine, pressure in the intake manifold decreases, creating a vacuum that is applied to the MAP sensor,” Delphi explains on its website. “When you press on the gas accelerator pedal, the pressure in the intake manifold increases, resulting in less vacuum. The differences in pressure will flex the chip upward into the sealed chamber, causing a resistance change to the voltage, which in turn tells the ECU to inject more fuel into the engine. When the accelerator pedal is released, the pressure in the intake manifold decreases, flexing the clip back to its idle state.”
      Typically, you’ll find the MAP sensor in the air cleaner, fender wall, firewall, intake manifold or under the dash, Standard Motor Products (SMP)
      link hidden, please login to view.  Given their location, MAP sensors commonly fail “due to the constant contact of the movable wiper arm over the sensor element and the exposure to the high underhood heat,” according to SMP. The high heat can melt or crack the electrical connectors. MAP sensors also are susceptible to contamination.
      “If the MAP sensor uses a hose, the hose can become clogged or leak and unable to read pressure changes,” Delphi explains. “In some cases, extreme vibrations from driving can loosen its connections and cause external damage.”
      A failing MAP sensor will compromise the engine’s ability to maintain the proper air-fuel ratio, leading to a number of potential symptoms. These symptoms could include noticeably poor fuel economy, sluggish acceleration and an odor of gasoline (signs of a rich air-fuel ratio); surging, stalling, hesitating, overheating and a general reduction in engine power (signs of a lean air-fuel ratio); higher emissions that can lead to a failed emissions test; erratic or unusually high idle; and hard starting or even a no-start condition. A faulty MAP sensor also can set off a “Check Engine” light.   
      Parting Thoughts
      MAF and MAP sensors are small components that play a big role in modern fuel-injected engines. With turbocharged engines becoming more and more prevalent in some of the most popular models on the road today, these sensors should continue to play an important role in automakers’ fuel-economy and emissions-control strategies.
      “As turbocharged technology evolves, understanding and optimizing the cooperative function of these sensors becomes the key to unlocking the full potential of modern turbocharged engines,” Walker Products explains.
      The post
      link hidden, please login to view appeared first on link hidden, please login to view.
      link hidden, please login to view
    • By Dorman Products
      Active Grille Shutters | Counterperson Training from Dorman Training Center
    • By Dorman Products
      Active Suspension Systems | Counterperson Training from Dorman Training Center
    • By Counterman
      Continental has added eight new part numbers to its line of OEM knock sensors.  
      The sensors are the same part that the vehicle manufacturer uses and deliver the exact fit, form and function as the original part, ensuring an easy installation and long service life, according to Continental.
      The eight new part numbers provide application coverage for some of the most popular domestic, European and Asian makes and models on the road today. The expanded line covers Chrysler, Dodge, Ford, Infiniti, Jeep, Lincoln, Mercedes-Benz, Mercury, Nissan and Ram models ranging from 2000 to 2023. The new sensors provide coverage for 28.8 million vehicles in operation (VIO) in the United States and 2.4 million vehicles in Canada.
      “Our newly expanded line was developed to meet the growing need for reliable knock sensors on some of the most common vehicles on the road today,” noted Brendan Bachant, Continental product manager for engine management and fuel. “The original sensors can be prone to failure due to mechanical damage, excessive vibration, high engine temperatures, and corrosion. Continental has made these OEM sensors available to the aftermarket so that professional technicians can easily and confidently service the most common vehicles in the shop, like the Ford F-150 and Explorer, the Jeep Wrangler and the Nissan Maxima and Altima. Technicians can be confident when choosing the Continental knock sensor that they will avoid comebacks.”
      Knock sensors are designed to detect engine ping caused by pre-ignition and relay the information to the electronic control unit to adjust engine timing and help keep the engine running smoothly. These sensors are an ideal repair for a rough-running engine with a timing and knock-sensor fault code and will help shops to restore the performance of their customers’ vehicles to OE specifications, according to Continental.
      Continental knock sensors are built in ISO-certified facilities to deliver the highest level of dependability, the company noted.
      The post
      link hidden, please login to view appeared first on link hidden, please login to view.
      link hidden, please login to view
    • A-premium Auto Parts:5% OFF with Code GM5.
    • By Counterman
      Older vehicles with carburetors and distributors didn’t need to know the position of the crankshaft or the camshaft. Timing was fixed, and the timing could easily be set, as long as the technician could line up top-dead-center on cylinder No. 1 and line up the mark on the crankshaft pulley. But this was back before fuel injection was standard, and today’s engines are a lot more advanced than those older carbureted engines.
      Today, the engine control unit (ECU) needs to monitor the exact position of the crankshaft and the camshaft (or camshafts) at all times. This is accomplished through the use of camshaft position sensors and crankshaft position sensors. The ECU uses the information from these sensors to adjust the timing of the valves, fuel injectors and ignition coils.
      Put simply, the ECU cannot accurately calculate ignition timing and VVT parameters without knowing precisely where the crankshaft and camshaft both are at any given moment. These sensors are critical to ensuring maximum efficiency, power and torque during all operating conditions.
      But what happens when these sensors start to fail, or fail completely? Individual experiences may vary, but you can expect to see symptoms such as:
      • Rough or erratic idle
      • Crank/no-start
      • Loss of power
      • Illuminated “Check Engine” light
      A faulty crankshaft position sensor can cause the engine to crank but not start, also known as a “crank/no-start.” The engine may be able to run without a signal from the camshaft position sensor, but it may trigger a reduced-power or “limp-home” mode.
      If your customer checks the ECU for DTCs and they find P0011 (camshaft position bank 1) or P0021 (camshaft position bank 2), their first step should be to check the engine oil. That’s right, check the engine-oil level, and top off as needed. Dirty oil, or a low oil level, can wreak havoc with the VVT components and cause these DTCs to set. In fact, the most common cause for VVT-system issues seems to stem from a lack of basic maintenance. Old, dirty oil can carry sludge and debris that can plug up the tiny passageways for the VVT actuators and other components.
      The relationship between the camshaft and crankshaft is critical in today’s VVT systems. If the camshaft sensor or crankshaft sensor starts to produce a faulty signal, the VVT-system performance will suffer. Of course, a loose or stretched timing chain or timing belt, or a worn timing guide or tensioner, also can negatively affect the VVT system.
      What causes a crankshaft or camshaft sensor to fail? While every electronic component under the hood will fail eventually, camshaft sensors and crankshaft sensors can fail prematurely if they’re subjected to extreme temperatures (i.e. engine overheating) and/or contamination (metal shavings or debris carried by the oil, or contamination from an outside source under the hood).
      So, now we know a bit more about the relationship between the camshaft position sensors and crankshaft position sensors and modern-day engine management. These days it’s safe to say that every vehicle system is sharing data, so they all depend on one another to operate at their best. In this case, data from the crankshaft sensor and camshaft sensor allows the ECU to optimize the timing of the valves, fuel injectors and the ignition coils. This continuous optimization enables modern engines to run with far greater efficiency than ever before.
      The post
      link hidden, please login to view appeared first on link hidden, please login to view.
      link hidden, please login to view

×
  • Create New...