[Previous][Next]
DTC C1801 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.
 
 
 
PROBABLE CAUSES
  • Damaged wiring harness and connectors
  • ETACS-ECU malfunction
  • ASC-ECU malfunction
 
 
 
 
DIAGNOSIS
Required Special Tools:
  • MB991223: Harness Set
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. Using scan tool (M.U.T.-IIISE), check actuator test.
When the actuator test is performed, the stoplights should illuminate (Refer to ).
  • Item No.11: Stoplight: ON
Is the check result normal?
Go to Step 6.
Go to Step 3.
 
STEP 3. Voltage measurement at the ASC-ECU connector (ASTP terminal)
(1) Disconnect the ASC-ECU connector, and measure at the wiring harness side.
(2) Turn the ignition switch to the "ON" position.
(3) Measure the voltage between the ASC-ECU connector (ASTP terminal) and the body ground.
OK: The voltage should measure approximately 12 volts (battery positive voltage)
Is the check result normal?
Go to Step 5
Go to Step 4.
 
STEP 4. Resistance measurement at the ASC-ECU connector (ASTP terminal) and ETACS-ECU connector (STLD terminal)
(1) Disconnect the ASC-ECU connector and ETACS-ECU connector, and measure at the wiring harness side.
(2) Measure the resistance between the ASC-ECU connector (ASTP terminal) and the ETACS-ECU connector (STLD terminal).
OK: The resistance should be 2 ohms or less
Is the check result normal?
Replace the ETACS-ECU (Refer to GROUP 54A - ETACS ).
Repair the connector(s) or wiring harness.
 
STEP 5. Voltage measurement at the ETACS-ECU connector (STLD terminal)
(1) Do not disconnect the ETACS-ECU connector.
(2) Perform the actuator test (Refer to ).
  • Item No.11: Stoplight: ON
(3) Measure the voltage between terminal STLD and body ground by backprobing.
OK: 1 volt or less
Is the check result normal?
Replace the ETACS-ECU (Refer to GROUP 54A - ETACS ).
Replace the hydraulic unit (integrated with ASC-ECU) (Refer to ).
 
STEP 6. Check of open circuit in STP line between ETACS-ECU connector and ASC-ECU connector
Is the check result normal?
Go to Step 7
Repair the connector(s) or wiring harness.
 
STEP 7. Check whether the DTC is set again.
(1) Erase the DTC.
(2) Turn the ignition switch to the "LOCK" (OFF) position.
(3) Turn the ignition switch to the "ON" position.
(4) Perform the actuator test (Refer to ).
  • Item No.11: Stoplight: ON
Is DTC C1801 set?
Replace the hydraulic unit (integrated with ASC-ECU) (Refer to ).
Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/How to Cope with Intermittent Malfunctions ).