GxT Ferret 91 2-Channel Labscope - Manual (Page 9)

9
Sensor Tests
Intake Air Temp IAT
Connect COM probe to the sensor’s ground circuit, engine
block, or negative battery post. Connect the CH1 probe
to the sensor’s signal to the PCM. Spray the sensor tip
with cooling spray or begin the test at the suspected
temperature range and verify the signal’s amplitude is
within its limits for the given temperature. Opens will
appear as upward spikes to VRef. Shorts will appear as
downward spikes to ground.
Engine Coolant ECI
Connect COM probe to the sensor’s ground circuit, engine
block, or negative battery post. Connect the CH1 probe
to the sensor’s signal to the PCM. Begin the test at the
suspected temperature range, and verify the signal’s
amplitude is within its limits for the given temperature.
Opens will appear as upward spikes to VRef. Shorts will
appear as downward spikes to ground.
Fuel Temp. Sensor
Connect COM probe to the sensor’s ground circuit, engine
block, or negative battery post. Connect the CH1 probe
to the sensor’s signal to the PCM. Begin the test at the
suspected temperature range, and verify the signal’s
amplitude is within its limits for the given temperature.
Opens will appear as upward spikes to VRef. Shorts will
appear as downward spikes to ground.
Knock Sensor
Connect COM probe to the negative battery post or engine
block. Connect CH1 probe to the sensor output signal
circuit to the PCM (or spark control unit). With the key off,
lightly tap the engine (in the general vicinity of the sensor)
with something metallic. The amplitude of the oscillations
in the waveform should increase with harder taps.