For 1990-2009 cars

One function of the heated oxygen (HO2S) bank 2 sensor 2 is to determine the amount of fuel trim biasing (the HO2S bank 2 sensor 2 is threaded into the front exhaust pipe directly behind the cylinder 2, 4, 6 pre-converter). Fuel trim biasing is the slight rich or lean fuel control adjustment the ECM performs during cruising conditions based on engine operating parameters intended to keep the HO2S bank 2 sensor2 voltage at a target 660 mV. The fuel trim bias adjustment is designed to be centered around a lambda value of 1.000 (14.7 to 1 A/F ratio). If the lambda value from the HO2S bank 2 sensor 1 is greater than 1.000 needed to achieve the HO2S bank 2 sensor 2 target voltage, the ECM is commanding slightly lean. If the lambda value is less than 1.000 in order to achieve the HO2S bank 2 sensor 2 target voltage, the ECM is commanding slightly rich. The ECM will continuously run a check to make sure the fuel trim bias adjustment is within limits. DTC P0152 will set if the fuel trim bias adjustment is too far above or below the 1.000 HO2S bank 2 sensor 1 lambda reading in order to achieve a 660 mV HO2S bank 2 sensor 2 target voltage. This indicates that the ECM has exceeded its lean or rich fuel trim bias limit threshold which infers that the HO2S bank 2 sensor 1 signal voltage has shifted up or shifted down.

### DTC Parameters

DTC P0152 will set if the lambda value from the HO2S bank 2 sensor 1 (actual measured A/F ratio where 14.7 to 1 equals lambda value of 1.000) indicates greater than 1.030 or less than 0.970 in order to achieve a 660 mV HO2S bank 2 sensor 2 target voltage when:

• | The condition exists for longer than 100 seconds.

• | The bank 2 loop status is closed.

• | The HO2S bank 2 sensor 2 loop status is closed.

• | The HO2S bank 2 sensor 2 DTCs have not been set.

DTC P0152 diagnostic runs continuously once the above conditions have been met.

P0152 is a type B DTC.

### Diagnostic Aids

Important: If another HO2S bank 2 sensor 1 circuit or slow response DTC; or if an HO2S bank 2 sensor 2 circuit or slow response DTC is set, diagnose that DTC first.

Make sure no exhaust leaks exist between the bank 2 engine head and 18 inches after the HO2S bank 2 sensor 2.

A short to ground or a short to voltage on any HO2S non-heater circuit will display 3.999 for the HO2S BANK 2 SENSOR 1 lambda value on the scan tool. An open input pump current or reference ground circuit will display 1.000 for the HO2S BANK 2 SENSOR 1 lambda value on the scan tool.

Start engine and allow the ECT to reach at least 80°C (176°F). Using the scan tool, monitor the HO2S BANK 2 SENSOR 2. Make sure the reading is not consistently below 400 mV or consistently above 900 mV. If the reading is consistently lower than 400 mV, refer to DTC P0157 flowchart. If the reading is consistently above 900 mV, refer to the DTC P0158 flowchart. The reading should be within the 500 mV to 800 mV range. If the reading is OK, the most probable cause for DTC P0152 is a weak, aging or contaminated HO2S bank 2 sensor 1. Check for obvious contamination, such as oil, fuel or engine coolant by removing sensor. Source and fix the cause of the contamination, if contaminated. Replace the HO2S bank 2 sensor 1.