The normal operating temperature of the HO2S(Heated Oxygen Sensor) ranges from 350 to 850°C(662 to 1562°F). The HO2S heater greatly decreases the amount of time required for fuel control to become active. The ECM provides a pulse width modulated control circuit to adjust current through the heater. When the HO2S is cold, the value of the resistance is low and the current in the circuit is high. On the contrary, if the temperature in the resistor of the sensor rises, the current drops gradually.
When ECM detects short to ground in the heater control circuit(B2S1), ECM sets DTC P0051.
Item | Detecting Condition | Possible Cause |
DTC Strategy |
•
Power stage diagnosis |
•
Poor Connection
•
Short to ground in control circuit
•
B2S1 |
Enable Conditions |
•
- | |
Threshold value |
•
Short to ground | |
Diagnosis Time |
•
Continuous | |
MIL On Condition |
•
2 Driving Cycles |
Heater | |
Resistance (Ω) | 8.1 ~ 11.1 Ω at 21℃(69.8℉) |
Fig.1) The signal waveforms of front HO2S(the lower) and heater(the upper) at idle
The output voltage of front HO2S is changed continuously accroding to air/fuel ratio, ECM controls fuel amount based on this value. Preheating is necessary for HO2S normal operation. Therefore heater unit is installed in HO2S, ECM can control air/fuel ratio with the output signal of HO2S simultaneous with engine run by reducing preheating time. ECM controls heater with duty cycle. HO2S' power source is main relay and ECM operates heater by ground control.
