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.
Checking current from HO2S under detecting condition,if the heater current is below a certain threshold for more than predeterminate time, ECM sets P0036. MIL(Malfunction Indication Lamp) turns on when the malfunction lasts till consecutive 2 driving cycle.
Item | Detecting Condition | Possible Cause |
DTC Strategy |
•
Monitor the current through the heater | 1. Poor Connection 2. HO2S(B1/S2) 3. ECM |
Enable Conditions |
•
Engine Running > 60 sec.
•
Heater Duty Cycle > 40%
•
Max. Duty Cycle - Min. Duty Cycle < 5% | |
Threshold value |
•
Filtered Heater Current < threshold value | |
Diagnosis Time |
•
Continuous (More than 2.5 second failure for every 5 second test ) | |
MIL On Condition |
•
2 Driving Cycles |
Condition | Current(A) |
Heater Current at 13.5V, 450℃(842°F) Exhaust | 0.52 ± 0.1 |
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.
