The heated oxygen sensor (HO2S) bank 2 sensor 1 is threaded into the cylinder 2, 4, 6 exhaust manifold (cylinders 2, 4 and 6 are closest to the front of the radiator). The sensor monitors the oxygen content in the exhaust gas before the pre-converter. The ECM supplies a variable output pump current to circuit 1664 in order to maintain a constant voltage level at the input pump current circuit 1666. As output pump current passes through the oxygen sensor when the sensor is operating above 300°C (572°F), the sensor will vary resistance according to changes in exhaust oxygen content. If oxygen content increases (lean air/fuel ratio), the resistance of the sensor increases, which requires less current to maintain a constant voltage level. The ECM calculates a lambda value (actual air/fuel ratio divided by 14.7 to 1) based on the input pump current voltage level on circuit 1666 and the signal voltage level on circuit 1653. DTC P0151 will set if the ECM determines that the HO2S bank 2 sensor 1 response times for changing air/fuel ratios are becoming too long. The ECM compares the actual response times to modeled response times, then assigns a quality factor to the comparison. Once the quality factor drops below a calibrated threshold, DTC P0151 will set indicating the HO2S bank 2 sensor 1 is responding too slowly.
DTC Parameters
DTC P0151 will set when the ECM comparison quality factor for the HO2S bank 2 sensor 1 response test is below 60%, indicating a slow responding sensor when:
| • | The engine speed is between 1400-2520 RPM. |
| • | The engine load is between 23-45%. |
| • | The HO2S bank 2 sensor 1 lambda value is between 0.96-1.04. |
| • | The loop status bank 2 is closed. |
| • | There is no EVAP purge solenoid, EVAP system, fuel trim, or the misfire DTCs have been set. |
DTC P0151 diagnostic runs continuously once the above conditions have been met.
P0151 is a type B DTC.
Diagnostic Aids
Make sure no corrosion is present in the HO2S bank 2 sensor 1 harness connector. Make sure no exhaust leaks exist between the bank 2 engine head and HO2S bank 2 sensor. Each of these two conditions may set P0151.
The most probable cause for DTC P0151 is a weak, aging or contaminated sensor. Check for obvious contamination, oil, fuel or engine coolant, by removing the sensor. Source and fix the cause of the contamination, if contaminated. Replace the HO2S bank 2 sensor 1.
Bank 2 will default to open loop if this DTC is active.
