Code No. C1901: Vehicle speed signal
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- If diagnosis code No. C1901 is set, diagnose the CAN bus lines.
- When replacing the ECU, always check that the communication circuit is normal.
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ETACS-ECU <Vehicles without KOS> or KOS-ECU receives the wheel speed information from ABS-ECU <Vehicles without ASC> or ASC-ECU <Vehicles with ASC> via the CAN-bus line. Although ETACS-ECU <Vehicles without KOS> or KOS-ECU receives the information that the wheel is not currently rotated from ABS-ECU <Vehicles without ASC> or ASC-ECU <Vehicles with ASC>, if the TPMS transmitter sends the information that the wheel is rotated, this code is set.
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- Malfunction of CAN bus line
- Damaged wiring harness and connector
- Malfunction of TPMS transmitter
- Malfunction of ETACS-ECU <Vehicles without KOS> or KOS-ECU
- Malfunction of ABS-ECU <Vehicles without ASC> or ASC-ECU <Vehicles with ASC>
- Malfunction of ETACS-ECU
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STEP 1. M.U.T.-III CAN bus diagnostics
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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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 Go to Step 3.
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 Repair the CAN bus lines (Refer to GROUP 54C - Troubleshooting). On completion, go to Step 2.
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STEP 2. Check whether the diagnosis code is set again.
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(1)Turn the ignition switch (engine starting switch) from the "LOCK" (OFF) to "ON" position.
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(2)Check if the diagnosis code is set.
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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. M.U.T.-III other system diagnosis code
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Check if the diagnosis code is set in the ABS-ECU <Vehicles without ASC> or ASC-ECU <Vehicles with ASC>.
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Q.
Is the check result normal?
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Go to Step 4.
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NO <Vehicles without ASC> : Carry out the troubleshooting for ABS-ECU (Refer to GROUP 35B - Diagnosis code chart).
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NO <Vehicles with ASC> : Carry out the troubleshooting for ASC-ECU (Refer to GROUP 35C - Diagnosis code chart).
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STEP 4. M.U.T.-III other system diagnosis code
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Check if the diagnosis code is set in the ETACS-ECU (Refer to GROUP 54A - ETACS, Diagnosis code chart).
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Q.
Is the check result normal?
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Go to Step 5.
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Troubleshoot the set diagnosis code (Refer to GROUP 54A - ETACS, Diagnosis code chart). Then go to Step 6.
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STEP 5. Check the TPMS transmitter acceleration.
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Check the acceleration value of each TPMS transmitter by the air pressure of data list (Refer to  ).
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OK: Acceleration value: 5G or less
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Q.
Is the check result OK?
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Replace the KOS-ECU (Refer to GROUP 42B - KOS-ECU ) <Vehicles without KOS> or ETACS-ECU (Refer to GROUP 54A - ETACS-ECU ) and register the ID codes. Then go to Step 6.
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Replace the TPMS transmitter and register ID codes (Refer to ). Then go to Step 6.
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STEP 6. Check whether the diagnosis code is set again.
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(1)Turn the ignition switch (engine starting switch) from the "LOCK" (OFF) to "ON" position.
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(2)Check if the diagnosis code is set.
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Q.
Is the diagnosis code set?
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Start over at Step 1.
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The procedure is complete.
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