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34
Mass Air Flow (MAF) Sensors
This sensor sends a signal to the computer
indicating the amount of air entering the
engine. Depending on the sensor design, the
signal may be a dc voltage, low frequency, or
high frequency type. The CP7676 can only
test the dc voltage and low frequency type
of MAF sensors. The high frequency type
output a frequency that is too high for the
CP7676 to measure. The high frequency type
MAF is a 3-pin sensor used on 1989 and
newer GM vehicles. Refer to vehicle service
manual for the type of MAF sensor your
vehicle uses.
Test Procedure (see Fig. 31):
1. Insert BLACK test lead into the COM
test lead jack.
2. For DC Volts type MAF sensor, insert
RED test lead into the
V
test lead
jack.
For Low Frequency type MAF sensor,
insert RED test lead into the test
lead jack.
Fig. 31
3. Connect BLACK test lead to good
vehicle ground.
4. Connect RED test lead to MAF signal
wire.
Refer to vehicle service manual for
location of MAF signal wire.
You may have to backprobe or pierce
MAF signal wire in order to make
connection.
Refer to vehicle service manual for best
way to connect to MAF signal wire.
5. Turn Ignition Key ON, but do not start
engine!
6. Turn multimeter rotary switch to...
20V range for DC type MAF sensors.
4 Cylinder RPM X 10 position for Low
Frequency type MAF sensors.
7. View reading on display.
DC Volts Type Sensor:
Display reading should be approximately
1V or less depending on MAF sensor
manufacturer.
Low Frequency Type Sensor:
Display reading should be approximately
330RPM ± 5% for GM Low Frequency
MAF sensors.
For other Low Frequency type MAF
sensors refer to vehicle service manual
for MAF sensor specifications.
It is O.K. if last two display digits change
slightly while Key is ON.
Remember to multiply display reading by
10 to get actual RPM.
To convert RPM to Frequency or vice
versa, use equation below.
Frequency =
RPM
30
{Equation Only Valid for Multimeter in 4
Cylinder RPM X 10 Position}
Red
Black
Ground
DC
Only
Frequency
Only
Typical GM 1988 & older
Low Frequency type
MAF Sensor
Red