Engine JAC HFC4DA1-2C. Manual - part 20

Maintenance manual for sunray hfc4da1-2c china-IV diesel engines 

 

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4) Malfunction Mode 

z  Short-circuit or open-circuit of sensor;   

z  Distorted, error, and suspicious signal;   

z  Unstable sensor signal;   

z  Sensor signal is out of range.   

5) Troubleshooting 

Use diagnosis instrument to check the trouble code and determine the malfunction position. Mainly check whether the 
sensor is installed in place and whether the clearance is normal, check the sensor circuit whether there is short-circuit 
or open-circuit to grounding wire, check whether there is short-circuit or open-circuit to the power supply, and check 
whether the circuit is consistent with the given pin definition.   

3. Pressure difference sensor 

1) Overview   

z  The pressure difference sensor is functioned to real-time monitor the pressure drop of the POC and determine 

whether the after-treatment system is working normally. The pressure at two ends of the POC is introduced via 
two pressure ports of the sensor and then the sensor converts the measurement into voltage value and feeds back 
to control unit. This can not only guarantee the sufficient oxidization of grains, but also prevent the blockage of 
catalytic converter.   

z  The pressure difference sensor and the POC are connected via stainless steel pipe and high temperature rubber 

hose. The pressure is introduced via stainless steel pipe, which is at least 250mm in length, from two sides of 
POC and then is led to the pressure difference sensor via high temperature rubber hose, which is capable of 
enduring more than 150ºC.   

2) Working Principle 

 

Maintenance manual for sunray hfc4da1-2c china-IV diesel engines 

 

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3) Test analysis   

Wiring terminals: 1 - +5V, 2 – Signal +, 3 – Grounding   

 

3.  Turbocharger pressure sensor   

1) Overview   

The turbocharger pressure sensor is connected to the 
intake pipe and is functioned to measure the absolute 
pressure of the intake pipe. This sensor is composed of 
one pressure unit with two sensing units and one 
evaluation circuit chamber. The sensing units and 
evaluation circuit are mounted on common ceramic 
substrate. Each sensing unit incorporates one horn-shaped 
diaphragm embodying the benchmark capacity for 
determination of internal pressure. The diaphragm moves 
towards large or small open extent as a function of 
charging pressure. The pressure sensitive resistor is 
mounted on the diaphragm surface, of which the resistance 
varies under the application of pressure. These resistors are 
connected to form a resistor bridge. Therefore, any 
movement of the diaphragm will change the balance of 
resistor bridge, namely the voltage of the resistor bridge is 
one measurement of turbocharger pressure. The evaluation 
circuit is functioned to amplify the bridge voltage and 
compensate the linear variation of temperature influence 
and pressure characteristic. The output signal of evaluation 
circuit is transmitted to ECU and then the turbocharger 
pressure is obtained by means of the programming 
characteristic curve.   

z  The temperature sensor incorporates one negative 

temperature coefficient (NTC) thermistor that is 
connected in the voltage division circuit of 5V power 
supply.  

z  The voltage drop on the resistor is inputted to the ECU via one analog and one digital converters (ADC), which 

is one measurement for evaluating the temperature. The ECU micro-processor embodies one characteristic curve, 
which defines the temperature as a function of given voltage.   

z  It’s installed on the pressure stabilizing chamber of intake manifold and take the priority to measure the pressure.   

z  Wiring terminals: 1 – Grounding, 2 – Temperature signal, 3 – +5V, 4 – Pressure signal.   

2) Working Principle 

The turbocharger pressure sensor is connected in the intake pipe and is capable of measuring the absolute pressure of 
intake pipe at 0.5~3bar. This sensor is composed of one pressure unit with two sensing units and one evaluation circuit 
chamber. The sensing units and evaluation circuit are mounted on common ceramic substrate. Each sensing unit 
incorporates one horn-shaped diaphragm embodying the benchmark capacity for determination of internal pressure. 
The diaphragm moves towards large or small open extent as a function of charging pressure. The pressure sensitive 

Pressure 

difference 

sensor 

5V power supply 

Pressure difference signal

Earthing

Maintenance manual for sunray hfc4da1-2c china-IV diesel engines 

 

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resistor is mounted on the diaphragm surface, of which the resistance varies under the application of pressure. These 
resistors are connected to form a resistor bridge. Therefore, any movement of the diaphragm will change the balance 
of resistor bridge, namely the voltage of the resistor bridge is one measurement of turbocharger pressure. The 
evaluation circuit is functioned to amplify the bridge voltage and compensate the linear variation of temperature 
influence and pressure characteristic. The output signal of evaluation circuit is transmitted to ECU and then the 
turbocharger pressure is obtained by means of the programming characteristic curve.   

The voltage drop on the resistor is inputted to the ECU via one analog and one digital converters (ADC), which is one 
measurement for evaluating the temperature. The ECU micro-processor embodies one characteristic curve, which 
defines the temperature as a function of given voltage.   

3) Measurement analysis  
Wiring terminals: 1 – Grounding, 2 – Temperature signal, 3 – +5V, 4 – Pressure signal.   

 

4) Malfunction Mode 

The light-up of the engine malfunction indicator lamp indicates the presence of malfunction in the engine system and 
it’s necessary to diagnose with diagnosis instrument. Use Sunray special diagnosis instrument to communicate with 
ECU of electronic injection system and read out the malfunction data in the ECU. 

5) Troubleshooting   

Use Sunray special diagnosis instrument to check the trouble code and determine whether there is short-circuit or 
open-circuit between circuit of malfunction position and the grounding wire, whether there is short-circuit or 
open-circuit to power supply, and whether the circuit is consistent with the given pin definition.   

4.  Thermal diaphragm air flowmeter   

1)   Overview   

z  The thermal diaphragm airflow sensor is one air mass sensor fitted with 

logic output. To obtain the air flow, the sensor diaphragm on the sensor is 
heated by the heating resistor installed in the middle and the temperature 
distribution on the diaphragm is measured by the temperature resistors 
installed paralleling with the heating resistor. The air flow passing through 
the sensor changes the temperature distribution on the diaphragm to cause 
resistance difference between two temperature resistors. The resistance 
difference depends on the direction and flow rate of the airflow so that the 
airflow sensor has high requirements over the flow rate and direction of the 
airflow. The sensor manufactured by micro-machinery features small size, 
low thermal capacity, and <15ms response time.   

z  The sensor is internally fitted with intake temperature sensor to measure the 

intake temperature.   

z  The air flowmeter is installed at the port of the air cleaner.   

z  Wiring terminals: 1. +12V power supply; 2. Grounding; 3. Air temperature signal; 4. Airflow rate signal.   

Turbocharger pressure 

and temperature 

sensor 

Grounding

5V power supply

Intake pressure signal

Intake temperature signal

Maintenance manual for sunray hfc4da1-2c china-IV diesel engines 

 

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2) Working Principle 

This sensor is composed of two sensors, namely airflow sensor and intake temperature sensor, and is installed on the 
intake hose after the air cleaner. This type of sensor requires that there shall be free of air leakage from the sensor to 
the engine combustion chamber, or it will lead to unstable idling of engine or even engine flameout.   

The airflow sensor integrates some micro-electronic units on a ceramic substrate. When the engine is working, the 
diaphragm will be heated. The intake airflow passing through the diaphragm will take away the heat and the 
Wheatstone bridge integrated on the diaphragm will increase the current to supplement the heat loss, which leads to 
the variation of electric signal. This signal is transmitted to the engine control unit ECU, based on which the ECU can 
obtain the load variation of the engine and thus control the fuel injection pulse width.   

The intake temperature sensing unit is one negative temperature coefficient (NTC) thermistor. The sensor installs two 
same sensing units on two sides of the thermal diaphragm. When the intake airflow flows through the diaphragm, the 
temperature of the temperature sensing unit on the front of diaphragm is slightly lower than that of temperature 
sensing unit on the rear. Based on this characteristic, the ECU can judge the direction of airflow.   

 

 

 

 

 

 

 

 

 

 

3) Measurement analysis   

Wiring terminals: 1. +12V power supply; 2. Grounding; 3. Air temperature signal; 4. Airflow rate signal.   

 

4) Malfunction Mode 

The subsequent electronic device of the air flowmeter in the ECU can judge the malfunctions such as open-circuit or 
short-circuit of internal circuit and connecting circuit of air flowmeter and the damage of sensor. Upon the detection 
that the output signal of the sensor is out of its output characteristic curve, the ECU will judge as malfunction of 
sensor.  

5) Troubleshooting   

When the airflow sensor is failed, the engine cooling fan will run at high speed for one period after the ignition key is 
turned to Off. For instance: When the airflow rate is higher than the upper limit of airflow or less than the lower limit 
of airflow, the ECU will judge as malfunction of sensor (Though the intake airflow rate is less than lower limit 
(closing to zero) at the start of the vehicle, the ECU can judge the start condition) and at the same time light up the 
engine malfunction lamp and work under malfunction mode.   

Air flowmeter 

Voltage output V

 

Common rail 

pressure