Isuzu 4HK-1 and 6HK-1 Engine Sensor Locations
1. Engine coolant temp (ECT) sensor
The 2 wire engine coolant temperature sensor is located on the thermostat housing at the right front corner of the engine. The coolant sensor’s temperature detection component uses a thermistor. A 5 volt reference voltage is applied at all times to the sensor from the ECM. The ECM detects a voltage change due to a resistance value change in the sensor caused by the coolant temperature change.
2. Common rail pressure sensor
The common rail pressure sensor detects the common rail internal pressure. The common rail pressure sensor is installed to the common rail. As the common rail internal pressure changes depending on engine condition, output voltage of the common rail pressure sensor will change (if the common rail internal fuel pressure is low, output voltage becomes low, if the pressure is high, the output voltage becomes high as well). The engine control module (ECM) reads this output voltage change, converting it into common rail internal pressure, to utilize for control. Dedicated communication circuits are used for the sensor power supply (5V), SIG, and ground in the common rail pressure sensor, which are connected to the ECM. Also, the sensor circuit is shielded to avoid electrical noise etc.
3. Engine oil pressure sensor
The 3 wire engine oil pressure sensor is located on the left side of the engine just below and forward of the high pressure injection pump.
4. Crankshaft (CKP) Sensor
The 2 wire crankshaft position sensor (CKP) is located on the flywheel housing at the left rear corner of the engine. The CKP sensor detects 45 projections equally spaced every 7.5° around the flywheel periphery. There is also a space (equal to 3 projections) to act as a top dead center (TDC) reference signal for the engine control module (ECM). With these 45 pulses and the TDC reference signal, the ECM calculates the engine speed and exact position of the crankshaft.
5. Camshaft (CMP) Sensor
The 2 wire camshaft position sensor (CMP) is located on the cylinder head at the rear of the camshaft gear. The camshaft position sensor detects a total of the number of the cylinders in the engine plus an extra one. The extra hole indicates the top dead center position of number 1 cylinder. Five through holes (four holes arranged equally every 90° on the gear and one reference hole) on the camshaft gear flange surface on the 4HK-1 Engine. Seven through holes (six holes arranged equally every 60° on the gear and one reference hole) on the camshaft gear flange surface on the 6HK-1 Engine. The camshaft position sensor indicates the rotational position of the camshaft to the ECM. The CMP signal input, determines the crank angle and the ECM can use it to control fuel injection and calculate the engine speed. The crankshaft position sensor (CKP) typically controls these functions, however it is done by CMP sensor if the CKP sensor is faulty.
6. EGR valve
The 4 wire Exhaust Gas Recirculation (EGR) position sensor is installed in EGR valve and detects the valve lift amount of EGR.
Note: Do not disassemble the EGR position sensor. If it is faulty, replace it as EGR valve assembly.
7.Suction control valve (SCV)
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.
8. Fuel temperature (FT) sensor
The 2 wire variable resistor fuel temperature sensor is installed on the fuel supply pump. The fuel temperature sensor measures the temperature of the drain fuel from the pump. When the fuel temperature sensor is cold, the sensor resistance is high. When the fuel temperature increases, the sensor resistance decreases. With high sensor resistance, the ECM detects a high voltage on the signal circuit. With lower sensor resistance, the ECM detects a lower voltage on the signal circuit.
9. Boost temperature sensor
The 2 wire boost temperature sensor is installed onto the EGR valve on the upstream side of intake manifold. The sensor is a thermistor type. The resistance in the sensor changes as the temperature changes. When the intake temperature sensor is cold, the sensor resistance is high. When the intake temperature increases, the sensor resistance decreases. With high sensor resistance, the ECM detects a high voltage on the signal circuit. With lower sensor resistance, the ECM detects a lower voltage on the signal circuit.
10. Boost pressure sensor
The 3 wire boost pressure sensor is located in the piping to the intake manifold of the engine. The sensor converts the boost pressure into the voltage signal and sends it to engine control module (ECM). The ECM should detect a higher signal voltage at a high boost pressure.
The injectors are controlled by the engine control module (ECM). The ECM sends a common power supply to injectors 1, 3 and 5. The ECM also sends a common power supply to injectors 2, 4 and 6. The ECM fires the injectors by controlling the ground of the individual injectors. The ECM calculates the basic injection amount and timing based on the signals from throttle position sensor, boost pressure sensor, crankshaft (CKP) sensor, camshaft (CMP) sensor, etc. The timing of the injection is controlled by when the injector activates. The fuel quantity delivered is based upon the amount of time that the injector is open and also the pressure supplied by the common rail. To improve combustion in cylinders, the system injects a little fuel (pre- injection or pilot injection) and ignites it at the beginning of the cycle. A second injection (main injection) delivers the fuel required deliver the horsepower needed.
12. Glow plug
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.
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