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 PCM 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 PCM detects short to ground in the heater control circuit(B2S2), PCM sets DTC P0057.
Item
Detecting Condition
Possible Cause
DTC Strategy
Power stage diagnosis
Poor connection
Short to ground in control circuit
B2S2
Enable Conditions
-
Threshold value
Short to ground
Diagnosis Time
Continuous
MIL On Condition
2 Driving Cycles
Heater
Resistance (?)
9.0 at 20?
Fig.1) The signal waveforms of rear HO2S(the upper) and heater(the lower) at idle
The output voltage of front HO2S is changed continuously accroding to air/fuel ratio, PCM controls fuel amount based on this value. Preheating is necessary for HO2S normal operation. Therefore heater unit is installed in HO2S, PCM can control air/fuel ratio with the output signal of HO2S simultaneous with engine run by reducing preheating time. PCM controls heater with duty cycle. HO2S' power source is main relay and PCM operates heater by ground control.