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DTC C1785: Fault Detection Signal Failure
 
 
caution
  • If there is any problem in the CAN bus lines, an incorrect diagnostic trouble code may be set. Prior to this diagnosis, diagnose the CAN bus lines.
  • Whenever the ECU is replaced, ensure that the communication circuit is normal.
  • When diagnostic trouble code No.C1785 is set in ACC-ECU, the diagnostic trouble code may also be set in ETACS-ECU. When the diagnostic trouble code is set in ETACS-ECU, perform the diagnosis of the diagnostic trouble code for ETACS-ECU first.
 
 
OPERATION
ACC-ECU receives the vehicle information stored in ETACS-ECU via CAN bus lines.
 
 
DIAGNOSTIC TROUBLE CODE SET CONDITION
This diagnostic trouble code is set when the abnormality below is detected:
  • The malfunction detection control signal, which is sent from the ETACS-ECU, cannot be received for a certain period.
 
 
PROBABLE CAUSES
  • Malfunction of the CAN bus line
  • Malfunction of ETACS-ECU
  • Malfunction of ACC-ECU

 
 
DIAGNOSIS
STEP 1. Diagnose the CAN bus line.
(1)
cautionTo prevent damage to scan tool (M.U.T.-III), always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool (M.U.T.-III).
Connect scan tool (M.U.T.-III). Refer to "How to connect the Scan Tool (M.U.T.-III) ."
(2) Turn the ignition switch to the "ON" position.
(3) Diagnose the CAN bus line. (Refer to GROUP 54C - Explanation About The Scan Tool (M.U.T.-III) Can Bus Diagnostics )
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Is the check result normal?
Go to Step 2
Repair the CAN bus lines (Refer to GROUP 54C - Diagnosis, Can Bus Diagnostics Table ).
 
STEP 2. Scan tool (M.U.T.-III) other system diagnostic trouble code.
Check the ETACS diagnostic trouble code (Refer to GROUP 54A - Diagnosis, Diagnostic Trouble Code Chart ).
Is the diagnostic trouble code set?
Perform the relevant troubleshooting.
Go to Step 3
 
STEP 3. Scan tool (M.U.T.-III) other system diagnostic trouble code.
Is diagnostic trouble code No.U1190 set?
Replace the ETACS-ECU (Refer to GROUP 54A - ETACS-ECU ).
Go to Step 4
 
STEP 4. Check whether the diagnostic trouble code is set again.
Is diagnostic trouble code No.C1785 set?
Replace the ACC-ECU (Refer to ).
Intermittent malfunction. (Refer to GROUP 00 - How to Cope with Intermittent Malfunction ).