How to Test Wheel Speed Sensors

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Section 7

How to Test Wheel Speed Sensors

NOTE: At initial installation, no gap must exist between the sensor and the tooth wheel.

NOTE: After you install a hub, always check that the sensor is adjusted properly.

Operating the trailer can cause a gap to develop between the sensor and the tooth wheel. If the gap exceeds 0.040-inch, the system may not function correctly.

To adjust the sensor, twist and push the sensor through the sensor bracket as far as possible or until the sensor touches the tooth wheel.

Sensor Test Procedure

1. Disconnect power to the ECU/Valve Assembly.

2. Disconnect the sensor electrical connector from the ECU/Valve Assembly.

3. Connect the Volt/Ohm meter leads to the two wire component terminals inside the disconnected connector.

4. When checking the resistance, the meter must read 50-2000 ohms.

5. Check and replace the sensor and cables as required.

6. Repeat Steps 1-5 for each sensor in the system.

Sensor Output Voltage Test

1. Disconnect power from the ECU/Valve Assembly.

2. Connect the AC Volt/Ohm meter leads to the sensor terminals inside the connector.

3. Rotate the corresponding wheel at a constant speed of one-half revolution per second.

4. The output voltage must be greater than 0.2 volts AC.

5. When there is no reading:

a. Trace the cable to verify that the cable connects to the wheel you turned.

b. Check that you turned the correct wheel.

c. Check that the system is wired correctly.

d. Check that the sensor touches the tooth wheel.

6. If the Volt/Ohm meter still indicates no reading or a low reading after following the above procedures, check and replace the component and cables as required.

7. Repeat Steps 1-5 for each sensor in the system.

Check ABS Functions

· Meritor WABCO recommends that you test a vehicle's ABS after a new installation and after you diagnose, repair and erase faults in the ABS.

· Perform end of line check using TOOLBOX Software or the Pro-Link 9000.

ABS External Modulator Valve

Measure resistance across each valve solenoid coil terminal and ground on the ABS valve to ensure 4.0 to 8.0 ohms. Valve and cable pinouts are illustrated in Figure 7.1.

Figure 7.1

To check the cable and the ABS valve as one unit, measure resistance across pins 5 and 6 and 5 and 7 on the ECU connector of the harness. Resistance should be between 4.0 and 8.0 ohms for each measurement.

Figure 7.2

If resistance is greater than 8.0 ohms, clean the electrical contacts. Check the resistance again.

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