Mitsubishi Electric 55624R(S)-MF Service Manual page 168

Problem
The headlights flash during an
alarm test, but the theft-alarm
horn does not sound.
The system is not deactivated
when, during an alarm test in
which the alarm is intentionally
activated, the door or trunk is
unlocked by using the key.
NOTE
1. If there is abnormally excessive play in the
installation of the key cylinder switch of the
t r u n k a n d f o r d o o r s , o r i f t h e r e i s i m p r o p e r
installation, or if there is a malfunction of the
switch itself, the signals to disarm the system
and to deactivate the alarm won't be sent to the
ECU.
In this instance, after the system has been
armed, the alarm will be activated even if the
door is opened by using the key.
If, however, there is a short-circuit malfunction
of key cylinder switch of door, the electronic
THEFT-ALARM SYSTEM
Probable cause
Damaged or disconnected
wiring of horn relay drive
circuit
Damaged or disconnected
wiring of diode
Malfunction of the theft-
alarm horn relay
Damaged or disconnected
wiring of key cylinder switch
input circuit
Malfunction of the key cylin-
der switch
Malfunction of the ECU
Check method
Check by following in-
dividual part and the
circuit check No. 10. 11
procedures. (P.54-177)
If a malfunction is indi-
checking the input sig-
ing individual part and
the circuit check No. 7
procedures. (P.54-175)
control unit will judge that there is a malfunction
of the detection switch if the ignition switch is
s w i t c h e d O N , a n d t h e a l a r m w i l l n o t b e s e t
thereafter until the short-circuit malfunction is
reset.
2. If there is a malfunction of the key cylinder
switch system (damaged or disconnected wir-
ing, or short-circuit), thus making it necessary to
prevent an incorrect (accidental) alarm, the
system should not be armed by using the key to
lock when all the doors are closed.
Remedy
Repair the harness or
replace the diode or the
horn relay.
Repair the harness or
replace the key cylinder.
Replace the ECU.