Isuzu N-Series. Manual — part 416
6D6-10 QOS II PREHEATING SYSTEM
EMISSION AND ELECTRICAL DIAGNOSIS 6E-1
ENGINE 4H SERIES
SECTION 6E (4HE1-TC/4HG1-T Only)
EMISSION AND ELECTRICAL DIAGNOSIS
Caution:
When fasteners are removed, always reinstall them at the same location from which they were removed. If a fastener
needs to be replaced, use the correct part number fastener for that application. If the correct part number fastener is
not available, a fastener of equal size and strength for (stronger) may be used. Fasteners that are not reused, and
those requiring thread locking compound, will be called out. The correct torque values must be used when installing
fasteners that require it. If the above conditions are not followed, parts or system damage could result.
Contents
GENERAL DESCRIPTION . . . . . . . . ... 6E-3
DIAGNOSIS (4HE1-TC Only) . . . . . . . . 6E-15
BRIEF EXPLANATION OF EMISSION AND ELECTRI-
CAL CONTROL SYSTEM. . . . . . . . ... 6E-35
6E-2 EMISSION AND ELECTRICAL DIAGNOSIS
Fast Idle Control Device (FICD) System Malfunction. .6E-145
SPECIAL TOOLS. . . . . . . . . . . .. 6E-148
DIAGNOSIS (4HG1-T Only). . . . . . . ..6E-150
Strategy-Based Diagnostics . . . . . . .. 6E-150
GENERAL SERVICE INFORMATION . . . .. 6E-151
EMISSION AND ELECTRICAL DIAGNOSIS 6E-3
GENERAL DESCRIPTION
The emission and electrical control system operates on
a 12 or 24 volt power supply with negative ground polar-
ity. Each wire in the vehicle is of a specific size and has
an identifying colored insulation.
These colors are indicated in wiring diagrams and will
help in tracing circuits and making proper connections.
Wire size is determined by load capacity and circuit
length. Some wires are grouped together and taped.
Such a grouping of wires is called a harness.
The harness use a split corrugated tube to protect the
wires from the elements. Each circuit consists of the fol-
lowing:
• Power source - the battery and the alternator.
• Wires - To carry electrical current through the cir-
cuit.
• Fuses - To protect the circuit against current over-
load.
• Relays - To protect voltage drop between the bat-
tery and the circuit parts and to protect the switch
points against burning.
• Switches - To open and close the circuit.
• Load - Any device, such as a light or a motor, which
converts the electrical current into useful work.
• Ground - To allow the current to flow back to the
power source.
In this manual, such electrical device is classified by
system. For major parts shown on the circuit based on
the circuit diagram for each system, inspection and re-
moval and installation procedures are detailed.
Notes for Working on Electrical Items
Battery Cable
Disconnecting the Battery Cable
1. All switches should be in the “OFF” position.
2. Disconnect the battery ground cable.
3. Disconnect the battery positive cable
4. Disconnect the battery cable (1).
Caution:
It is important that the battery ground cable be discon-
nected first.
Disconnecting the battery positive cable first can result
in a short circuit.
Connecting the Battery Cable
Follow the disconnecting procedure in the reverse or-
der.
Caution:
Clean the battery terminal and apply a light coat of
grease to prevent terminal corrosion.
Connecting Handling
Disconnecting the Connectors
Some connectors have a tang lock to hold the connec-
tors together during vehicle operation.
Legend
A. For 24 volt
1. Cable
Legend
A. For 12 volt
N6A1104E
N6A1105E
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