Engine JAC HFC4DA1-2C. Manual - part 21

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

5. Rail pressure sensor

1) Overview

The resistance of the metal film installed on the diaphragm will change accordingly following the change of shape.
This change of shape generated by the established system pressure (approximate 1mm under 1,500bar pressure) will
change the resistance and lead to the change of voltage between two sides of 5V bridge composed of resistor units.
This voltage change range is 0~70mv (depending on the applied pressure) and is amplified to 0.5~4.5V by the
evaluation circuit.
The accurate measurement of rail pressure is of great importance to the effective working of the system. This is one of
the causes for very strict tolerance over the rail pressure sensor during the pressure measurement. Under the scope of
main working conditions, the measurement accuracy is approximately ±2% of the full scale reading.

Wiring terminals: 1. Grounding; 2. Rail pressure sensor signal; 3. +5V power supply.

2) Working Principle

It transmits one voltage signal to the ECU, depending on the fuel pressure. The rail pressure sensor must measure the
instant pressure in the fuel rail and embody sufficient accuracy and rapid response capability. The rail pressure sensor
is composed of following parts:
cIntegrated sensing unit welded onto the pressure device
d Printed circuit board (PCB) with electric evaluation circuit
sensor housing with electric connector. The fuel flows into the rail pressure sensor via one hole on the common rail
and the end of this hole is sealed by one sensor diaphragm. The fuel under high pressure reaches the sensor diaphragm
via one blind hole. One sensing unit (semiconductor unit) is arranged on this diaphragm and converts the pressure into
electric signal. This signal generated is transmitted via wire to evaluation circuit, which will amplify this signal and
transmit to the ECU.

3) Test analysis

Wiring terminals: 1 - Grounding; 2 - Rail pressure sensor signal; 3 - +5V power supply.

4) Malfunction Mode

The malfunction indicator lamp lights up if the voltage is higher or less than this limit. If the voltage is out of the
normal working voltage range, but is not out of the limit, the malfunction indicator lamp will not light up.

5) Troubleshooting

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 JAC special diagnosis instrument to communicate with ECU
of electronic injection system and read out the malfunction data in the ECU.

6. Engine coolant temperature sensor

1) Overview

z The sensor is installed on the cylinder head, closing to the water outlet. The body is made of brass to protect the

resistor unit fabricated from negative temperature coefficient (NTC) resistor;

Rail

pressure

sensor

5V power supply

Rail sensor signal

Grounding

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

z The temperature resistor of the temperature sensor is one part of the 5V

voltage division circuit. Two terminals of the temperature sensor is
connected with the voltage charged circuit. When the temperature
resistor of the temperature sensor changes along with the temperature,
the voltage of the voltage charged circuit changes accordingly, which
will be inputted to the analog/digital conversion circuit of ECU
interface circuit. The relationship characteristic curve between voltage
and temperature is stored in the ECU of engine management system;

z Sunray is equipped with 3-wire water temperature sensor to save the

cost and guarantee the system unity.

2) Working Principle

The coolant temperature sensor is used to measure the working temperature of the engine. The ECU will provide the
engine with best control scheme, depending on different temperatures.

This sensor is one negative temperature coefficient (NTC) thermistor, of which the resistance reduces following the
increasing of coolant temperature in a non-linear mode. The negative temperature coefficient thermistor is installed
within one copper heat conducting sleeve. By means of one voltage division circuit, the ECU converts the resistance
change of thermistor to one varying voltage and provides to the ECU and thus monitors the change of water
temperature (internal structure of ECU).

3) Measurement analysis

Wiring terminals: 1 – Temperature signal; 2 – Grounding

Reference values: -10℃ 8.642---10.152 kΩ

20℃2.351---2.649 kΩ

80℃0.313---0.332 kΩ

4) Malfunction Mode

Upon the detection that the water temperature signal is higher or less than the limit range, the ECU will light up the
malfunction indicator lamp.

5) Troubleshooting

Sunray is fitted with one independent coolant temperature sensor to transmit the water temperature signal to the
instrument for display of instrument water temperature alarm. If the water temperature alarm indicator lamp lights up,
stop for cooling immediately. If the water temperature alarm indicator lamp lights up frequently, drive to the
authorized service station of JAC Multifunctional Commercial Vehicle Company for service.

7. Water level sensor

1) Overview

z The fuel-water separator position sensor is functioned to measure the water content in the fuel filter;

z When the water content reaches a predefined level, the ECU will control the working of the engine. This sensor

is installed on the bottom of the fuel filter;

Characteristic curve of temperature sensor

Resi

Temperature

Water

temperature

sensor

To water temperature gauge

Signal terminal

Grounding

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

z The fuel-water separator position sensor is installed on the bottom of the fuel filter;

z Wiring terminals: 1. Water level sensor; 2. Water level signal; 3. +12V power supply.

2) Working Principle

The grain substances are high-accuracy filtered by means of the interception and absorption of the filter medium and
the water concentrated on the filter medium is
separated by gravity force. The water separated
is deposited in the water chamber at the lower
portion of filter housing.

The water level sensor is installed at the lower
portion of water chamber. When the water level
reaches the sensing point of the sensor, the
internal circuit of sensor is actuated to output
signal to the ECU. At the same time, the signal is
transmitted to the instrument to light up the
water level alarm lamp.

3) Measurement analysis

Wiring terminals: 1 - Water level sensor; 2 - Water level signal; 3 - +12V power supply.

4) Malfunction Mode

z Short-circuit or open-circuit of sensor;

z Unstable sensor signal;

z Sensor signal is out of range.

1) Troubleshooting

Use Sunray special diagnosis instrument to check the trouble code and determine the malfunction position. Mainly
check the circuit of sensor and determine whether there is short-circuit or open-circuit between circuit 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.

8. Accelerator pedal position sensor

1) Overview

The accelerator pedal position sensor is mounted on
the accelerator pedal.

The accelerator pedal position sensor and the
accelerator pedal form one integral part. The
accelerator pedal position sensor internally
incorporates two same potentiometer sensors to
provide the driver’s driving demand signal to the ECU.
This process is completely same with the presently
mechanical pedal in terms of operation, in order to
adapt to the years of driving habit of the driver. Two
same sensors provide the accelerator signal to the
ECU respectively, which guarantees more safety and reliability of the system.

Wiring terminals: 1. +5V; 2. +5V; 3. Grounding of accelerator pedal 1; 4. Signal of accelerator pedal 1; 5. Grounding
of accelerator pedal 2; 6. Signal of accelerator pedal 2.

Signal terminal of

fuel-water separator

position sensor

Water level sensor of

fuel-water separator

Output vo

ltage

Full close

Full open

Open angle of accelerator pedal

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

2）Working Principle

The accelerator pedal position sensor internally adopts the damping structure and internally incorporates two same
potentiometer sensors. The signal pointers of the sensors are coaxial with the pedal. When the accelerator pedal is
stepped down, the potentiometer pointer will rotate coaxially with the pedal and, following the sliding of the
potentiometer pointer, the signal terminals output different voltage or resistance signal. Two movable potentiometer
sensors with different resistances within the position sensor output different resistances. However, there is a defined
relationship between the resistances outputted by two sensors. The ECU adopts the voltage signals, instead of the
resistance signals of the sensor, in order to prevent the signal distortion caused by the voltage fluctuation of the
alternator. A comparison circuit is adopted to compare the signal voltage outputted by the sensor with the standard
voltage and the ECU adopts the comparison result to judge the movement amplitude of the pedal. The ECU compares
the signals inputted by the sensor 1 and sensor 2 and considers other sensors (engine speed, load, etc.) to jointly judge
the trueness of the signals outputted by the sensors. If the signal distortion is judged in any of two sensors, the ECU
controls the engine to actuate malfunction mode and adopt restrained driving measures.

The accelerator pedal position sensor provides one signal voltage varying along with the accelerator pedal position.
The engine control unit (ECU) will provide independent 5V reference voltage and low level reference voltage to each
accelerator pedal position sensor. When the accelerator pedal is stepped down, the signal voltage of the accelerator
pedal position sensor 1 is increased, namely from approximate 0.7V at the free position to above 4V at the fully
stepped down position. When the accelerator pedal is stepped down, the signal voltage of the accelerator pedal
position sensor 2 is increased, namely from approximate 0.3V at the free position to above 2V at the fully stepped
down position. Two data monitor mutually via control system.

3) Measurement analysis

Wiring terminals: 1 - +5V; 2 - +5V; 3 - Grounding of accelerator pedal 1; 4 - Signal of accelerator pedal 1; 5 -
Grounding of accelerator pedal 2; 6 - Signal of
accelerator pedal 2.

Working voltage of sensor: 5V

Malfunction Mode

Short-circuit or open-circuit of sensor 1;

Short-circuit or open-circuit of sensor 2;

Unstable sensor signal;

Sensor signal is out of range.

4) Troubleshooting

Characteristic of sensor internal structure: Two potentiometer sensors within the sensor adopt independent power
supply and independent grounding wire, which can guarantee the system safety. When one sensor is damaged, another
sensor can still work. However, the engine system has already actuated the malfunction mode in such case and the
electronic control system will adopt the restrained driving measures.

9. Vehicle speed sensor

1) Overview

The vehicle speed sensor is located at the rear portion of the transmission and is mainly functioned to provide speed
signal to the engine control unit and instruments.

Accelerator

pedal

module

Power supply of sensor 1

Signal 1

Power supply of sensor 2

Signal 2

Grounding of sensor 2

Grounding of sensor 1

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