Engine JAC HFC4DA1-2C. Service manual — part 22

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

87

2）Working Principle

The signal of vehicle speed sensor provides vehicle speed signal to the ECU, based on which the ECU calculates the
vehicle speed. It’s internally composed of one Hall speed sensor. Please refer to the camshaft position sensor for the
working principle.

3）Measurement analysis

10. Clutch switch

1) Overview

The clutch switch is located on the upper portion of the clutch pedal and is mainly functioned for cruise control and
engine torque smoothness control.

2) Working Principle

The clutch switch is installed at the clutch pedal and transmits the operation signal of clutch pedal to the engine ECU.
Its inside is one two-pin contact switch. When the clutch pedal is stepped down, the lower central position of the
clutch switch springs out. In such case, two pins of the clutch switch are connected. When the clutch pedal is released,
two pins of the clutch switch are disconnected. Therefore, the engine can learn the operation state of the driver by
measuring the electric level (high or low) of the clutch switch signal wire.

3) Measurement analysis

4) Malfunction Mode

Short-circuit or open-circuit of sensor;

Unstable sensor signal;

Sensor signal is out of range.

5) 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.

Input signal

of vehicle

speed sensor

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

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11.Dual brake switch

1) Overview

The dual brake switch is located on the upper portion of the brake pedal and internally incorporates two independent
switches.

2) Working Principle

The brake switch monitors the action of the brake pedal and transmits the signal measured to the engine ECU. The
brake switch is equipped with two switching mechanisms, which are the main and secondary units of the brake switch.
When the signals from both units are inputted, the engine ECU will judge as normal braking signal. These switching
signals are related to the accelerator pedal and are used to control the fuel amount during the braking. This means that
the operation of accelerator pedal will not lead to malfunction when the brake pedal is stepped down, but the operation
of accelerator pedal will reduce the fuel amount when the brake pedal is stepped down.

3) Measurement analysis

12. A/C switch

1) Overview

The A/C switch is located on the A/C control panel and is mainly functioned to transmit actuation directive of A/C
compressor to the engine control unit.

2). Working Principle

A/C request is the input signal that the driver requests the working of A/C and controls the working of A/C relay as
well as the speed promotion of the engine.

3) Measurement analysis

4) Malfunction Mode:

z Short-circuit or open-circuit of signal circuit;

z Unstable signal;

z The signal is out of range.

Low pressure

High pressure

A/C switch

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

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5) 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.

II. Engine control unit (ECU)

1) Overview

The engine control unit is located on the firewall on the
back of the bottom of the glove box.

2) Working Principle

The ECU has one metal housing and the sensors, actuators, and power supply are connected to the ECU via multi-pole
plug. The power supply parts for direct control of actuators are integrated in the ECU so that their heat can be
effectively expanded to the ECU housing.

Requirements for ECU are as below:

- Surrounding (ambient) temperature: -40ºC~+85ºC

- Resistance to fuel, lubricating oil, etc.

- Resistance to moisture.

- The mechanical load has high requirements of the exposure to electromagnetic compatible (EMC) signal.

The ECU is used to calculate the signal received from the external sensors and control at the allowable voltage level.
Based on these input data and stored characteristic graph, the microprocessor can calculate out the duration and
accurate moment for fuel injection and convert into time-signal curve. The specific accuracy requirement and high
dynamic response of engine require high level calculation capability.
The driver stage is actuated by means of the output signal and supplies proper power to the actuators to control the
common rail pressure and the high pressure pump units. In addition, the actuators can control the engine functions
(such as relays for exhaust gas recirculation actuator, turbocharger pressure actuator, and electronically controlled fuel
pump) and other auxiliary functions (such as fan relay, auxiliary heater relay, and electric heating plug relay, and air
conditioner). The driver stage has the short-circuit protection and the protection against damage due to current
overload. These types of malfunctions and the open-circuit will be reported to the microprocessor. The diagnosis
function of the fuel injector driver stage can identify the error signal curve occurred. In addition, one series of output
signal can be transmitted to other vehicle systems via different interfaces. Within the specific safety concept
framework, the ECU can monitor the entire injection system.
The actuation of fuel injector advances special requirements over the driver stage. Within the fuel injector, the current
from the driver stage generates one magnetic field force in the magnetic coil that applies onto the hydraulic high
pressure system. To ensure the accurate tolerance and high repeatability of the fuel injection amount, this coil must be
actuated in front of a steep current wave. This requires ECU to form high voltage.

The actuation time (fuel injection duration) can be classified by the current control circuit into start current stage and
holding stage. It must work accurately to ensure that the fuel injectors can guarantee the repeatability of fuel injection
under all working conditions. In addition, it must reduce the energy loss in the ECU and the fuel injectors.

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

90

3) Measurement analysis

Interface A

Interface K

Definition for ECU pins of EDC17 control system:

Terminal

No.

Description

Terminal

No.

Description

Interface A

A01

High fuel injector of 3

rd

cylinder

A31

Low fuel injector of 2

nd

cylinder

A02

High fuel injector of 2

nd

cylinder

A32

A03

A33

Low fuel injector of 4

th

cylinder

A04

Power supply of EGR actuator

A34

A05

A35

Earthing of camshaft position sensor

A06

5V power supply of rail pressure sensor

A36

A07

5V power supply of absolute pressure sensor

A37

High coolant temperature signal

Outlet

Outlet