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.
If the ECM detects short to battery in heater under detecting conditions, ECM sets P0038. MIL(Malfunction Indication Lamp) turns on when the malfunction lasts till consecutive 2 driving cycle.
Item
Detecting Condition
Possible Cause
DTC Strategy
Detects a short to battery
Poor Connection
Short to battery in control circuit
HO2S(B1/S2)
ECM
Enable Conditions
No disabling Faults
Engine Running
11V = Battery Voltage = 16V
Threshold value
Short to battery
Diagnosis Time
Continuous (More than 5 seconds failure for every 10 seconds test )
MIL On Condition
2 Driving Cycles
Heater
Resistance (?)
8.1 ~ 11.1 ? at 21?(69.8?)
Fig.1) The signal waveforms of front HO2S(the lower) and heater(the upper) at idle
Fig.2) The signal waveforms of rear HO2S(the upper) and heater(the lower) at idle
Fig.3) The Normal data of HO2S heaters at idle
Fig.4) The data of HO2S heaters at open condition in HO2S(B2S1) circuit
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.