Zirconia Sensor: Meter display reading should be >0.6V
Titania Sensor: Meter display should show variable
resistance as flame temperature changes.
6. Now move the torch flame away fron the sensor
tip. This will allow oxygen to be drawn into the flame
and signal a Fuel Lean Condition.
Zirconia Sensor: Meter display reading should be <0.4V
Titania Sensor: Meter display should show an over
range with resistance set at the highest range.
7. Let the sensor cool then repeat the above test to
verify the results.
8. Turn the propane torch off, let the sensor cool
and remove the alligator test clips.
• A good heater circuit’s output resistance is within
manufacturer’s specifications.
• A good sensor circuit signal changes when moving
from a rich to a lean exhaust condition.
• A bad heater circuit output resistance is not within
manufacturer’s specifications.
• A bad sensors signal does not change when
moving from a rich to lean exhaust condition.
• A bad sensors signal moves between lean to rich
condition to slowly, >3 seconds.
Typically drivers don’t react until the MIL (Check
Engine) light come on
The following are symptoms of a failing Oxygen
Sensor prior to the MIL getting triggered.
• Increased tailpipe emissions
• Increased fuel consumption
• Hesitation on acceleration
• Stalling or a rough idle
MAF Sensors
This sensor send a signal to the ECU indicating the
air volume entering the engine. There are three
types of MAF sensors, the signal sent may be a DC
voltage, high frequency, or a low frequency.
This meter can only test DC voltage and low
frequency MAF sensors. High frequency MAF
sensors were common on some 1989 and newer
GM vehicles. Refer to your vehicle service manual
for the type MAF sensor your vehicle uses.
1. Insert BLACK test lead into COM test lead jack.
2. Insert RED test lead into test lead jack.
3. Add the alligator clips and connect the RED
clip to the sensors signal pin (typically the center).
4. Connect the BLACK clip to a good body GROUND.
5. Refer to your service manual for the MAF
location, identify the power, ground, and signal pin
ENGINE SENSORS TESTS CONT.
locations. Typically you’ll find the signal pin in the
center of the three pins.
For this test you’ll need to back probe or pierce the
signal wire in the MAF wire connection.
Refer to vehicle service manual for best way to
connect to MAF signal wire.
6. Turn Ignition KOEO (Key on engine off, do not
start engine).
7. Turn the meters range selector to 20V DC range
for DC signals, and 4CYL for Frequency signals.
Your DC volts should be approximately 1V or less.
With a Frequency MAF your display reading should
be between 314 to 347 RPM’s, for the GM low
frequency type sensor, (display RPM x 10).
Refer to your service manual for your specific
vehicles MAF sensor specifications.
Use the following equation to convert your recorded
RPM to Frequency Hz = RPM ÷ 30.
8. Turn the Ignition to the ON position and start the
vehicle. Be sure all wires, and leads are clear of
moving parts. At idle the voltage and RPM reading
should increase from your earlier results. As you rev
the engine both values should continue to increase.
Refer to vehicle service manual for charts relating
MAF sensor voltage or frequency (RPM) to
increasing air flow.
Use the following equation to convert your recorded
RPM to Frequency Hz = RPM ÷ 30.
• A good sensors output voltage or frequency (RPM)
fall within manufacturer’s specifications with KOEO,
or increase with increased air flow.
• A bad sensors output voltage or frequency (RPM)
won’t fall within manufacturer’s specifications, or
show change with increased air flow.
Temperature Sensor
A typical Temperature Sensor or thermistor are
thermally sensitive resistors whose prime function is
to exhibit a large, predictable and precise change in
electrical resistance when subjected to a
corresponding change in body temperature. The
hotter the sensor gets, the lower the resistance
becomes.
Typical Thermistor applications:
• Engine Coolant Temp. (ECT)
• Vane Air Temp, (VAT)
• Air Change Temp. (ACT)
• Throttle Body Temp (TBB)
• Manifold Air Temp. (MAT)
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