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 open in the heater control circuit(B2S1), PCM sets DTC P0050.
Item
Detecting Condition
Possible Cause
Case1
DTC
Strategy
Heater current check
Poor connection
Open or Short to ground in power circuit
Open in control circuit
B2S1
Enable
Conditions
350C < temp(EGT around Upstream O2S (model)) < 550C
IAT > -7C
10.7V < B+ volt < 16.1V
Threshold
Value
Internal resistance > threshold f(cat. temp., heater power)
Diagnostic
Time
15 sec
Case2
Power stage diagnosis
-
Heater check open
Continuous
MIL ON Condition
2 driving cycle
Fig.1) The signal waveforms of front 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.