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１８
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Typical thermistor applications are:
·
Engine Coolant Temp. (ECT)
·
Air Charge Temp. (ACT)
·
Manifold Air Temp. (MAT)
·
Vane Air Temp. (VAT)
·
Throttle Body Temp. (TBT)
Voltage Presence
·
Disconnect the vehicle wiring harness at the sensor.
·
Select the Voltage range with the rotary switch.
Insert:
·
Black lead in COM terminal.
·
Red lead in V/
Ω
/RPM terminal.
·
Connect the test probes in parallel:
positive (+) to the circuit coming from the power source, negative (-) to the
negative circuit from the sensor.
·
Turn the ignition switch ON; do not start 10 the engine.
Measurement should be 5-9 volts (check the manufacture
’s specifications).
Voltage Change Connect jumper wires between the connector and the sensor.
·
Connect the test probes in parallel:
Positive (+) to the circuit coming from the power source, negative (-) to the
Negative circuit from the sensor.
·
Start the engine.
The voltage should change as the temperature changes. This is the signal that
is sent to the computer for processing. Refer to the manufacturer
’s
specifications. If the voltage change is not within specifications, look for
sources of resistance due to poor connectors, connections or breaks in the
wiring.
[3] Potentionneter (Variable Resistance, 3-wire) Tests
The potentiometer is a variable resistor. The signal it generates is used by the
vehicle computer to determine position and direction of movement of a device
within the component.
Resistance
·
Set the rotary switch to the Resistance (
Ω
) setting.
·
Disconnect the sensor.
·
Connect the test probes to the signal line and to the ground (refer to
manufacturer
’s schematic).
Watch the display; the Ohms reading should change as the signal arm on the
potentiometer is moved (signal sweep).
Typical potentiometer applications are:
·
Throttle position Sensor (TPS)
·
Exhaust Gas Recirculation valve position Sensor (EVP)
·
Vane Flow Meter(VAF)
Potentiometers (Variable Resistance, 3-wire) Tests
Reference Voltage Test
·
Disconnect the vehicle wiring harness at the sensor.
·
Select the Voltage range with the rotary switch.
Insert:
·
Black lead in COM terminal.
·
Red lead in V/
Ω
/RPM terminal.
·
Connect the test probes in parallel:
Positive (+) to the computer reference voltage circuit, negative (-) to the
negative system ground circuit from the sensor.
·
Turn the ignition switch ON : do not start the engine.
Watch the display. Reading should be 5-9 volts (check the manuacturer
’s
specifications).
Potentiometers (Variable Resistance, 3-wire) Tests
Voltage Change
·
Connect jumper wires between the connector and the sensor.
·
Connect the test probe in parallel:
positive (+) to the signal line, negative (-) to the ground circuit.
·
Turn the ignition key ON, do not start the engine.
·
Observe the display. The voltage drop should change as the position of the
signal arm on the potentiometer moves (signal sweep).
Refer to the manufacturer
’s specifications. If the voltage change is not within
specifications, look for sources
of resistance due to poor
connectors,
connections
or
breaks in the wiring.
[4] Oxygen Sensor (02) Test
The Oxygen sensor samples
the amount of Oxygen in the
exhaust stream. The voltage
produced by the 02 sensor is a
direct ratio to the oxygen level
