BMW 3 (E46). Manual — part 240

Abbreviation

Component or system

Abbreviation

Component or system

GM

general module (see ZKE)

SRS

supplemental restraint
system-airbag

HPS

head protection system

TCM

transmission control module

IHKA

automatic heating and air
conditioning system

TDC

top dead center

IHKR

manual heating and air
conditioning system

TLEV

transitional low emissions
vehicle

ITS

head protection system

TXD

transmit data line

KL 15

battery positive, ignition
switch on "run"

UIS

ultrasonic interior protection

KL 30

battery positive "hot" all the
time

ULEV

ultra low emissions vehicle

KL 31

battery/chassis ground

ZKE

central body electronics

600-4

Electrical
Troubleshooting

Four things are required for current to
flow in any electrical circuit: a voltage
source, wires or connections to
transport the voltage, a load or device
that uses the electricity, and a
connection to ground.

Most problems can be found using a
digital multimeter (volt/ohm/amp meter)
to check the following:

Voltage supply

Breaks in the wiring (infinite
resistance/no continuity)

A path to ground that completes
the circuit.

Electric current is logical in its flow,
always moving from the voltage source
toward ground. Electrical faults can
usually be located through a process
of elimination. When troubleshooting a
complex circuit, separate the circuit into
smaller parts. General tests outlined
below may be helpful in finding
electrical problems. The information is
most helpful when used with wiring
diagrams.

Be sure to analyze the problem. Use
wiring diagrams to determine the most
likely cause. Get an understanding of
how the circuit works by following the
circuit from ground back to the power
source.

When making test connections at
connectors and components, use care
to avoid spreading or damaging the
connectors or terminals. Some tests
may require jumper wires to bypass

components or connections in the
wiring harness. When connecting
jumper wires, use blade connectors at
the wire ends that match the size of the
terminal being tested. The small
internal contacts are easily spread
apart, and this can cause intermittent
or faulty connections that can lead to
more problems.

Voltage and voltage drops

Wires, connectors, and switches that
carry current are designed with very
low resistance so that current flows
with a minimum loss of voltage. A
voltage drop is caused by higher than
normal resistance in a circuit. This
additional resistance actually
decreases or stops the flow of current.
A voltage drop can be noticed by
problems ranging from dim headlights
to sluggish wipers. Some common
sources of voltage drops are corroded
or dirty switches, dirty or corroded
connections or contacts, and loose or
corroded ground wires and ground
connections.

A voltage drop test is a good test to
make if current is flowing through the
circuit, but the circuit is not operating
correctly. A voltage drop test will help
to pinpoint a corroded ground strap or
a faulty switch. Normally, there should
be less than 1 volt drop across most
wires or closed switches. A voltage
drop across a connector or short cable
should not exceed 0.5 volts.

Note:

A voltage drop test is generally
more accurate than a simple
resistance check because the
resistances involved are often too
small to measure with most
ohmmeters. For example, a

resistance as small as 0.02 ohms
would results in a 3 volt drop in a
typical 150 amp starter circuit.
(150 amps x 0.02 ohms =3 volts).

Keep in mind that voltage with the
key on and voltage with the engine
running are not the same. With the
ignition on and the engine off
(battery voltage), voltage should
be approximately 12.6 volts. With
the engine running (charging
voltage), voltage should be
approximately 14.0 volts. Measure
voltage at the battery with the
ignition on and then with the
engine running to get exact
measurements.

Voltage, measuring

Connect digital multimeter negative
lead to a reliable ground point on car.

Note:

The negative (-) battery terminal is
always a good ground point.

-

Connect digital multimeter positive
lead to point in circuit you wish to
measure.

If a reading is obtained, current is
flowing through circuit.

Note:

The voltage reading should not deviate
more than 1 volt from voltage at the
battery. If voltage drop is more than
this, check for a corroded connector or
loose ground wire.