Doosan G20P-5, Service Manual, Page: 170 / 306

G424F(FE) Service Manual Chapter 5. Engine Management System (EMS) 168
Oxygen Sensor (Pre-Catalyst)
Component Location
Pre - Catalyst Oxygen Sensor
Description
The heated oxygen sensor is mounted on the front
side of Catalytic Muffler, which detects the oxygen
concentration in the exhaust gas. The heated
oxygen sensor produces a voltage that varies
between 0V and 1V. When the air/fuel ratio is lean,
the oxygen concentration in the exhaust gas
increases and the front HO2S outputs a low voltage
(approximately0~0.1V). When the air/fuel ratio is
rich, the oxygen concentration in the exhaust gas
decreases and the front HO2S outputs a high
voltage (approximately0.8~1V). The ECM constantly
monitors the HO2S and increases or decreases the
fuel injection duration by using the HO2S signal,
which is called closed-loop fuel control operation.
Specification
Temperature Temperature
(
℃
) (
℉
)
Front
HO2S
Heater
Resis-
tance( Ω )
(
℃
) (
℉
)
Front HO2S
Heater
Resistance
( Ω )
20 68 9.2 400 752 17.7
100 212 10.7 500 932 19.2
200 392 13.1 600 1,112 20.7
300 572 14.6 700 1,292 22.5
Schematic Diagram
[CIRCUIT DIAGRAM]
[HARNESS CONNECTORS]
C16
HO2S (B1/S1)
ECM HO2S (B1/S1)
After Main Relay
4
3
1
2
B13 - HO2S SIGNAL
B1 - HO2S GND
A23 - HO2S HEATER
(B1/S1)
2 1
4 3
Signal Wave Form
If you release the accelerator pedal suddenly after
engine running about 2600 rpm, fuel supply will stop
for short period and the O2 sensor service data will
display values 200mV or lower. When you suddenly
press on the accelerator pedal down, the voltage will
reach 0.6 ~ 1.0 V. When you let the engine idle
again, the voltage will fluctuate between 200 mV or
lower and 0.6 ~ 1.0 V. In this case, the O2sensor
can be determined as good.