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DTC C1801 ACC/FCM Auto Stoplight monitor
 
 
cautionBefore replacing the ECU, ensure that the communication circuit is normal.
 
 
OPERATION
The ASC-ECU illuminates the stoplight while the ACC or the FCM is braking the vehicle automatically. The ASC-ECU monitors whether the stoplights illuminate or go out.
 
 
 
DTC SET CONDITIONS
The ASC-ECU sets the DTC when it detects a malfunction during monitoring.
 
 
 
TROUBLESHOOTING HINTS
  • Damaged wiring harness and connectors
  • Malfunction of ETACS-ECU
  • Malfunction of ASC-ECU
 
 
 
 
DIAGNOSIS
Required Special Tools:
  • MB991223: Harness Set
  • MB992006: Extra Fine Probe
STEP 1. Check the stoplight switch.
The stoplights should illuminate when the brake pedal is depressed.
Is the check result normal?
Go to Step 2.
Carry out troubleshooting for the stoplights. Refer to GROUP 54A - Rear Combination Light .
 
STEP 2. Scan tool (M.U.T.-IIISE) actuator test.
(1)
cautionTo prevent damage to scan tool (M.U.T.-IIISE), always turn off the power supply mode of the electric motor switch before connecting or disconnecting scan tool (M.U.T.-IIISE).
Connect scan tool (M.U.T.-IIISE). Refer to "How to connect the Scan Tool (M.U.T.-IIISE) ."
(2) When the actuator test is performed, the stoplights should illuminate.
  • Item No. 11: Stoplight: ON (Refer to ).
Is the check result normal?
Go to Step 4.
Go to Step 3.
 
STEP 3. Check of short to power supply, short to ground, and open circuit in STLD line between ASC-ECU connector and ETACS-ECU connector.
Is the check result normal?
Go to Step 4.
Repair the connector(s) or wiring harness.
 
STEP 4. Check of short to power supply, short to ground, and open circuit in STP line between ASC-ECU connector and stoplight connector.
Is the check result normal?
Go to Step 5.
Repair the connector(s) or wiring harness.
 
STEP 5. Check whether the DTC is set again.
(1) Erase the DTC.
(2) Turn off the power supply mode of the electric motor switch.
(3) Turn on the power supply mode of the electric motor switch.
Is DTC No.C1801 set?
Replace the hydraulic unit (integrated with ASC-ECU) (Refer to ).
This diagnosis is complete.