TROUBLESHOOTING AND ELECTRICAL
SYSTEM: DIESEL VEHICLES
Test Procedures
12
TEST PROCEDURE 12 – Wire Harness Diodes
See General Warnings, Section 1, Page 1-2.
A diode is designed to conduct current in one direction only. Depending on the application, diodes are used in the
vehicle to control electrical system logic, or to help protect relay and switch contacts from excessive arcing.
See
following NOTE.
NOTE:
If a diode conducts current in both directions, the diode has failed closed. If a diode will not conduct current in
either direction, the diode has failed open
2m
20
m
200
m
2k
200
200
200
200
20
2
200
m
500
20k
200k
2000
k
1000
OFF
WAVETEK
5XL
V
V
V
A
!
!
COM
200nA
MAX
1000 ---
750V
FUSED
2m
20
m
200
m
2k
200
200
200
200
20
2
200
m
500
20k
200k
2000
k
1000
OFF
WAVETEK
5XL
V
V
V
A
!
!
COM
200nA
MAX
1000 ---
750V
FUSED
2m
20
m
200
m
2k
200
200
200
200
20
2
200
m
500
20k
200k
2000
k
1000
OFF
WAVETEK
5XL
V
V
V
A
!
!
COM
200nA
MAX
1000 ---
750V
FUSED
1. VOM Black Lead 2. VOM Red Lead 3. Wiring Diagram Symbol
with Diode Stripe Orientation 4. Good Diode (Probe Scenario A) -
Conducts Current and Shows Continuity 5. Good Diode (Probe
Scenario B) - No Continuity 6. Bad Diode - Meter Beeps In Either
Direction (Probe Scenarios A and B)
1127
Figure 12-20
Basic Diode Information
The wire harness is equipped with several in-line diodes. The following table describes each diode’s function in the
electrical system, the location in the wire harness, and the symptom(s) of a diode failure.
2016 Carryall 1500/1700 and XRT 1550 Maintenance and Service Manual
Page 12-25
Summary of Contents for Carryall 1500 2016
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