The heated oxygen sensor (HO2S) bank 1 sensor 1 is threaded into the cylinder 1, 3, 5 exhaust manifold (cylinders 1, 3 and 5 are closest to front of the dash). The sensor is equipped with a heater element to decrease the amount of time required to enter the closed loop fuel control. The ECM controls the heater by pulsing circuit 751 to ground. When the heater is commanded Off (circuit not grounded), the voltage level at the ECM should be high (ignition voltage). When the heater is commanded On (circuit grounded), the voltage level at the ECM should be low. The ECM heater feedback circuit uses a pull-up voltage (1.6-3.6 volts), which allows the ECM to individually differentiate between an open, short to ground or short to voltage. DTC P0031 will set if the ECM detects lower than normal feedback voltage when HO2S bank 1 sensor 1 heater is commanded Off with the engine running.
DTC PARAMETERS
DTC P0031 will set if the HO2S bank 1 sensor 1 heater feedback voltage is less than 1.6 volts. The heater is commanded Off when:
| • | The condition exists for longer than 0.4 seconds. |
| • | The engine is running. |
| • | The battery voltage is between 11.0-15.0 volts. |
DTC P0031 diagnostic runs continuously once the above conditions have been met.
P0031 is a type B DTC.
DIAGNOSTIC AIDS
To locate an intermittent problem, use the scan tool to monitor the HO2S HEATER BN. 1 SEN. 1 with the engine running. The voltage should fluctuate greater than 1 volt, indicating the circuit is functioning correctly. Compare this parameter to the HO2S HEATER BN. 2 SEN. 1 parameter. Both parameters should closely match. The voltage will not change greater than 1 volt when a short to ground occurs.
Heater element resistance: 2.4-9.2 ohms
