Thermistor Coolant sensor Air intake temperature sensor Ambient
temperature sensor Etc.
2_ Equipment :
Ohmmeter
3_Method(s) :
Connect across the two terminals.
4_ Results :
Most thermistors have a negative temperature coeff cient
(NTC). This means the resistance falls as temperature rises. A resistance check should give readings broadly as follows:
0 °C = 4500 Ω
20 °C = 1200 Ω
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1_Sensor:
Inductive Crankshaft speed and position ABS wheel speed Camshaft position.
2_Equipment:
Ohmmeter ,AC voltmeter
3_Method(s) :
A resistance test with the sensor disconnected AC voltage output with the engine cranking.
4_Results :
Values vary from approx. 200–400 Ω on some vehicles to 800–1200 Ω on others. The ‘sine wave’ output should
be approx. 5 V (less depending on engine speed.
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1_ Sensor:
Hall effect Ignition distributor Engine speed transmission speed Wheel speed Current fow in a wire
(ammeter amp clamp)
2_ Equipment :
DC voltmeter Logic probe Do NOT use an ohmmeter as this will damage the Hall chip.
3_Method(s) :
The voltage output measured as the engine or component is rotated slowly. The sensor is normally
supplied with a 5 Vor a 10–12 V.
4_Results :
This distributor switches between 0 and approx. 8 V as the Hall chip is magnetised or
not. Others switch between 0 and approx. 4 V A logic probe will read high and low as the sensor output switches.
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1_Sensor :
Optical Ignition distributor Rotational speed.
2_Equipment :
DC voltmeter
3_Method(s):
the device will normally be supplied with a stabilised voltage. Check the output wire signal as the device is rotated slowly.
4_Results :
Clear switching between low and high voltage.
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1_Sensor :
Variable resistance Throttle potentiometer Flap-type airf ow sensor Position sensor .
2_ Equipment :
DC voltmeter or Ohmmeter
3_Method(s):
This sensor is a variable resistor. If the supply is left connected then check the output on a DC voltmeter With the supply
disconnected, check the resistance.
4_Results :
The voltage should change smoothly from approx. 0 V to the supply voltage (often 5 V) Resistance should change smoothly.
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1_Sensor:
Strain gauges MAP sensor Torque stress
2_Equipment :
DC voltmeter
3_Method(s):
the normal supply to an externally mounted manifold absolute pressure (MAP) sensor is 5 V. Check the output as manifold pressure
changes either by snapping the throttle open, road testing or by using a vacuum pump on the sensor pipe.
4_Results:
he output should change between approx. 0 and 5 V as the manifold pressure changes. As a general guide 2.5 V at idle speed.
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1_ Sensor:
Variable capacitance
2_Equipment :
DC voltmeter
3_Method(s) :
Measure the voltage at the sensor
4_Results :
Small changes as the input to the sensor is varied – this is not diffcult to assess because of very low capacitance values.
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1_Sensor :
Accelerometer Knock sensors
2_ Equipment :
Scope
3_Method(s)
tap the engine block lightly (13 mm spanner) near the sensor .
4_Results
Oscillating output that drops back to zero If the whole system is operating, the engine will slow down if at idle speed .
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1_Sensor :
Hot wire Air fow
2_ Equipment :
DC voltmeter or duty cycle meter
3_Method(s):
This sensor includes electronic circuits to
condition the signal from the hot wire. The normal supply is either 5 or 12 V.
Measure the output voltage as engine speed/load is varied
4_Results:
The output should change between approx. 0 and 5 V as the air fow changes 0.4–1 V at idle is typical.
Or depending on the system in use the output may be digital.
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1_Sensor:
Oxygen Lambda sensor, EGO sensor ,HEGO sensor
2_Equipment :
DC voltmeter
3_Method(s):
the lambda sensor produces its own voltage a bit like a battery. This can be measured with the sensor connected to the system.
4_Results:
A voltage of approx. 450 mV (0.45 V) is the normal f gure produced at lambda value of one The voltage output, however,
should vary smoothly between 0.2 and 0.8 V as the mixture is controlled by the ECU.
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1_Sensor
Acceleration switch Dynamic position
Equipment
DC voltmeter
2_Method(s)
Measure the supply and output as the sensor is subjected to the required acceleration.
3_Results
A clear switching between say 0 and 12 .
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1_ Sensor
Rain and other unknown types.
Equipment
DC voltmeter
2_Method(s)
Locate output wire – by trial and error if necessary and measure dry/wet output (splash water on the screen with the sensor correctly
in position)
3_Results
A clear switching between distinct voltage levels .
