NOTE:
Refer to “HOW TO CHECK TERMINAL” in GI-21 to probe or
check terminal.
TESTING FOR “OPENS” IN THE CIRCUIT
NBGI0004S0303
Before you begin to diagnose and test the system, you should
rough sketch a schematic of the system. This will help you to logi-
cally walk through the diagnosis process. Drawing the sketch will
also reinforce your working knowledge of the system.
SGI846
Continuity Check Method
The continuity check is used to find an open in the circuit. The
Digital Multimeter (DMM) set on the resistance function will indicate
an open circuit as over limit (no beep tone or no ohms symbol).
Make sure to always start with the DMM at the highest resistance
level.
To help in understanding the diagnosis of open circuits please refer
to the schematic above.
1)
Disconnect the battery negative cable.
2)
Start at one end of the circuit and work your way to the other
end. (At the fuse block in this example)
3)
Connect one probe of the DMM to the fuse block terminal on
the load side.
4)
Connect the other probe to the fuse block (power) side of SW1.
Little or no resistance will indicate that portion of the circuit has
good continuity. If there were an open in the circuit, the DMM
would indicate an over limit or infinite resistance condition.
(point A)
5)
Connect the probes between SW1 and the relay. Little or no
resistance will indicate that portion of the circuit has good con-
tinuity. If there were an open in the circuit, the DMM would
indicate an over limit or infinite resistance condition. (point B)
6)
Connect the probes between the relay and the solenoid. Little
or no resistance will indicate that portion of the circuit has good
continuity. If there were an open in the circuit, the DMM would
indicate an over limit or infinite resistance condition. (point C)
Any circuit can be diagnosed using the approach in the above
example.
Voltage Check Method
To help in understanding the diagnosis of open circuits please refer
to the previous schematic.
In any powered circuit, an open can be found by methodically
checking the system for the presence of voltage. This is done by
switching the DMM to the voltage function.
1)
Connect one probe of the DMM to a known good ground.
2)
Begin probing at one end of the circuit and work your way to
the other end.
3)
With SW1 open, probe at SW1 to check for voltage.
HOW TO PERFORM EFFICIENT DIAGNOSIS FOR AN ELECTRICAL INCIDENT
Circuit Inspection (Cont’d)
GI-28