Circuit Inspection
INTRODUCTION
In general, testing electrical circuits is an easy task if it is approached in a logical and organized method. Before
beginning it is important to have all available information on the system to be tested. Also, get a thorough
understanding of system operation. Then you will be able to use the appropriate equipment and follow the
correct test procedure.
You may have to simulate vehicle vibrations while testing electrical components.Gently shakethe wiring
harness or electrical component to do this.
OPEN A circuit is open when there is no continuity through a section of the circuit.
SHORT There are two types of shorts.
+SHORT CIRCUITWhen a circuit contacts another circuit and causes the
normal resistance to change.
+SHORT TO GROUNDWhen a circuit contacts a ground source and grounds the
circuit.
TESTING FOR ``OPENS'' IN THE CIRCUIT
Before you begin to diagnose and test the system, you should rough sketch a schematic of the system. This
will help you to logically walk through the diagnosis process. Drawing the sketch will also reinforce your work-
ing knowledge of the system.
Continuity check method
The continuity check is used to ®nd an open in the circuit. The Digital Multimeter (DMM) set on the resistance
function will indicate an open circuit as over limit (OL, 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 in®nite resistance condition. (point A)
5. Connect the probes between SW1 and the relay. Little or no resistance will indicate that portion of the cir-
cuit has good continuity. If there were an open in the circuit, the DMM would indicate an over limit or in®-
nite 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 in®nite resistance condition. (point C)
Any circuit can be diagnosed using the approach in the above example.
SGI846
HOW TO PERFORM EFFICIENT DIAGNOSIS FOR AN ELECTRICAL INCIDENT
GI-24
NOTICE:
The ¯ow chart indicates work procedures required to diagnose
problems effectively. Observe the following instructions before
diagnosing.
1) Use the ¯ow chart after locating probable causes of a prob-
lem following the ``Preliminary Check'', the ``Symptom
Chart'' or the ``Work Flow''.
2) After repairs, re-check that the problem has been com-
pletely eliminated.
3) Refer to Component Parts and Harness Connector Loca-
tion for the Systems described in each section for
identi®cation/location of components and harness con-
nectors.
4) Refer to the Circuit Diagram for Quick Pinpoint Check.
If you must check circuit continuity between harness con-
nectors in more detail, such as when a sub-harness is
used, refer to Wiring Diagram in each individual section
and Harness Layout in EL section for identi®cation of har-
ness connectors.
5) When checking circuit continuity, ignition switch should
be ``OFF''.
6) Before checking voltage at connectors, check battery volt-
age.
7) After accomplishing the Diagnostic Procedures and Elec-
trical Components Inspection, make sure that all harness
connectors are reconnected as they were.
Example
AGI056
HOW TO FOLLOW FLOW CHART IN TROUBLE DIAGNOSES
GI-30
