Power Probe IV User Manual page 20

Page 18
Advanced Testing Operations
Driver Testing
and may not energize the circuit. DRV TST provides a safe voltage supply to validate the circuit or the
driver inside the module without the relay or component installed.
Modern ECUs have circuits that let the ECU know if a component is actually plugged in, and the
driver circuit will not energize the circuit if no component is there. Also, in order for the computer
to detect output faults, like shorts or opens, the component being driven has to be within a specific
resistance range or the computer also will not energize the driver circuit. When the Power Probe IV
is in Driver Test Mode, it will provide the necessary voltage and pull-up resistance to ensure proper
driver testing. (see product specifications pg.19)
Power Probe IV
DRV TST = Driver Test Mode is design to test the
drivers (transistor) inside the module's (PCM, BCM, GEM,
etc.) control circuit.
More and more electrical components on modern vehi-
cles are being turned on and off by computer modules
or Electronic Control Units (ECUs). Many components,
such as transmission solenoids or fuel injectors, can be
switched directly from the ECU. Other high current com-
ponents, like radiator fans are operated thru relays which
are then controlled by the ECU. Special transistor circuits,
called driver circuits, are built in to these modules that
can supply, the current necessary to power these different
parts.
Driver circuits' current carrying capabilities are limited
and a shorted component that draws more current than it
should can overload the driver circuit and cause it to fail.
When testing the control signal to a component, relay or
solenoid, the module will need to have the voltage present
that the component normally would supply into the mod-
ule. If the component, relay or solenoid is unplugged the
module will no longer be able to pull the voltage to ground
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