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E90 General Vehicle Electrical
Tilt Alarm Sensor
The tilt alarm sensor registers the vehicle rest position when it is armed and detects
changes in the position, e.g. jacking up the vehicle. The tilt alarm sensor is integrated in
the emergency current siren. The initialization procedure for the tilt alarm sensor is start-
ed 3 s after closing the last door and trunk lid. The tilt alarm sensor is operational 30 s
after initialization and is adopted in the alarm table.
If no feedback telegram is received from the emergency current siren or tilt alarm sensor,
this status is entered in the information memory of the anti-theft alarm system. The tilt
alarm sensor is not adopted in the alarm table.
If the tilt alarm sensor detects vehicle movement, a corresponding signal is sent to the
USIS. The anti-theft alarm system decides whether the movement is sufficient to trigger
an alarm.
To ensure a false alarm is not triggered as the result of the vehicle rocking, the angle val-
ues for the longitudinal and transverse axis are determined every 90 ms. An alarm is trig-
gered only if the vehicle remains in an inclined position for longer than approx. 1.5 s.
The alarm triggered by the tilt alarm sensor is stored in the ultrasonic passenger compart-
ment protection system.
Self-Monitoring of Emergency Current Siren
A self-monitoring facility that is activated immediately after the anti-theft alarm system
has been armed is implemented in the emergency current siren. The emergency current
siren monitors its own power supply and detects overvoltage, undervoltage and line break
(open-circuit).
If the emergency current siren detects a tampering attempt, it sends a corresponding sig-
nal to the USIS, irrespective of whether the DWA bus is affected and triggers a stand-
alone alarm.
Line Monitoring - DWA Bus
The ultrasonic passenger compartment protection system and the emergency current
siren are connected via the DWA bus. Immediately after arming the anti-theft alarm sys-
tem, the DWA bus is monitored cyclically every 2 s.
The anti-theft alarm system sends a line monitoring request on the DWA bus to the
emergency current siren.
The emergency current siren must respond within 100 ms. If no reply is received, the
request for line monitoring is sent a further two times. If still no response is received, the
Anti-theft alarm system triggers an alarm. The line monitoring facility is also active while
the alarm is triggered.
The anti-theft alarm system measures the system voltage. To avoid false alarms, the line
monitoring facility is switched off at a system voltage below 9 V. This avoids false alarms.
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