DTC B120C: Theft alarm siren Flat Battery: Diagnosis

WARNING: This page is about a different car, the 2014 Mitsubishi Outlander. However, it is still accessible from the selected car via links, so may be relevant.

Using scan tool (M.U.T.-III), read the ETACS-ECU diagnostic trouble code.

Recheck whether the DTC is stored.

CAUTION: To prevent damage to scan tool (M.U.T.-III), always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool (M.U.T.-III).

Connect scan tool (M.U.T.-III). Refer to "HOW TO CONNECT SCAN TOOL (M.U.T.-III) ."

Charge the rechargeable battery of the theft-alarm siren by turning the ignition switch to the ON position. (In principle, charge the battery for 30 minutes or more.)
Erase the DTC.
After the DTC is erased, turn the ignition switch to the LOCK (OFF) position.
Activate the theft-alarm once, and then cancel it.
NOTE: Note that after erasing DTC No. B120C, if the ignition switch is turned from the LOCK (OFF) position to the ON position before activating the theft-alarm, DTC No. B120C will be stored even though the system is normal.
Turn the ignition switch from the LOCK (OFF) position to the ON position.
On completion, check that the DTC is not stored again.

Q: Is the DTC stored?

YES: Replace the theft-alarm siren.
NO: Diagnosis complete.