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- The wheel speed sensor is a kind of a pulse generator.
It consists of encoders (a plate on which north and south pole sides of the magnets are arranged
alternately) for detecting the wheel speed which rotates at the same speed of the wheels and
wheel speed sensors. This sensor outputs frequency pulse signals in proportion to the wheel
speed.
- The pulse signals, which the wheel speed sensor creates, are sent to ASC-ECU. ASC-ECU
uses the frequency of the pulse signals to determine the wheel speed.
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ASC-ECU monitors the voltage fluctuation in each wheel speed sensor circuit. If ASC-ECU
detects the open or short circuit in the circuit, it will set a diagnosis code.
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Current trouble
- Damaged wiring harness and connectors
- Noise interference
- Malfunction of wheel speed sensor
- ASC-ECU malfunction
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Past trouble
- Carry out diagnosis with particular emphasis on wiring harness and
connector failures between ASC-ECU and the wheel speed sensor. For diagnosis procedures, refer
to How to treat past trouble (GROUP 00 - How to Cope with Intermittent Malfunction ).
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Use M.U.T.-III to diagnose the CAN bus lines.
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Q.
Is the check result normal?
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Repair the CAN bus lines (Refer to GROUP 54C - Troubleshooting ).
On completion, go to Step 2.
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Q.
Is the diagnosis code No. C102B set?
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This diagnosis is complete.
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Check the following service data.
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- Item No.04: RR wheel speed sensor
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Q.
Is the check result normal?
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Intermittent malfunction (Refer to GROUP 00 - How to Cope with Intermittent
Malfunction ).
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(1)Disconnect the ASC-ECU connector, connect special tool ASC check harness (MB991997) to
the harness-side connector, and then measure the voltage at the special tool connector side.
note |
Do not connect the special tool to ASC-ECU.
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(2)Turn the ignition switch to the ON position. (3)Measure the voltage between the wheel speed sensor power supply terminal (signal
terminal) No. 43/the earth terminal No. 42 and the body earth. OK: 0 V
Q.
Is the check result normal?
Go to Step 5.
NO (Not normal at the terminal No. 43 or 42.) : Go to Step 7.
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Q.
Is the check result normal?
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Repair the defective connector.
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- Check for short circuit in wheel speed sensor <RR> circuit
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Q.
Is the check result normal?
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Replace the wheel speed sensor <RR>.
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Repair the wiring harness.
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(1)Disconnect the ASC-ECU connector, connect special tool ASC check harness (MB991997) to
the harness-side connector, and then measure the resistance at the special tool connector side.
note |
Do not connect the special tool to ASC-ECU.
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(2)Resistance between the wheel speed sensor power supply terminal (signal terminal)
No. 43/the earth terminal No. 42 and the body earth OK: Continuity exists (2 Ω or less)
Q.
Is the check result normal?
Go to Step 10.
NO (Not normal at the terminal No. 43 or 42.) : Go to Step 8.
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Q.
Is the check result normal?
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Repair the defective connector.
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- Check for short circuit in wheel speed sensor <RR> circuit
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Q.
Is the check result normal?
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Replace the wheel speed sensor <RR>.
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Repair the wiring harness.
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(1)Disconnect the ASC-ECU connector, connect special tool ASC check harness (MB991997) to
the ASC-ECU-side connector and harness-side connector, and then measure the voltage at the special
tool connector side. (2)Turn the ignition switch to the ON position. (3)Measure the voltage between the wheel speed sensor circuit power supply terminal
(signal terminal) No. 43 and the body earth. OK: Approximately battery voltage
Q.
Is the check result normal?
Go to Step 11.
Replace the ASC-ECU.
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Q.
Is the check result normal?
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Repair the defective connector.
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- Check for open circuit in wheel speed sensor <RR> circuit
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Q.
Is the check result normal?
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Repair the wiring harness.
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Q.
Is the check result normal?
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Replace the wheel speed sensor.
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(1)Erase the diagnosis code.
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(2)Drive the vehicle at 20 km/h or more.
note |
The ABS warning lamp does not turn OFF in some cases unless the vehicle runs at 20 km/h
or higher.
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Q.
Is the diagnosis code No. C102B set?
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Intermittent malfunction (Refer to GROUP 00 - How to Cope with Intermittent
Malfunction ).
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