Use the following equation to convert your recorded
RPM to Frequency Hz = RPM ÷ 30.
Typical Vacuum to Frequency Results (Ford)
Hg (Vacuum)
Hz (Hertz)
0
159
3
150
6
141
9
133
12
125
15
117
18
109
• A good sensor should show an increase or
decrease in the output voltage as the sensor is
opened and closed. A bad sensor will have no
change in resistance
• A good sensors output voltage or frequency (RPM)
fall within manufacturers specifications at 0 Hg. or
decrease with increasing vacuum.
• A bad sensors output voltage or frequency (RPM)
won’t fall within manufacturers specifications at 0
Hg. or show change with increased vacuum.
Oxygen Sensor O2
The Oxygen Sensor is used to measure the exhaust
gas concentration in the exhaust system. The ECU
uses the information to calculate and, if required,
adjust the air fuel ratio so that catalytic converters
can function efficiently. The sensor sends
information to the ECU based on the amount of
oxygen in the exhaust system and adjusts the air/
fuel ratio as needed. The two most common types
of O2 Sensors used are Zirconia and Titania. In
addition, when testing these two types you’ll need to
know if they are heated or unheated. If the sensor
has 3 or more wires, then your vehicle uses a
heated O2 sensor.
• A low voltage, high resistance, indicates a lean
exhaust, or too much oxygen.
• A high voltage, low resistance, indicates a rich
exhaust, or not enough oxygen.
Refer to illustration for appearance differences of
the two sensor types.
ENGINE SENSORS TESTS CONT.
Any time dealing with the exhaust system let the
vehicle cool down before proceeding. Although
these sensors can be checked in the vehicle, the
following test is done with the sensor removed.
NOTE: Never apply external voltage to the zirconia
sensors for testing, this may damage it.
1. Remove the Oxygen Sensor from the vehicle,
use the special slotted socket to avoid damaging
the wires.
2. Insert BLACK test lead into COM test lead jack.
3. Insert RED test lead into test lead jack.
O2 Heater Circuit
The following is for testing the heater circuit of the
O2 Sensor. Refer to your vehicles service manual for
the location of the heater pins in the wiring connector.
1. Add the alligator clips and connect the RED
clip to either of the two pins.
2. Connect the BLACK clip to remaining heater pin.
3. Turn the meters range selector to the 200Ω range.
4. View and record the display readings. Compare
them to the manufacturer’s specification in your
vehicles service manual. When completed remove
the test leads from the sensor.
O2 Sensor Circuit
The following is for testing the Oxygen Sensor
Circuit. Refer to your vehicles service manual for
the location of the ground pin and the signal pin in
the wiring connector. Also, know the type of O2
Sensor your vehicle uses, Zirconia type or Titania
type. A propane torch is needed to conduct this test.
1. Connect the BLACK alligator clip to the sensors
ground pin.
There are two different ways the sensor could be
grounded. The outside housing of the sensor, or the
ground will be in the wire harness connection. 1 and
3 wire sensors use the housing, while 2 and 4 wire
sensors have the ground in the harness connection.
2. Connect RED alligator clip to sensors SIGNAL pin.
3. Turn the meters range selector to 2V for
Zirconia or 200Ω for Titania.
4. Lock the pliers on the hex socket drive of the sensor.
5. Secure and light the propane torch and set it to a
mild flame. Heat the sensors tip as hot as possible
with the mild flame. Do not heat the tip to the point
of glowing.
The oxygen sensor must be hot, about 600 degrees
or higher, before it will start to generate a voltage
signal. Hold the sensor as close as possible to the
torch flame to quench the sensor tip. This will deplete
the sensor of oxygen signaling a Fuel Rich Condition.
ƱⅤ
Ʌ
°
Heated Type
3-4 Wires
8
Unheated Type
1-2 Wires
