Code No. C1790: FCM control signal (ASC)
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If a diagnosis code is set, be sure to diagnose the CAN bus line.
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DIAGNOSTIC FUNCTION
If the laser radar receives an unnecessary FCM-LS control response from the ASC-ECU, diagnosis code No. C1790 is set.
CHECK CONDITION
When all the following conditions are satisfied
- After the ignition switch is turned ON, two or more seconds passed.
- After the engine has started
PROBABLE CAUSES
- Malfunction of the CAN bus line (noise contamination)
- Malfunction of the ASC-ECU
- Malfunction of the laser radar
DIAGNOSIS PROCEDURE
STEP 1. M.U.T.-III CAN bus diagnosis
Use the M.U.T.-III to diagnose the CAN bus lines.
Q.
Is the check result normal?
Go to Step 2.
Repair the CAN bus line (Refer to GROUP 54C - Troubleshooting 
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STEP 2. Check whether the diagnosis code is set again.
Check again if the diagnosis code is set in the laser radar.
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(1)Erase the set diagnosis code.
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(2)Turn the ignition switch to the "LOCK" (OFF) position.
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(4)Check if the diagnosis code is set.
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Q.
Is the diagnosis code set?
Replace the ASC-ECU (Refer to GROUP 35C - Hydraulic Unit ).
Go to Step 3.
STEP 3. Check whether the diagnosis code is set again.
Check again if the diagnosis code is set in the laser radar.
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(1)Erase the set diagnosis code.
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(2)Turn the ignition switch to the "LOCK" (OFF) position.
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(4)Check if the diagnosis code is set.
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Q.
Is the diagnosis code set?
Replace the laser radar (Refer to ).
The trouble can be an intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/inspection Service Points - How to Cope with Intermittent Malfunction ).