ABS wheel speed sensor (digital) - voltage

The purpose of this test is to evaluate the operation of a digital Antilock Brake System (ABS) wheel speed sensor based on the output voltage and frequency.

Connection guidance

Connection for diagnostic work will vary dependent on application.

Technicians should whenever possible gain access to the test circuit without damage to seals and insulation. If this is not possible then make sure appropriate repairs are completed.

General connection advice

PicoScope offers a range of options within the test kits.

Dependent on difficulty of access, choose from:

  1. Breakout leads.
  2. Back-pinning probes.

Testing sensors and actuators (to include relevant circuit/connectors):

  • When testing a sensor, it is desirable to gain access at the control unit.
  • When testing an actuator, it is desirable to gain access at the actuator.

How to perform the test

Access to individual wheel-speed sensors may be difficult.

All wheel-speed sensors connect to the ABS control module, which is usually located in the engine bay.

  1. Use manufacturer data to identify the wheel speed sensor circuits.

  2. Connect PicoScope to the suspect sensor(s).

  3. Minimise the help page and with the example waveform on your screen PicoScope has already selected suitable scales for you to capture a waveform.

  4. Turn the ignition on but do not start the engine.

  5. Select Go or press the space bar to see live data.

  6. With the suspect wheel(s) raised, rotate it by hand. This will be sufficient to produce an output from a good speed sensor.

  7. With your live waveform on screen, select Stop or press the space bar to stop your capture.

  8. Use the Waveform Buffer and Zoom tools to examine your waveform.

NOTE:

PicoScope can be connected to gather waveforms from 2 or more driven wheels. In this case, the vehicle should be securely fixed onto a wheel free lift in order to drive the wheels to obtain waveforms.

Example waveform

Waveform notes

In this example, Channel A is connected to the front left wheel and Channel B to the front right.

These known good waveforms have the following characteristics:

A square wave structure with the voltages switching between two, fixed, levels, respectively at 0.45 V and 1.0 V (note: voltage levels will vary across different manufacturers).

The square wave frequency increases in proportion to the wheel speed.

Waveform Library

Go to the drop-down menu bar at the lower left corner of the Waveform Library window and select, ABS or wheel speed sensor (digital / hall effect).

Further guidance

Wheel speed sensors provide wheel and road speed feedback to ABS and their derivative active vehicle safety systems (i.e. stability and traction control systems etc.).

These systems are designed to provide corrective action (e.g. wheel braking or engine torque limitation) when the vehicle or wheel speed(s) have exceeded their normal operational tolerances, for example, during conditions of wheel slip, oversteer or understeer etc. Wheel speed sensors are critical to the operation of these systems and, therefore, the safe handling of a vehicle.

A digital ABS sensor includes a semiconductor (Hall effect sensor) that acts as either a conductor or an insulator depending on the orientation of any nearby magnetic field. When in the presence of an alternating magnetic field, as provided by a multipole rotor ring mounted in a wheel bearing seal or hub assembly, the sensor switches its output on and off. This action produces a digital square wave which is received by the ABS control module.

Digital wheel speed sensors require power to operate; hence they are referred to as active sensors. These sensors always have a positive supply voltage on one terminal; however, they may have one of two terminal configurations:

  • Three pin sensors have a dedicated earth reference circuit; whereas
  • Two pin sensors have a combined signal and earth reference circuit. In these sensors,  the reference voltage floats at the level of the signal.

An ABS control module expects similar (within a given tolerance) square wave frequencies from all the vehicle’s wheel speed sensors and uses any differences to calculate the timing and scale of its interventions.

If one, or more, wheel speed signals continuously falls outside of normal parameters, the control module may turn the ABS function off. A driver warning light will be illuminated but, as with any electrical fault on ABS, normal hydraulic braking is maintained.

Wheel speed sensors and their multipole rotor rings are exposed to the elements and have to operate under conditions of constant vibration and movement. As such, common faults are:

  • sensor signal failures, caused by chafed or fractured circuit wiring, sensor or connector corrosion, or incorrect sensor fitment; and
  • rotor ring related problems arising from damage during fitment, a build-up of ferrous material, or an excessive air gap between the sensor and the pulse wheel.

Diagnostic trouble codes

Selection of component related Diagnostic Trouble Codes (DTCs):

C0000 - Vehicle Speed Information Circuit Malfunction

C0035 - Left Front Wheel Speed Circuit Malfunction

C0036 - Left Front Wheel Speed Sensor Circuit Range/Performance

C0040 - Right Front Wheel Speed Circuit Malfunction

C0041 - Right Front Wheel Speed Sensor Circuit Range/Performance

C0045 - Left Rear Wheel Speed Circuit Malfunction

C0046 - Left Rear Wheel Speed Sensor Circuit Range/Performance

C0050 - Right Rear Wheel Speed Circuit Malfunction

C0051 - Right Rear Wheel Speed Sensor Circuit Range/Performance

C0221 - Right Front Wheel Speed Sensor Circuit Open

C0222 - Right Front Wheel Speed Signal Missing

C0223 - Right Front Wheel Speed Signal Erratic

C0225 - Left Front Wheel Speed Sensor Circuit Open

C0226 - Left Front Wheel Speed Signal Missing

C0227 - Left Front Wheel Speed Signal Erratic

C0229 - Drop Out of Front Wheel Speed Signals

C0235 - Rear Wheel Speed Signal Circuit Open

C0236 - Rear Wheel Speed Signal Circuit Missing

C0237 - Rear Wheel Speed Signal Erratic

C0238 - Wheel Speed Mismatch

C0245 - Wheel Speed Sensor Frequency Error

C0300 - Rear Speed Sensor Malfunction

C0305 - Front Speed Sensor Malfunction

GT072

Disclaimer
This help topic is subject to changes without notification. The information within is carefully checked and considered to be correct. This information is an example of our investigations and findings and is not a definitive procedure. Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test settings.

Suitable accessories

  • Premium 6-way breakout lead set

    £269.00

  • Back-pinning Probe Set

    £40.00

  • Flexible Back-pinning Probe

    £3.00

  • PicoScope Battery Clip

    £2.75

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Guided test: ABS wheel speed sensor (digital) - voltage