Code No. C1225
Wheel speed sensor malfunction (output signal malfunction)
caution
If there is any problem in
the CAN bus lines, an incorrect diagnosis code may be set. Prior to this diagnosis, diagnose
the CAN bus lines (Refer to GROUP 54C - CAN Bus Diagnostics Table ).
OPERATION
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.
DIAGNOSIS CODE SET CONDITIONS
ASC-ECU monitors the signals from each wheel speed sensor. If any fault below is found
in these sensor signals, ASC-ECU will set this diagnosis code. When the abnormal wheel is identified,
code No. C1201, C1206, C1211, or C1216 is set.
Missing sensor signal
Sensor signal, which will not be created under normal operation
Significant difference among the ABS sensor signals
When the ABS control is being activated for 1 minute or more.
PROBABLE CAUSES
Current trouble
Improper installation of the wheel speed sensor
Adhesion of foreign materials on the wheel speed detection encoder
Deformation of the wheel speed detection encoder
Excessive gap between the wheel speed sensor and the wheel speed detection encoder
Damaged wiring harness and connectors
Wheel speed sensor malfunction
ASC-ECU malfunction
Past trouble
The following conditions may occur.
Only one side of the right and left wheels is rotated or only the front wheels
or rear wheels are rotated.
Unstable vehicle attitude
External noise interference
DIAGNOSIS PROCEDURE
STEP 1. M.U.T.-III CAN bus diagnosis
Use M.U.T.-III to diagnose the CAN bus lines.
Q.
Is the check result normal?
Go to Step 3.
Repair the CAN bus lines (Refer to GROUP 54C - CAN Bus
Diagnostics Table ). On completion, go to Step 2.
STEP 2. Diagnosis code recheck after resetting CAN bus lines
Q.
Is the diagnosis code No.C1225 set?
Go to Step 3.
The procedure is complete.
STEP 3. Check for wheel speed sensor installation
Check how the all wheel speed sensor is installed correctly (Disconnection of wheel speed
sensor, loose mounting bolt, etc.).
Q.
Is the check result normal?
Go to Step 4.
Reinstall the wheel speed sensor correctly (Refer to ).
STEP 4. Check for wheel speed sensor as a single unit
Refer to .
Q.
Is the check result normal?
Go to Step 5.
Replace the wheel speed sensor (Refer to ).
STEP 5. Check for wheel bearing looseness
note
If the wheel bearing are loose, the gap between the wheel speed sensor and magnetic encoder
may become excessive. Check the wheel bearing, which diagnosis code indicates, for looseness.
Front: Refer to GROUP 26 -On-vehicle Service .
Rear: Refer to GROUP 27 -On-vehicle Service .
Q.
Is the check result normal?
Go to Step 6
NO <Front> : Replace the hub knuckle assembly (Refer to GROUP 26 - Front
Axle Hub Assembly ).
NO <Rear> : Replace the rear wheel hub assembly (Refer to GROUP 27 - Rear
Axle Hub Assembly ).
STEP 6. Check of wheel speed detection encoder
Check the encoder for adhesion of foreign materials or deformation.
Q.
Is the check result normal?
Go to Step 7.
NO <Front> : Remove the foreign materials and clean the encoder so as not
to disturb the magnetization pattern on it while taking care of the magnet, magnetic substance,
and magnetic attraction. When the encoder is deformed, replace the hub knuckle assembly (Refer
to GROUP 26 - Front Axle Hub Assembly ).
NO <Rear> : Remove the foreign materials and clean the encoder so as not
to disturb the magnetization pattern on it while taking care of the magnet, magnetic substance,
and magnetic attraction. When the encoder is deformed, replace the rear wheel hub assembly (Refer
to GROUP 27 - Rear Axle Hub Assembly ).
STEP 7. Voltage measurement at the A-10 ABS-ECU connector
(1)Disconnect the ASC-ECU connector, connect special tool ABS check harness (MB992335)
to the harness-side connector, and then measure the voltage at the special tool connector side.
note
Do not connect the special tool ABS check harness (MB992335) to ASC-ECU.
(2)Turn the electric motor switch to the "ON" position. (3)Measure the voltage between the front wheel speed sensor power supply terminal
and the body earth, and between the front wheel speed sensor signal terminal and the body earth.
Wheel speed sensor
Check terminal
Power supply terminal
Signal terminal
FR
No. 18
No. 6
FL
No. 34
No. 22
RR
No. 19
No. 31
RL
No. 33
No. 20
OK: 1 volt or less
Q.
Is the check result normal?
Go to Step 8.
NO (Not normal at the terminal No. 18 or 6) : Go to Step 9.
NO (Not normal at the terminal No. 34 or 22) : Go to Step 10.
NO (Not normal at the terminal No. 19 or 31) : Go to Step 11.
NO (Not normal at the terminal No. 33 or 20) : Go to Step 12.
STEP 8. Resistance measurement at A-14 ASC-ECU connector
(1)Disconnect the ASC-ECU connector, connect special tool ABS check harness (MB992335)
to the harness-side connector, and then measure the resistance at the special tool connector
side.
note
Do not connect the special tool ABS check harness (MB992335) to ASC-ECU.
(2)Measure the resistance between the front wheel speed sensor power supply terminal
and the body earth, and between the front wheel speed sensor signal terminal and the body earth.
Wheel speed sensor
Check terminal
Power supply terminal
Signal terminal
FR
No. 18
No. 6
FL
No. 34
No. 22
RR
No. 19
No. 31
RL
No. 33
No. 20
OK: No continuity
Q.
Is the check result normal?
Go to Step 13.
NO (Not normal at the terminal No. 18 or 6) : Go to Step 9.
NO (Not normal at the terminal No. 34 or 22) : Go to Step 10.
NO (Not normal at the terminal No. 19 or 31) : Go to Step 11.
NO (Not normal at the terminal No. 33 or 20) : Go to Step 12.
The short circuit may be present in the front wheel speed sensor <RH> circuit.
Repair the wiring harness between A-14 ASC-ECU connector terminal No.6 and A-21 front wheel
speed sensor <RH> connector terminal No.1, and between A-14 ASC-ECU connector
terminal No.18 and A-21 front wheel speed sensor <RH> connector terminal No.2.
The short circuit may be present in the front wheel speed sensor <LH> circuit.
Repair the wiring harness between A-14 ASC-ECU connector terminal No.22 and A-18 front wheel
speed sensor <LH> connector terminal No.1, and between A-14 ASC-ECU connector
terminal No.34 and A-18 front wheel speed sensor <LH> connector terminal No.2.
The short circuit may be present in the rear wheel speed sensor <RH> circuit.
Repair the wiring harness between A-14 ASC-ECU connector terminal No.19 and C-27 rear wheel
speed sensor <RH> connector terminal No.2, and between A-14 ASC-ECU connector
terminal No.31 and C-27 rear wheel speed sensor <RH> connector terminal No.1.
The short circuit may be present in the rear wheel speed sensor <LH> circuit.
Repair the wiring harness between A-14 ASC-ECU connector terminal No.20 and C-15 rear wheel
speed sensor <LH> connector terminal No.1, and between A-14 ASC-ECU connector
terminal No.33 and C-15 rear wheel speed sensor <LH> connector terminal No.2.
Repair the defective connector.
STEP 13. Voltage measurement at the A-14 ASC-ECU connector
(1)Disconnect the ASC-ECU connector, connect special tool ABS check harness (MB992335)
to the ASC-ECU-side connector and harness-side connector, and then measure the voltage at the
special tool connector side. (2)Turn the electric motor switch to the "ON" position. (3)Measure the voltage between the front wheel speed sensor circuit power supply terminal
and the body earth and between the front wheel speed sensor circuit signal terminal and the
body earth.
Wheel speed sensor
Check terminal
Power supply terminal
Signal terminal
FR
No. 18
No. 6
FL
No. 34
No. 22
RR
No. 19
No. 31
RL
No. 33
No. 20
OK:
Approximately system voltage <Power supply terminal> 1V or less <Signal terminal>
Q.
Is the check result normal?
Go to Step 22.
NO (Not normal at the terminal No. 18 or 6) : Go to Step 14.
NO (Not normal at the terminal No. 34 or 22) : Go to Step 16.
NO (Not normal at the terminal No. 19 or 31) : Go to Step 18.
NO (Not normal at the terminal No. 33 or 20) : Go to Step 20.
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Go to Step 3.
Repair the CAN bus lines (Refer to GROUP 54C - CAN Bus
Diagnostics Table 
). On completion, go to Step 2.)
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: Go to Step 9.)
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