BOSCH
DME
MM
AND
M33
.1
COMPONENT
TESTS
AND
REPAIRS
Consult
Table
a
for
engine
application
information
for
the
Bosch
DME
3
.1
and
3
.3.1
systems
.
The
DME
3
.1
and
DME
3
.3
.1
systems
are
similar
in
opera-
tion,
with
knock
control
and
VANOS
operation
being
the
key
differences
.
DME
3
.1
engines
arenot
equipped
with
VANOS
or
knock
detectors,
while
the
DM
E3
.3
.1
system
is
.
CA
UTION-
Use
onty
a
digital
multimeter
when
testing
wiring
.
Use
of
an
analog
VOM
may
damage
the
engine
control
module
.
Fig
.
25
.
Mass
air
flow
sensor
.
Hot
wire
sensor
usedon
carswith
DME
Electrical
tests
of
the
main
and
fuel
pump
relays
and
the
3
.1
(1992
6-cylinder
models)
.
DME
engine
control
module
(ECM)
are
covered
earlier
in
this
section
.
Fuel
pump
tests
are
covered
in
160
Fuel
Tank
and
CAUTION-
Fuel
Pump
.
Use
only
a
digital
multimeter
when
checking
the
mass
air
flow
sensor
.
An
analog
meter
can
dam-
Mass
Air
Flow
Sensor
age
theair
flow
sensor
.
There
are
two
types
of
mass
air
flow
sensors
used
onthe
1
.
Disconnect
air
flow
sensor
from
air
cleaner
only
.
Leave
cars
covered
by
this
section
.
Testing
procedures
vary
de-
it
connected
to
duct
leading
to
intake
manifold
and
pending
on
type
installed
.
The
airflow
sensor
is
not
adjustable
leave
wiring
harness
connected
.
and
must
only
be
tested
with
a
digital
multimeter
.
Mass
Air
FlowSensor
Variants
"
1992
M50
engine
DME
M3
.1
.
.
.
.
...
..
mass
air
flow
sensor-hot
wire
"
1993-1995
M50
and
S50US
DMEM33
.1)
.
...
...
.
mass
air
flow
sensor-hot
film
Mass
air
flow
sensor
(hot
wire),
testing
and
replacing
When
the
engine
is
running,
a
current
is
used
to
heat
a
thin
wire
in
the
center
of
the
sensor
.
See
Fig
.
25
.
The
current
in
the
wire
is
regulated
to
maintain
a
temperature
of
100°C
more
than
the
air
passing
over
it
.
The
current
used
to
heat
the
wire
is
electronically
conneced
into
a
voltage
measurement
corre-
sponding
to
the
mass
of
intake
a¡
r
.
To
keep
the
wire
clean,
it
is
heated
to
a
temperature
of
about
1,000°C
(1,830°F)
for
one
second
.
This
"burn-off"
cycle
takes
place
automatically,
four
seconds
after
the
engine
is
tumed
off
.
lf
thehot
wire
breaks
or
if
there
is
no
output
from
the
air
flow
sensor,
the
ECM
automatically
switches
to
a
"limp-home"
mode
and
tucos
on
the
Check
Engine
light
.
The
engine
can
usually
be
started
and
driven
.
The
air
flow
sensor
has
no
inter-
nal
moving
parts
and
cannot
be
serviced
.
FUEL
INJECTION
130-
1
7
2
.
Start
engine
and
run
it
to
normal
operating
temperature
.
3
.
Rev
engine
toat
least
2,500
rpm,then
shut
it
off
.
Look
through
meter
at
hot
wire
.
After
approximately
four
sec-
onds
wire
should
glow
brightly
for
about
one
second
.
NOTE
-
If
the
wire
glowsas
specified,
then
the
airflow
meter
and
ECM
are
probably
operating
correctly
.
lf
the
wire
does
not
glow,
continue
testing
.
4
.
lf
the
wire
does
not
glow,
remove
air
flow
sensor
and
look
through
it
to
see
if
wire
is
broken
.
lf
wire
is
broken,
meter
will
have
to
be
replaced
.
5
.
Reinstall
air
flow
sensor
and
harness
connector
.
Peel
back
rubber
bootfrom
harness
connector
.
Working
from
rear
of
connector,
connect
digital
voltmeter
across
terminals
1
and
4
.
See
Fig
.
26
.
6
.
Start
and
rev
engine
toat
least
2,500
rpm,thenshut
it
off
.
After
about
4
seconds,
voltage
should
riseto
about
4
volts
for
about
one
second
.
lf
voltage
is
present,
but
wire
does
not
glow,
air
flow
sensor
is
faulty
and
should
be
replaced
.
7
.
lf
voltage
is
not
present
in
step
6,
turn
ignition
key
on
and
check
for
voltage
and
ground
at
sensor
.
There
should
beground
at
pin
4
.
There
should
be
positive
(+)
battery
voltage
at
pin
2
.
BOSCH
DME
M3
.1
AND
M32
.1
COMPONENT
TESTS
AND
REPAIRS
