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.
If the PCM detects short to ground or open in heater under detecting conditions, PCM sets P0037. 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 ground or open
? Poor Connection
? Open in Power Circuit
? Open or short to ground in control circuit
? HO2S(B1/S2)
? PCM
Enable Conditions
? No disabling Faults
? Engine Running
? 11V = Battery Voltage = 16V
Threshold value
? Short to ground or open circuit
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°F)
Fig1) The signal waveforms of front HO2S(the upper) and heater(the lower) at idle
Fig2) The signal waveforms of rear HO2S(the upper) and heater(the lower) at idle
The HO2S requires a minimum temperature to provide a closed loop fuel control system. So the HO2S contains a heater element to reduce its warm-up time and ensure its performance during all driving conditions. The PCM controls this heater element by duty cycle. The main relay supplies voltage to the heater and the PCM provides a ground circuit for activating the heater.