Isuzu 4HK-1, Manual, Page: 10 / 50

10
Isuzu 4HK-1 and 6HK-1 Engine Overview (continued)
Inputs to 81 pin engine harness connector: (continued)
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The CAN (Controller Area Network) Data Bus Connector transmits communication
between the engine controller and the Excavator controller. This connector
transmits throttle, idle up/down, work mode, breaker mode, tachometer,
instrumentation and fault code information.
•
The memory clear (X23), diagnostic switch (X24) and data link (X4) connectors are
not used with the Case Electronic Service Tool (EST) diagnostic system. They are
required when using the Tech 2 Diagnostic Tool.
Outputs from 81 pin engine harness connector:
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When the ignition signal is present from the keyswitch, the ECM activates the main
relay. Once the Main Relay (K33 on machine schematic) is activated, battery power
is fed to the ECM through the relay normally open (NO) contacts to pins number 2
and 6. When the key switch is turned to the off position, the ECM continues to hold
the main relay activated for a period of time to allow the ECM to power down safely.
This delay is about 10 seconds.
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The glow control relay system consists of the ECM, glow relay, glow plug. When the
key switch is turned ON with low engine coolant temperatures, the ECM determines
the glow time and operates the glow relay (K2). After a certain time has elapsed, the
ECM will turn the glow relay to “OFF”. Also, after-glow function allows to stabilize
idling immediately after starting.
Outputs from 40 pin engine harness connector:
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The engine driven high pressure injection pump pressurizes fuel to feed to the
common rail. The injection pump has a suction control valve (SCV), and a fuel
temperature (FT) sensor. The suction control valve (SCV) is installed onto high
pressure pump section and controls supply of fuel (discharge amount) to common
rail. The engine control module (ECM) regulates period of electrical activation time of
the SCV to regulate the fuel discharge amount.
Do not replace the SCV. If it is faulty, replace it as supply pump ASM.
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The exhaust gas recirculation (EGR) system recirculates a part of the exhaust gas to
the engine intake to reduce the combustion temperature inside the cylinders to
reduce NOx (nitrogen oxides) in the exhaust gas. The EGR valve opening is
calculated according to the engine coolant temperature (ECT), the engine speed,
and the target fuel injection quantity.
The EGR motor is the brushless DC motor,
and is driven by three phases. The ECM drives the EGR motor through the EGR
motor drive circuits U, V, and W. The motor rotates with a combination of the three-
phase signals. The ECM sets the Error Code when the EGR motor drive duty is
high and the difference between the target EGR position and actual EGR position is
large.