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Lexus A/F and O2

This bulletin applies to 2007-2010 Lexus ES350 and RX350 models. Some vehicles may exhibit a MIL on DTC P0138 and/or P0158 (oxygen sensor circuit high voltage bank 1 or 2). In some instances, a P2195 or P2197 (A/F sensor signal stuck lean) DTC may also be present.

This condition may be caused by incorrect air fuel ratio sensor response. Additionally, a P0606 (ECM/PCM processor) DTC may be present due to incorrect oxygen sensor operation.

1. Check all DTCs. Are DTCs other than P0138 or P0158 present? If P2195 and/or P2197 are present, go to Step 3. If P0606 is present, go to Step 4. If no DTCs other than P0138 or P0158 are present, go to Step 2.

2. Check the A/F and O2 sensor values for the appropriate bank DTC freeze frame data. If the A/F voltage B#S1 = 3.35-3.70V, and the O2 B#S2 = 0.70-0.90V, replace the appropriate bank A/F ratio sensor only (not O2 sensor) to correct the P0138 or P0158 condition. If A/F sensor and O2 sensor values are not as specified above, inspect the O2 B#2 circuit for open, short or high resistance. If no trouble is found, refer to TIS and repair manual for P0138/P0158 diagnosis.

3. Inspect the air fuel ratio sensor for the appropriate bank. Does the air fuel ratio sensor have an open or short on the A1A+ or A1A- wires? If yes, repair the harness and re-evaluate the air fuel ratio sensor operation. Confirm that the previous DTCs do not reset. If no, replace the applicable bank air fuel ratio sensor only to correct the P2195/P0138 or P2197/P0158 condition.

4. Inspect oxygen sensor 2 freeze frame data values. Is the O2S B#S2 voltage more than 1.10V and/or the O2 sensor impedance B#S2 more than 300 ohms when the engine is at normal operating temperature?

  • Yes: Inspect O2 B#S2 circuit for open, short or high resistance. If no harness issues are found, replace the appropriate bank O2 sensor only to correct the P0606 DTC.
  • No: Follow the repair manual diagnostic procedure for P0138/P0158.

If the MIL on condition continues to occur after this procedure, refer to the repair manual for further diagnostic procedures and specifications.

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