Code No. C1901:
Vehicle speed signal
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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  ).
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DIAGNOSTIC FUNCTION
ETACS-ECU receives the wheel speed information from ABS-ECU or ASTC-ECU via the CAN-bus
line. Although ETACS-ECU receives the information that the wheel is not currently rotated from ABS-ECU
or ASTC-ECU, if the TPMS transmitter sends the information that the wheel is rotated, this code
is set.
PROBABLE CAUSES
The most likely causes for this diagnosis code to be set is:
- Damaged wiring harness and connector
- Malfunction of TPMS transmitter
- Malfunction of ETACS-ECU
- Malfunction of ABS-ECU or ASTC-ECU
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STEP 1. M.U.T.-III CAN bus diagnosis.
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Use the M.U.T.-III to diagnose the CAN bus lines.
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Q.
Is the check result normal?
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 Go to Step 3.
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 Repair the CAN bus lines (Refer to GROUP 54C - CAN Bus Diagnostics Table ).
On completion, go to Step 2.
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STEP 2. Diagnosis code recheck after resetting CAN bus lines.
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Recheck if diagnosis code No. C1901 is set.
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(1)Turn the ignition switch from the "LOCK" (OFF) to "ON" position.
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(2)Check if the diagnosis code is set.
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(3)Turn the ignition switch to the "LOCK" (OFF) position.
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Q.
Is the diagnosis code set?
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Go to Step 3.
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The procedure is complete.
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STEP 3. Using M.U.T.-III other system diagnosis code.
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Check if the diagnosis code is set in the ABS-ECU or ASTC-ECU.
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Q.
Is the diagnosis code set?
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Carry out the troubleshooting for ABS-ECU (Refer to GROUP 35B - Troubleshooting)
or ASTC-ECU (Refer to GROUP 35C - Troubleshooting). Then go to Step 5.
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Go to Step 4.
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STEP 4. Check the TPMS transmitter acceleration.
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Check the acceleration value sent by each TPMS transmitter by performing the transmitter
check using the M.U.T.-III (Refer to ) when the vehicle is stationary.
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- Item 31: Acceleration, Tyre1
- Item 32: Acceleration, Tyre2
- Item 33: Acceleration, Tyre3
- Item 34: Acceleration, Tyre4
- Item 35: Acceleration, Tyre5
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OK:
Acceleration value: 5G or less
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Q.
Is the check result normal?
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Replace the ETACS-ECU (Refer to GROUP 54A - ETACS-ECU), and register
ID codes (Refer to ). Then go to Step 5.
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Replace the TPMS transmitter (Refer to ), and register
ID codes (Refer to ). Then go to Step 5.
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STEP 5. Check whether the diagnosis code is set again.
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Recheck if the diagnosis code is set.
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(1)Turn the ignition switch from the "LOCK" (OFF) to "ON" position.
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(2)Check if the diagnosis code is set.
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(3)Turn the ignition switch to the "LOCK" (OFF) position.
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Q.
Is diagnosis code No. C1901 set?
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Start over at Step 1.
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The procedure is complete.
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