For 1990-2009 cars

The heated oxygen sensor (HO2S) bank 1 sensor 1 is threaded into cylinder 1, 3, 5 exhaust manifold (cylinders 1, 3 and 5 are closest to the front of the dash). The sensor monitors the oxygen content in the exhaust gas before the pre-converter. The ECM supplies a variable output pump current to circuit 1667 in order to maintain a constant voltage level at the input pump current 1665. 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 the 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 ration divided by 14.7 to 1) based on the input pump current voltage level on circuit 1665 and the signal voltage level on circuit 412. DTC P0133 will set if the ECM determines that the HO2S bank 1 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 P0133 will set, indicating the HO2S bank 1 sensor 1 is responding too slowly.

### DTC Parameters

DTC P0133 will set if the ECM comparison quality factor for the HO2S bank 1 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%.

• | HO2S bank 1 sensor 1 lamdba value is between 0.96-1.04.

• | The loop status bank 1 is closed.

• | There is no EVAP purge solenoid, EVAP system or fuel trim, or the misfire DTCs have been set.

The DTC P0133 diagnostic runs continuously once the above conditions have been met.

P0133 is a type B DTC.

### Diagnostic Aids

Make sure no corrosion is present in the HO2S bank 1 sensor 1 harness connector. Make sure no exhaust leaks exist between the bank 1 engine head and the HO2S bank 1 sensor 2. Each of these two conditions may set P0133.

The most probable cause for DTC P0133, is a weak, aging or contaminated sensor. Check for obvious contamination, such as oil, fuel or engine coolant, by removing the sensor. Source and fix the cause of the contamination if contaminated. Replace the HO2S bank 1 sensor 1.

Bank 1 will default to open the loop if this DTC is active.