BMW 3 (E46). Manual — part 237

Voltage and polarity

The vehicle electrical system is a 12-volt
direct current (DC) negative-ground
system. A voltage regulator controls
system voltage at approximately 12-volts.
All circuits are grounded by direct or
indirect connection to the negative (-)
terminal of the battery. A number of
ground connections throughout the car
connect the wiring harness to chassis
ground. These circuits are completed by
the battery cable or ground strap
between the body and the battery
negative (-) terminal.

Wiring, fuses and relays

Electrical components connect using
one of the following:

Heavy cables with lug-type
connectors (battery and starter)

Electrical harnesses with keyed,
push-on connectors that lock into
place

Busses with modular connectors

With the exception of the starter and the
charging system, most electrical power
is routed from the ignition switch or the
battery through the main relay panel in
back of the glove compartment or the

main fuse box (arrow) above the glove
compartment. Fuses are color coded to
indicate current capacities.

The relays and control modules are
mounted in various places throughout
the vehicle. See

610 Electrical

Component Locations

.

Central Body Electronics (ZKE
V)

E46 vehicles are equipped with an
integrated complex of electronic modules
connected mostly via K-bus. This
system, called ZKE V, is primarily
controlled by the General Module (GM
V).

These functions are controlled directly
by the GM V:

Windshield wiper/washer system,
with optional Rain Sensor Interface.
See

611 Wipers and Washers

.

Central locking, power trunk
release, keyless entry (FZV). See

515 Central Locking and Anti-theft

.

Power window control. See

512

Door Windows

.

Car Memory/Key Memory. See

515 Central Locking and Anti-theft

.

Interior lighting. See

612

Switches

.

Alarm system (DWA). See

515

Central Locking and Anti-theft

.

Electronic consumer sleep mode,
described later in this section

Other functions are not directly
controlled by the GM V but
interconnected:

Rain sensor (AIC). See

611

Wipers and Washers

.

Sunroof operation (SHD). See

540 Sunroof

.

Seat memory (SM) and electrical
operation. See

520 Seats

.

Outside rear-view mirror control and
heating. See

510 Exterior Trim,

Bumpers

.

Windshield washer jet heating. See

611 Wipers and Washers

.

Redundant data storage

The following vehicle information is
stored redundantly in the instrument
cluster and the light switch module:

Vehicle identification number (VIN)

Total mileage

Service interval data

This redundancy means that the
instrument cluster or light module may
be replaced without loss of stored data.

The data between the two units is
compared each time the ignition is
switched on (KL 15 on). If the data does
not match the tamper warning dot
(arrow) in the mileage display will be
illuminated. Under certain circumstances

a fault code (DTC) will be set.

Resetting and resynchronizing of codes
and data requires the use of BMW scan
tools DIS or MoDiC.

Car Memory/Key Memory

A number of features and functions can
be customized to the driver(s)
preference. The identity of the vehicle
user is provided by a signal from the
keyless entry system (FZV).

Car Memory and Key Memory are
actually two separate functions,
although they are marketed as a
combined feature. See

515 Central

Locking and Anti-theft

for further details.

Electrical consumer sleep mode

Central body electronics (ZKE V) is
designed to bring the vehicle electrical
consumers into "sleep mode" after 16
minutes of inactivity.

In order to test sleep mode:

Switch ignition off.

Close all doors, trunk and hood.

Lock vehicle using central locking.

Wait 16 minutes.

If one of a number of inputs into the
General Module (GM V) is activated
before the vehicle is in sleep mode, the
16 minute cycle starts again. Once the
vehicle is in sleep mode, the GM V will
"wake up" if it receives a change of
signal from one of the following sensors: