B120C

DTC B120C Theft alarm siren Flat Battery

CAUTION:
Before replacing the ECU or sensor, ensure that the power supply circuit, the ground circuit and the communication circuit are normal.

DIAGNOSTIC FUNCTION

The diagnostic trouble code No.B120C is set when the voltage of the rechargeable battery is low, or when the battery inside the security alarm siren has an error.
NOTE:
The rechargeable battery integrated in the security alarm siren is charged by turning the ignition switch to the ON position.

PROBABLE CAUSES

- Abnormality in theft alarm siren

- Service life of rechargeable battery

- Since the vehicle had been stationary for long time, the rechargeable battery remained uncharged.
This reduced voltage.

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)

Using scan tool MB991958, read the ETACS-ECU diagnostic trouble code.

Recheck whether the diagnosis trouble code is set.

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)Charge the rechargeable battery of the security alarm siren by turning the ignition switch to the ON position. (In principle, charge the battery for 30 minutes or more.)
(2)Erase the diagnosis trouble code.
(3)After the diagnosis trouble code is erased, turn the ignition switch to the LOCK
(OFF) position.
(4)Activate the security alarm once, and then cancel it.
NOTE:
Note that after erasing diagnostic trouble code No.B120C, if the ignition switch is turned from the LOCK (OFF) position to the ON position before activating the security alarm, diagnosis trouble code No.B120C will be set even though the system is normal.

(5)Turn the ignition switch from the LOCK (OFF) position to the ON position.
(6)On completion, check that the diagnosis trouble code is not reset.

Q. Is the DTC set?

YES Replace the theft alarm siren.

NO Diagnosis complete.