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P0131

Diagnostic Chart:




Schematic:




The heated oxygen (HO2S) bank 1 sensor us threaded into the cylinder 1, 3, 5 exhaust manifold (cylinders 1, 3, 5 are closest to front of dash). The sensor is an electrical source that responds to oxygen content in the exhaust manifold. When the sensor reaches approximately 316°C (600°F), it is fully functional and produces a voltage based on the difference in oxygen between the atmosphere and exhaust gas. The ECM sends a 450 mV bias voltage on the signal line, which is pulled up through high resistance. When the HO2S bank 1 sensor 1 is cold, it produces no voltage and has extremely high internal resistance. The internal resistance of the sensor is much greater than the resistance of the bias pull-up resistor. However, when the sensor heats up, it produces voltage that overrides the bias voltage. This voltage is read by the ECM to determine a rich/lean HO2S bank 1 sensor 1 signal used to adjust injector pulse width. Under normal conditions, low sensor voltage means high oxygen content/lean air-fuel mixture and vice versa. Normal sensor readings will fluctuate between 60 mV and 1080 mV. DTC P0131 will set if the HO2S bank 1 sensor 1 signal voltage is too low for a certain length of time.

DTC PARAMETERS
DTC P0131 will set if HO2S bank 1 sensor 1 signal is less than 40 mV when.
^ Condition exists for longer than 10 seconds
^ HO2S bank 1 sensor 2 signal is greater than 499 mV
^ Exhaust pipe moisture has evaporated (calculated engine run time between 0 and 30 seconds), then engine must run for longer than 80 seconds
^ Commanded air/fuel ratio is 14.7 to 1
^ EVAP leak diagnostics are not running
^ Calculated exhaust gas temperature is less than 800°C (1472°F)
^ Main relay voltage is greater than 10.5 volts
^ No EVAP purge solenoid or EVAP flow during non-purge DTCs have been set

OR

HO2S bank 1 sensor 1 signal is less than 40 mV when:
^ Condition exists for longer than 0.1 seconds
^ HO2S bank 1 sensor 1 is determined to be COLD (inactive)

DTC P0131 diagnostic runs continuously once the above conditions have been met.

P0131 is a type B DTC.

DIAGNOSTIC AIDS
To locate an intermittent problem, use Scan tool to monitor HO2S BANK 1 SENSOR 1 voltage with ignition On, engine Off after the engine has cooled down. Wiggling wires while watching for a change from bias voltage (450 mV) may locate the area where a short to ground in the wiring may exist.

NOTE: A short to ground on the HO2S bank 1 sensor 1 signal low circuit 1653 will NOT affect the sensor signal circuit.