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DTC C1784 FCM switch fixed ON
 
 
caution
  • Whenever the ECU is replaced, ensure that the CAN bus lines are normal.
 
 
OPERATION
The FCM/LDW/AHB-ECU receives the forward collision mitigation system (FCM) and ultrasonic misacceleration mitigation system ON/OFF switch signal from the ASC-ECU via CAN communication.
 
 
DIAGNOSTIC FUNCTION AND TROUBLE JUDGMENT
This DTC is set when the abnormality below is detected:
  • The forward collision mitigation system (FCM) and ultrasonic misacceleration mitigation system ON/OFF switch remains on for at least one minute.
 
 
TROUBLESHOOTING HINTS
  • Malfunction of the forward collision mitigation system (FCM) and ultrasonic misacceleration mitigation system ON/OFF switch (Stuck on)
  • Malfunction of the ASC-ECU
  • Malfunction of the FCM/LDW/AHB-ECU
  • Damaged harness wires and connectors
 
 
DIAGNOSIS
Required Special Tools:
  • MB991223: Harness Set
  • MB992006: Extra Fine Probe
STEP 1. Using scan tool (M.U.T.-IIISE), check data list.
Check the ASC-ECU data list (Refer to GROUP 35C - Troubleshooting ).
(1)
cautionTo prevent damage to scan tool (M.U.T.-IIISE), always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool (M.U.T.-IIISE).
Connect scan tool (M.U.T.-IIISE). Refer to "How to connect Scan Tool (M.U.T.-IIISE) ."
(2) Check the input signals from the forward collision mitigation system (FCM) and ultrasonic misacceleration mitigation system ON/OFF switch.
  • When the forward collision mitigation system (FCM) and ultrasonic misacceleration mitigation system ON/OFF switch is pressed.
 
Item No.Item nameNormal condition
66FCM ON/OFF switchON
Item No.Item nameNormal condition
66FCM ON/OFF switchON
  • When the forward collision mitigation system (FCM) and ultrasonic misacceleration mitigation system ON/OFF switch is not pressed.
 
Item No.Item nameNormal condition
66FCM ON/OFF switchOFF
Item No.Item nameNormal condition
66FCM ON/OFF switchOFF
OK: Normal condition is displayed.
Is the check result normal?
Go to Step 2.
Go to Step 4.
 
STEP 2. Using scan tool (M.U.T.-IIISE), check data list.
Check the FCM/LDW/AHB-ECU data list (Refer to ).
  • When the forward collision mitigation system (FCM) and ultrasonic misacceleration mitigation system ON/OFF switch is pressed.
 
Item No.Item nameNormal condition
25FCM ON/OFF switchON
Item No.Item nameNormal condition
25FCM ON/OFF switchON
  • When the forward collision mitigation system (FCM) and ultrasonic misacceleration mitigation system ON/OFF switch is not pressed.
 
Item No.Item nameNormal condition
25FCM ON/OFF switchOFF
Item No.Item nameNormal condition
25FCM ON/OFF switchOFF
OK: Normal condition is displayed.
Is the check result normal?
Go to Step 3.
Replace the FCM/LDW/AHB-ECU (Refer to ).
 
STEP 3. Using scan tool (M.U.T.-IIISE), read the DTC again.
Check again if the DTC is set in the FCM/LDW/AHB-ECU.
(1) Erase the DTC.
(2) Turn the ignition switch from "LOCK" (OFF) position to "ON" position.
(3) Check if DTC is set.
Is the DTC set?
Replace the FCM/LDW/AHB-ECU (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 ).
 
STEP 4. Check of short to ground circuit in FCSW line between ASC-ECU connector and forward collision mitigation system (FCM) and ultrasonic misacceleration mitigation system ON/OFF switch connector.
Is the check result normal?
Go to Step 5.
Repair the connector(s) or wiring harness.
 
STEP 5. Check the forward collision mitigation system (FCM) and ultrasonic misacceleration mitigation system ON/OFF switch.
Refer to .
Is the check result normal?
Go to Step 6.
Replace the forward collision mitigation system (FCM) and ultrasonic misacceleration mitigation system ON/OFF switch (Refer to ).
 
STEP 6. Using scan tool (M.U.T.-IIISE), check data list.
Check the ASC-ECU data list (Refer to GROUP 35C - Troubleshooting ).
  • When the forward collision mitigation system (FCM) and ultrasonic misacceleration mitigation system ON/OFF switch is pressed.
 
Item No.Item nameNormal condition
66FCM ON/OFF switchON
Item No.Item nameNormal condition
66FCM ON/OFF switchON
  • When the forward collision mitigation system (FCM) and ultrasonic misacceleration mitigation system ON/OFF switch is not pressed.
 
Item No.Item nameNormal condition
66FCM ON/OFF switchOFF
Item No.Item nameNormal condition
66FCM ON/OFF switchOFF
OK: Normal condition is displayed.
Is the check result normal?
The trouble can be an intermittent malfunction (Refer to GROUP 00 - How to use Troubleshooting/inspection Service Points - How to Cope with Intermittent Malfunction ).
Replace the ASC-ECU (Refer to GROUP 35C - ASC-ECU ).