AfterMarketNews Auto Care Pro AutoProJobs Auto-Video.com Brake&Frontend BodyShopBusiness Counterman EngineBuilder Fleet Equipment ImportCar Motorcycle & Powersports News Servicio Automotriz Shop Owner Tire Review Tech Shop Tomorrow's Tech Underhood Service

The Problem With Living In The 'Now'

I once had a shop manager who concentrated on the “now.” Every day was a mad dash to complete the jobs at hand. He wanted to know who was working on what, where the parts were and when everything would be done. He was constantly reacting to a customer’s...

Read more...

ASE G1: Drive Belt Inspection, Replacement

The ASE G1 Certification test contains 55 scored questions, plus 10 unscored ­research questions, that cover a range of skills and knowledge related to maintenance and light repairs in engine systems, automatic transmission/transaxle, manual drivetrain...

Read more...

Amateurs and Hacks Provide Job Security For Automotive Service Professionals

Two cars pull up in front of my shop. The drivers didn’t come in, but I heard the commotion from my office window. The boyfriend opens the hood of his girlfriend’s car. They both stare at the engine; she tells the boyfriend that she was supposed...

Read more...

Acura: Clunk Noise While Turning

Model: Acura RSX 2005-’06 Symptom: The front suspension makes a ­clunking noise while turning. Probable Cause: The front springs are moving on the spring seats. Corrective Action: Replace both front springs and do a four­-wheel alignment. Diagnosis:...

Read more...

Inside Import Car Collision Warning, Automatic Braking Systems

Anything that moves under its own power also has to stop, so brakes have been a safety feature on cars since day one. Over the years, technical innovations such as antilock brakes (ABS) have ­improved the ability to stop with minimal skidding on...

Read more...

Intermittent Engine Misfire Analysis

Even for an experienced diagnostic technician, ­attempting to diagnose an intermittent misfire ­condition that occurs only under specific driving conditions can be a frustrating exercise. Let’s begin by getting the basics out of the way. As we know,...

Read more...

Analyzing the Cylinder Pressure Waveform from a Running Engine, Part 3

By Vasyl Postolovskyi and Olle Gladso Contributing Writers and Instructors at Riverland Technical and Community College in Albert Lea, MN   In Part 1 of this Maximizing Tools series, we discussed an alternative approach to diagnosing an engine...

Read more...

Mac Tools Is Wrenching for a Cure

In support of Breast Cancer Awareness month, Mac Tools is featuring a variety of Wrenching For A Cure products available for purchase in the Flyer 11 through Nov. 2. Featured pink products include clothing, accessories, flashlights, pint glasses, and...

Read more...

5 Tool Storage Tips

  As a technician, you likely own thousands of dollars worth of tools and equipment, and require tool storage capacity to hold them all, along with carts and accessories to help move those tools around your work area. Here are a few items...

Read more...

Battery Service and Diagnosis

A good battery with an adequate charge is absolutely essential for reliable cold starting. A weak battery, or one that is rundown, may not deliver enough amps to crank the engine when temperatures plunge and the oil thickens. Cold weather can be hard...

Read more...

Toughest Spark Plug Changes

We have all been there before: scratched arms, busted knuckles and an aching back caused by a difficult spark plug replacement job. If you think they are getting tougher every year, you are right. Every new engine design is putting the plugs deeper...

Read more...

Improving the Head Gaskets, Fasteners Relationship

The relationship between head gaskets and head bolts is an intimate one. The clamping load applied by the head bolts is what allows the head gasket to maintain its seal. For this marriage to last, there has to be constant tension – not too much,...

Read more...

Home Brakes Wheel Speed Sensors: ABS and TCS Signal Use

Print Print Email Email

Data from the scan tool provides information from the BCM as it processes the speed signal. Other sensors involved in the activation of the ABS system are the yaw, lateral acceleration and steering wheel position sensors.

A signal from the sensor can contain errors based on the condition of the reluctor or magnetic ring. Signal problems can cause the system to activate when it is not needed or set Diagnostic Trouble Codes (DTC). Information stored in the controller, called algorithms, is used to detect signal problems as well as a circuit open, short and/or ground.

Most vehicles in use today use two types of wheel speed sensors — variable reluctance and magnetoresistive. The wheel speed sensors’ input is key to the operation of the Electronic Stability Control (ESC) and Traction Control (TC) programming that can activate the ABS system and override the Electronic Throttle Control (ETC). The ESC, TC and ETC are programs that are located in different controllers that share information on the Controller Area Network (CAN) buss. This sharing of data input between controllers can produce problems and DTC that may appear to be unrelated to a WSS input. A scan tool is your resource to the operation of the CAN buss.

Sensor Types

Variable Reluctance
The variable-reluctance magnetic sensor has a permanent magnet pickup core and coil surrounding the magnet. The sensor is mounted at a specific gap from a notch-and-tooth reluctor ring. The rotation of the reluctor ring increases and decreases the magnetic field between the notch and the tooth to generate a voltage in the coil. As the gap between the notch and the ring changes with the rotation of the reluctor, the sensor generates an analog sine wave voltage signal. The voltage signal will increase in amplitude with an increase with the speed of the reluctor ring. The change in amplitude can affect the switching toggle in the BCM where a cracked reluctor ring may produce an extra switching toggle. The variable-reluctance sensor is a two-wire sensor mounted in the steering knuckle and rear suspension or axle.

Magnetoresistive
A Magnetoresistive sensor has a sensing element that contains an output module mounted on a silicon substrate and magnetic material. The magnetoresistive sensor’s main advantage is the ability to sense direction and operate with a wide air gap. The sensor is more stable in high vibration conditions and operates more efficiently than the reluctance sensor.

The sensor can detect the direction of rotation of the reluctor ring and zero speed. The sensor’s compact size can allow it to be incorporated into a hub bearing utilizing a alternating magnetic pole reluctor ring that is built into the rubber seal. A magnetoresistive sensor can be a two- or three-wire sensor. The three-wire sensor has a power, ground and signal connector pin.

The two-wire sensor has a power and signal connector pin. The ground is a part of the mounting for the sensor. The Philips magnetoresistive wheel speed sensor power input can range from 12 to 5 volts from the ABS controller.

The sensor produces a square wave signal with a high signal of 1.93 Volts, and a low signal of 0.64 Volts. The high signal must cross 1.29 Volts and the low signal must cross 0.97 Volts to low. The main advantage is that the amplitude of the signal does not change.

Diagnostic Procedures

The diagnosis of a trouble code or problem condition requires an investment in information and tools. The information and scan tool are expensive and are a good reason to charge for diagnostics. Diagnosing a DTC or failure condition should be performed in the following order. Technical Service Bulletins (TSB) search from your information data base. The condition may already exist and there is a known fix that can save time and money.

Scan Tool Retrieval of Diagnostic Trouble Codes and Data

The scan tool is the most efficient tool for diagnosing ABS sensor problems. If you are servicing three and four year old vehicles, your shop cannot function well without it. A Digital Volt Meter (DVM) and oscilloscope are used to verify a DTC or problem. An oscilloscope is the ultimate DVM. It measures voltage and time and many scan tools have a built-in scope. You can survive without a scope, but you have to have a good DVM that can measure frequency. Frequency can provide information that a signal is present.

Oscilloscope
The use of an oscilloscope can be a time consuming process that requires a certain amount of information to accurately display a wheel speed sensor wave pattern.

The following contains information for setting up an oscilloscope. The average automotive tire ranges from 24 to 28 inches in diameter. At one revolution per second, the vehicle would be traveling at a speed of four to five miles per hour.

The frequency of the sensor would give you an estimate of the number of teeth on the reluctor. This information will help you set the time base for your scope. The time base is set to allow all of the signals per revolution to appear on the display. If a wheel rotates at one revolution per second, the sensor and tone ring produces a 32-Hertz (Hz) frequency signal, the time base is calculated by dividing the frequency by 1.

This would be 0.03125 second, or 30 millisecond (mS) rounded down to the nearest mS. Set the time base for 30 to 40 mS. The amplitude of the signal for a inductive sensor will change as the speed of the reluctor increases. This will also affect the oscilloscope display.

A low amplitude signal can indicate an air gap or high resistance connector condition. If the oscilloscope you are using has a feature that will allow you to capture a series of frames, it will allow you examine the trace of one revolution of the reluctor. A cracked, damaged or missing reluctor can produce a signal that may not be processed by the BCM. The square wave signal does not need to be processed by the BCM; it is a direct input. Trouble Codes C1141 thru C1144 can be caused by a missing tooth and can be verified with a scope.

The aftermarket technician has to be more proficient in diagnosing system failures. He or she has to be familiar with more than one manufacturer and be able to understand their methods of diagnosis verses the dealership technician who deals with one manufacturer. The scan tool and service information are the primary tools, but a through knowledge of fundamental mechanical and electronic component operation is also an important tool in affecting the right fix the first time. 

The following two tabs change content below.
Latest articles from our other sites:

Check Out The October Issue Of Brake & Front End Magazine

The digital version of the October issue of Brake & Front End magazine is available online. CLICK HERE to access the easy-to-view digital version that features articles on Rotor Failure, Independent...More

Arnott Introduces New Right And Left Front Air Struts For 2000-'06 E53 Chassis BMW X5 With 4-Corner Air Leveling

Arnott Air Suspension Products has announced the introduction of new Arnott-engineered aftermarket air suspension struts for the front of the 2000-'06 BMW X5 (E53 Chassis) with 4-corner air leveling. Arnott's...More

Acura: Clunk Noise While Turning

Model: Acura RSX 2005-’06 Symptom: The front suspension makes a ­clunking noise while turning. Probable Cause: The front springs are moving on the spring seats. Corrective Action: Replace both...More

Inside Import Car Collision Warning, Automatic Braking Systems

Anything that moves under its own power also has to stop, so brakes have been a safety feature on cars since day one. Over the years, technical innovations such as antilock brakes (ABS) have ­improved...More

New Snap-on Heavy Duty Catalog Offers Array Of Performance-Enhancing Tools And Equipment

The new Snap-on Heavy Duty Catalog showcases some of the most innovative tools and equipment around, including an assortment of hand tools, power tools, shop and tech equipment, tool storage units, mobile...More

Analyzing the Cylinder Pressure Waveform from a Running Engine, Part 3

By Vasyl Postolovskyi and Olle Gladso Contributing Writers and Instructors at Riverland Technical and Community College in Albert Lea, MN   In Part 1 of this Maximizing Tools series, we discussed...More

Battery Service and Diagnosis

A good battery with an adequate charge is absolutely essential for reliable cold starting. A weak battery, or one that is rundown, may not deliver enough amps to crank the engine when temperatures...More

Chemical Gasketing: Cleaning the Surface

Service technicians can now use chemical gaskets where OEs had originally used formed-in-place or pre-cut gaskets during vehicle assembly. In addition to complying with OE specs, chemical gaskets are...More