P0031

Diagnostic Chart:

Schematic:

The heated oxygen (HO2S) bank 1 sensor 1 is threaded into the cylinder 1, 3, 5 exhaust manifold (cylinders 1, 3, 5 are closest to front of dash). The sensor is equipped with a heater to decrease the amount of time to enter closed loop fuel control for bank 1. The ECM controls the heater by supplying a ground to circuit 5038. The ECM will pulse the heater until it has determined exhaust pipe moisture has evaporated (engine run time between 0 and 30 seconds). After that, the ECM will command the heater On at a 100% duty cycle for 10 seconds, after which it will turn Off the heater for a very short amount of time to test for an open/low voltage condition. The ECM will continue to do this unless the exhaust gas temperature exceeds 850°C (1562°F). The heater will be pulsed if this limit is exceeded. 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 (2.6-4.6 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 cranking/running.

DTC PARAMETERS
DTC P0031 will set if HO2S bank 1 sensor 1 heater feedback voltage is less than 2.6 volts when heater is commanded Off when:
^ Condition exists for longer than 0.5 seconds
^ Engine speed is greater than 40 rpm
^ Main relay voltage is between 8.0 and 18.0 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 Scan tool to monitor DTC P0031 LAST TEST just after the engine is started. The ECM will pulse the heater On and Off from anywhere between 0 and 30 seconds, then the ECM will turn it Off briefly every 10 seconds. Wiggling wires while watching for a change from PASSED to FAILED during the Off command may locate the area where a short to ground in the wiring may exist.

Heater element resistance: 7.0-20.2 ohms