4.4.2 Hall & Optic sensors
1. These sensors already provide the TCU with a square wave.
2. Hall sensors work with magnetic fields but it does not mean it is a magnetic sensor. Failure
to identify this will cause incorrect wiring and no operation.
3. They have three wires. Each sensor has a positive (12V), earth and signal out pin.
Connecting these wrong may damage the TCU or the sensor permanently. If you are not
sure which pin is which, ask your agent to bench test it first with protection resistors to get
correct pin-outs.
4. The TCU has an extra pull-up resistor of 2.2KOhm set with the jumper. If erratic misfires
occur, another 1K Ohm resister may be connected between the signal and 12V wire on the
sensor.
5. If the sensor requires a resistor in the positive wire to limit current, it must be put in
separately.
Testing a Hall or Optic sensor
•
• These sensors normally have 3 wires. A supply wire, normally 12V, an earth wire and a signal
out. This sensor has electronic components that require power to operate. Connecting this
sensor wrong my damage it permanently. First test for resistance on all the pins and swap the
test leads around to make sure it is not a magnetic sensor. Put the meter on diode test and
measure voltage drops over all the pins. You should get V drops between 0.5V to 1.9V. This is
your indicator that you have an electronic unit.
Bat+
1 K
1 K
Sensor
+
-
Multi M eter
• Now take 2 x 1K resistors and tie one end of each to the +12V. This will ensure that if you
connect the supply wrong you will not damage the component as the resistor will limit the
current to 10mA. Now put the ground on one pin and the 2 resisters on the other pins. Put the
meter black wire on earth for the remainder of the tests. Connect the meter red wire to any of
the other pins. Now move an iron object to the sensor or in the gap and away. If the signal
varies between 0V and 12V then this pin may be the signal output of the sensor. Now put the
red wire on the other pin and repeat the iron process. This voltage should not change. It may
be less than 12V due to the drop over the resistor. If so then this is the supply pin. With other
words one of the resistor pins should respond rapidly to iron pulses while the other one
remains fairly constant.
• Now change the earth pin to the next and repeat the process. Note that you may get a similar
reaction if you have the earth and the signal pins wrong. The indicator to see which one is
which is to see which pin reacts the most to the iron pulse. That pin is the signal output and the
other one the earth.
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