Section IV. UNIT TROUBLESHOOTING.
4-9. TROUBLESHOOTING INTRODUCTION.
This section contains step by step procedures for identifying, locating, and isolating trailer equipment malfunctions.
4-10. TROUBLESHOOTING SYMPTOMS.
The first part of this section explains the use of the Troubleshooting Logic Tree. The last part of this section contains
the System Symptom Index (Table 4-2) which lists common malfunctions by trailer systems and the Troubleshooting
Trees (Table 4-3).
4-11. INTRODUCTION TO LOGIC TREE TROUBLESHOOTING.
Page Layout. Troubleshooting is divided into symptoms peculiar to a trailer system or component, for
example, air system or inversion valve.
Determine the symptom or condition that indicated a problem or failure. Refer to the System Symptom
Index, Table 4-2.
Go to the referenced page to begin troubleshooting. Open the manual flat so both the right and left pages
are displayed before you. The information on all facing pages is important.
All diagnostic logic and flowcharts are on the left-hand page, with supporting information, warnings,
cautions, notes, and test instructions on the right-hand page. Pages are setup so you do not need anymore
than the necessary information, warnings, cautions, and notes about a particular question. The
experienced technician generally reads just the left-hand page and refers to information on the right-hand
page when needed: all critical information for decision making is on the left-hand page.
How to Begin Troubleshooting.
Identify the symptom or fault.
Follow the diagnostic procedure. Answer Question No. 1 on the left-hand page and follow the YES or
NO path to either the remedy or the next page. Helpful information about the problem is also on the
left-hand page. Look on the right-hand page for additional specific instructions.
Observe WARNINGS, CAUTIONS, and NOTES. If you see the WARNING symbol on the left-hand
page, look on the right-hand page for the text of the warning. The warning message on the right-hand
page will also have the symbol above it. If you see the CAUTION symbol on the left-hand page, look
on the right-hand page for the text of the caution. The caution message on the right-hand page will also
have the symbol above it. If you see the NOTE symbol on the left-hand page, look on the right-hand
page for the text of the note. The note message on the right-hand page will also have the symbol above it.
Measurements Required for Troubleshooting.
Connect red test lead to Volt-Ohm input connector and black lead to COMMON (COM) input
connector on meter.