117 

 

No.065 Fuel pressure regulator DR   

 

 
 
 
 
 
 
 
 
 
 
 
 
 

• Function: For oil return system, fuel pressure regulator is used for regulating fuel pressure of 
fuel system, making difference with pressure of intake manifold kept at a constant value.   
 
• Principle: This pressure regulator is diaphragm type overflow valve. when system fuel pressure 
is increased, oil pressure within oil inlet exceeds resultant force of pre-tightening force of the 
spring and air pressure within spring chamber, the diaphragm will be jacked, and valve will be 
opened. Fuel is returned to fuel tank through oil return port in center of pressure regulator, and 
fuel pressure dropped, till the valve is closed.     
• Mounting position: 

 

  Installed at fuel distribution pipe for oil return system.   

 
 
Malfunction: Fuel pressure too low or too high, difficult to startup, etc.   
 
General causes: Due to uses of poor quality fuel, it will cause: 1. blocked filter screen; 2. foreign 
substances causing large leakage. In addition, manually mechanical damages, etc. Maintenance 
precautions: during maintenance: 1. do not impact diaphragm element by high pressure gas; 2. 
do not clean it with strong corrosive liquid; 3. deformation is not allowed due to outside force.   
Simple measuring method: For oil return system, connect fuel pressure gauge at oil sucker, and 
start the engine, making it operate at idling speed status. Fuel pressure of the engine shall be 
around 260kPa at this time; take out vacuum tube of fuel pressure regulator, and fuel pressure 
shall be around 300kPa at this time. 

 
 

 

 

118 

Diagnosis flowchart of fuel regulation 

 

1. With the engine running at 1200rpm under normal temperature, 

check voltage of oxygen sensor displayed is kept at lower than 0.275V 

with the diagnosis instrument?   

2. Remove joint of oxygen sensor, and check its voltage is between 

0.35-0.55V with the engine under idling speed?   

3. Check two lines connecting oxygen sensor (10-3; 28-4) are with 

open circuit, shorted to ground or shorted to voltage source?   

4. Check voltage of oxygen sensor displayed is kept larger than 0.75V 

with the diagnosis instrument?   

5. Remove joint of oxygen sensor, and its voltage is lower than 0.35V 

with the diagnosis instrument?   

6. Remove oxygen sensor     

7. Repair short circuit or open circuit   

Completed 

To troubleshooting tip 

Y 

Y 

Y 

Y 

N 

N 

N 

N 

N 

REPAIR 

 
 

 

 

119 

 

No.066 Oxygen sensor LSH   

 
 
 
 
 
 

1

 

cable conductor，  2 disk washer, 3 insulating bushing, 

4

 

protective sleeve, 5 clamping connector of heating 

element 
6 heating rod, 7 contact gasket  8 sensor seat, 9 
ceramic probe, 10 protective tube 

• 

Function: Measure oxygen contents of engine exhaust, and determine gasoline and air are 

fully burnt. And electronic controller realizes closed-loop control using excess air coefficient =1 
as the goal according to this information, to ensure maximum conversion efficiency of three-way 
catalytic converter on three pollutants such as HC, CO and Nox from the exhaust.   

• 

Principle: Sensing element is ceramic tube, to exhaust externally and to atmosphere internally. 

When temperature of sensing ceramic tube reaches 350 , it is with solid electrolyte. With this 

℃

feature, convert concentration difference of oxygen to potential difference, reaching output of 
electrical signal. If mixture gas is too thick, concentration difference of oxygen in and out of 
ceramic tube is high, and potential difference is also high. And a great amount of oxygen is 
moved from inner side to outer side, and output voltage is high (close to 900mV); if mixture gas is 
too thin, concentration difference of oxygen in and out of ceramic tube is low, and potential 
difference is also low. And only a small amount of oxygen is moved from inner side to outer side, 
and output voltage is low(close to 100mV). 
Mounting position: Installed at front of exhaust pipe. 
  Malfunction: poor idling speed, poor acceleration, tail gas exceeding standard, oil consumption 
too large, etc. 
Installation torque: 40~60  N•M 
General causes: 1. wet water vapor enters to inner of sensor, and temperature changes 
suddenly and probe is broken; 2. oxygen sensor “poisoning”.( Pb, S, Br, Si ).   
Maintenance precautions: do not use cleaning liquid, oily liquid or volatile solid at oxygen sensor 
during maintenance. 
Simple measuring method: 
  (remove the connector) Place digital multimeter to ohm position, and two pens are respectively 
connected to 1# (white), 2# (white) pins of sensor, and resistance is 1~6Ω under normal 
temperature.  

 

(connect the connector) under idling speed status, when oxygen sensor reaches working 
temperature of 350 , place digital multimeter to DC voltage 

℃

position, and two pens are 

respectively connected to 3# (grey, 4# (black) pins of sensor, and voltage shall fluctuate quickly 
between 0.1-0.9V. 

 
 

 

 

120 

Diagnosis flowchart of oxygen sensor 
 

 

 

 

1. Connect the diagnosis instrument, and start the engine to water temperature ＞
80℃. Observe voltage of sensor signal is between 0.2-0.8?   

2. Check two lines connecting oxygen sensor (sensor 4-ECU28, sensor 3-ECU10) 
are with open circuit, shorted to ground or power source (＞1.098V for shorted to 
power source,  ＜0.092 for shorted to ground) 

3. Close ignition, and plug in controller. Connect voltmeter to two white conductors of 
oxygen sensor, and the engine is started and running at idling speed, and check 
value displayed at voltmeter is between 12-14V?   

4. Close ignition and remove connection of socket connector of oxygen sensor. 
Connect two white conductors of oxygen sensor with multimeter, and check resistance 
is between 0.5-20ohm? Note: this value is related to temperature.   

5. Close ignition and remove connection of socket connector of oxygen sensor. 
Measure resistance of signal line (black) and signal cathode conductor (grey) of the 
sensor is within the following range:  ＞30MΩ at -20℃;  ＞10MΩ at 350℃;  ＞100KΩ at 
850℃.  

6. Close ignition and take out controller plug. Remove connection of socket connector 
of oxygen sensor, and connect the multimeter, and check resistance of cathode 
conductor is  ＜0.5Ω?  

7. Steps same as 6; connect the multimeter to another terminal, andcheck resistance 

of anode conductor is  ＜0.5Ω?  

8. Close ignition, plug in controller, and remove connection of socket connector of 

oxygen sensor. Connect black and central earthing with the voltmeter, with ignition 
turned on. Observe reading of voltmeter is between 0.4-0.6V?   

Replace oxygen sensor, and confirm repairs   

Replace ECU 

Completed 

Repairs  

Y 

Y

Y

Y 

Y 

Y

Y

N

N 

N

N

N 

N 

N 

N

No