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