P0031
DTC P0031CIRCUIT DESCRIPTION
Heating elements inside the heated oxygen sensor (HO2S) minimize the time required for the sensors to reach operating temperature and provide an accurate voltage signal. A low side driver within the engine control module (ECM) is pulse width controlled to provide variable current to the heater elements. During warm-up the ECM will reduce the ON time to prevent thermal shock to the sensor components from moisture in the exhaust system. The ECM will not allow full HO2S heating until calibrated limits of time, temperature, and intake airflow have been reached. The ECM periodically monitors the HO2S heater operating state by briefly turning OFF the heater low side driver at regular intervals. A small reference voltage is present at the heater low control circuit. When the low side driver is commanded ON, the reference voltage is low. When the low side driver is commanded OFF, the reference voltage is high, close to battery voltage. If the ECM detects that the HO2S heater low control circuit voltage is below 2.5 volts when the heater is commanded OFF, DTC P0031 will set for bank 1 sensor 1 or DTC P0051 will set for bank 2 sensor 1.
CONDITIONS FOR RUNNING THE DTC
- The engine is running.
- The Battery Voltage parameter is 10.5-17.3 volts.
CONDITIONS FOR SETTING THE DTC
The ECM detects that the HO2S heater low control circuit voltage is below 2.5 volts when the heater is commanded OFF, indicating a HO2S heater circuit shorted to ground.
ACTION TAKEN WHEN THE DTC SETS
- The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
- The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.
CONDITIONS FOR CLEARING THE MIL/DTC
- The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
- A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
- A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
- Clear the MIL and the DTC with a scan tool.
TEST
