Part 1 of 4
TROUBLESHOOTING PROCEDURESDiagnostic procedures for many of the circuits are included with
the schematics. These procedures are based on a logical problem-solving
procedure. The steps listed below are provided for those circuits that do
not include diagnostic procedures. Following these steps will enable you
to make a quick diagnosis of the problem.
1. Verify the Problem
Operate the problem circuit to check the accuracy of the complaint.
Note the symptoms of the inoperative circuit.
2. Analyze the Problem
Refer to the schematic of the problem circuit in the ETM. Determine
how the circuit is supposed to work by tracing the current path(s)
from the power feed through the circuit components to ground. Then,
based on the symptoms you noted in step 1 and your understanding of
circuit operation, identify one or more possible causes of the problem.
3. Isolate the Problem
Make circuit tests to prove or disprove the preliminary diagnosis made
in step 2. Keep in mind that a logical, simple procedure is the key to
efficient troubleshooting. Test for the most likely cause of failure
first. Try to make tests at points which are easily accessible.
4. Repair the Problem
Once the specific problem is identified, make the repair using the proper
tools and safe procedures.
5. Check the Problem
Operate the circuit to check for satisfactory circuit operation. Good
repair practice calls for rechecking all circuits you have worked on.
TROUBLESHOOTING TOOLS
Isolating the problem (Step 3 of TROUBLESHOOTING PROCEDURES) requires the
use of a voltmeter and/or ohmmeter. A voltmeter measures voltage at selected
points in a circuit. An ohmmeter measures a circuits resistance to current
flow. It has an internal battery that provides current to the circuit under
test. Disconnect the car battery when using an ohmmeter because the battery
voltage will cause the ohmmeter to give false readings. Also, do not use an
ohmmeter on solid state components. The voltage that the ohmmeter applies
to the circuit could damage these components.
System Troubleshooting Procedures:
Fused Jumper Wire
A jumper wire is made up of an in-line fuse holder connected to a set of test
leads. It should have a five ampere fuse. Use it for bypassing open circuits.
Never use a jumper wire across any load (motors, etc.). This direct battery
short will blow the fuse.