B120A
DTC B120A Theft-alarm siren error
CAUTION:
Before replacing the ECU or sensor, ensure that the power supply circuit, the ground circuit and the communication circuit are normal.
TROUBLE JUDGMENT
- The theft-alarm siren communicates with the ETACS-ECU by the LIN via the LIN cutoff control unit. The diagnostic trouble code No. B120A is set if the communication data between the ETACS-ECU and theft-alarm siren has an error when the relay inside the LIN cutoff control unit is ON (alarm is not activated.)
TROUBLESHOOTING HINTS
Malfunction of theft-alarm siren
DIAGNOSIS
Required Special Tools:
- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: Vehicle Communication Interface (V.C.I.)
- MB991827: M.U.T.-III USB Cable
- MB991910: M.U.T.-III Main Harness A (Vehicles with CAN communication system)
STEP 1. Using scan tool MB991958, read the ETACS-ECU diagnostic trouble code.
Check if DTC is set to the ETACS-ECU.
CAUTION:
To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.
Connect scan tool MB991958. Refer to "How to connect scan tool (M.U.T.-III) Reading and Clearing Diagnostic Trouble Codes."
(1)Turn the ignition switch to the "ON" position.
(2)Check whether the ETACS-ECU DTC is set.
(3)Turn the ignition switch to the "LOCK" (OFF) position.
Q. Is the DTC set?
YES Diagnose the ETACS-ECU (Refer to Electronic Time and Alarm Control System (ETACS)).
NO Go to Step 2.
STEP 2. Theft-alarm siren operation check
(1)Set the theft-alarm to the "Ready to be triggered" condition.
(2)Open the driver's door by using the ignition key.
(3)Check that the theft-alarm siren sounds.
Q. Is the check result normal?
YES The trouble can be an intermittent malfunction How to Cope With Intermittent Malfunctions).
NO Go to Step 3.
STEP 3. Replace the theft-alarm siren temporarily, and check whether the diagnostic trouble code is set.
Check again if the diagnostic trouble code is set to the ETACS-ECU.
(1)Erase the diagnosis trouble code.
(2)Turn the ignition switch from the LOCK (OFF) position to the ON position.
(3)Check if diagnostic trouble code is set.
Q. Is the DTC set?
YES Replace the ETACS-ECU.
NO Replace the theft-alarm siren.