In order to control the emission of the CO, HC and NOx components of the exhaust gas, a heated oxygen sensor (HO2S), mounted on the front side and rear side of the catalytic converter, detects the oxygen content in the exhaust gas. The front HO2S signal is used to control air/fuel ratio (closed loop fuel control) and the rear HO2S signal is used to monitor front HO2S and catalyst for proper operation. The HO2S requires a minimum temperature to operate properly and provide a closed loop fuel control system. So the HO2S contains a heater element to reduce warm-up time and ensure proper performance during all driving conditions, which allows for closed loop fuel control or catalyst monitoring immediately upon engine start-up. The ECM controls this heater element by duty cycle. The main relay supplies voltage to the heater and the ECMprovides a ground circuit for activating the heater.
ECM sets DTC P0031 if the ECM detects that the front HO2S heater control line is short to ground.
ECM sets DTC P0037 if the ECM detects that the rear HO2S heater control line is short to ground.
Item
Detecting Condition
Possible cause
DTC Strategy
-
? Open in battery and control circuit
? Short to ground in control circuit (pin 48 to 36)
? Faulty HO2S heate
? Faulty ECM
Threshold value
Enable Conditions
Diagnostic Time
? Continuous
HO2S Heater
Normal Parameter
20 ~ 24?(68°F ~ 75.2°F)
Heater Resistance
9?
This figure shows the waveform measured at terminal 3 of HO2S.
Point ? is the duration heater operates and the normal voltage is below 0.8V.
In case the output voltage is over 0.8V.
Possible cause:Poor ECM ground connection Or poor ECM connector’s connection
Point ? is the duration heater doesn’t operates and the normal voltage is battery voltage.