For 1990-2009 cars

### Circuit Description

The wide band heated oxygen sensor (HO2S) measures the amount of oxygen in the exhaust system and provides more information than the switching style HO2S. The wide band sensor consists of an oxygen sensing cell, an oxygen pumping cell, and a heater. The exhaust gas sample passes through a diffusion gap between the sensing cell and the pumping cell. The engine control module (ECM) supplies a voltage to the HO2S and uses this voltage as a reference to the amount of oxygen in the exhaust system. An electronic circuit within the ECM controls the pump current through the oxygen pumping cell in order to maintain a constant voltage in the oxygen sensing cell. The ECM monitors the voltage variation in the sensing cell and attempts to keep the voltage constant by increasing or decreasing the amount of current flow, or oxygen ion flow, to the pumping cell. By measuring the amount of current required to maintain the voltage in the sensing cell, the ECM can determine the concentration of oxygen in the exhaust. The HO2S voltage is displayed as a lambda value. A lambda value of 1 is equal to a stoichiometric air fuel ratio of 14.7:1. Under normal operating conditions, the lambda value will remain around 1. When the fuel system is lean, the oxygen level will be high and the lambda signal will be high or more than 1. When the fuel system is rich, the oxygen level will be low, and the lambda signal will be low or less than 1. The ECM uses this information to maintain the correct air/fuel ratio.

Fuel trim biasing is used by the ECM to keep the post catalyst HO2S voltage within a range of 580-665 mV as possible. This allows optimal catalyst efficiency under light load conditions, such as at idle or a steady cruise. The ECM constantly monitors how lean or rich the fuel trim bias is commanded. If the ECM detects that the fuel trim bias is commanded rich for more than a calibrated amount, DTC P2097 or P2099 sets.

### DTC Descriptors

This diagnostic procedure supports the following DTCs:

• | DTC P2097 Post Catalyst Fuel Trim System High Limit Bank 1

• | DTC P2099 Post Catalyst Fuel Trim System High Limit Bank 2

### Conditions for Running the DTC

• | Before the ECM can report DTC P2097 or P2099 failed, DTCs P0030, P0031, P0032, P0041, P0050, P0051, P0052, P0101, P0131, P0132, P0135, P0137, P0138, P0140, P0141, P0151, P0152, P0155, P0157, P0158, P0160, P0161, P2231, P2234, P2237, P2240, P2243, P2247, P2251, P2254, P2270, P2271, P2273, P2626, and P2629 must run and pass.

• | The engine is running.

• | The post catalyst fuel trim control and the rear HO2S vibrator are enabled for 40 seconds.

• | The front and rear HO2S are in closed loop.

• | The rear HO2S vibrator check is complete.

• | Disable the rear HO2S adjust--express dilution correction.

• | Disable the rear HO2S adjust--express enrichment correction.

• | There is no malfunction in HO2S lean transition.

• | The rear HO2S vibrator check is normal.

• | DTC P2097 and P2099 run continuously once the above conditions are met for more than 2 seconds.

### Conditions for Setting the DTC

The post catalyst fuel trim correction factor is biased rich by more than 3 percent of the HO2S lambda value for more than 4 seconds.

### Action Taken When the DTC Sets

• | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.

• | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

### Conditions for Clearing the MIL/DTC

• | The control module turns OFF the malfunction indicator lamp (MIL) at the beginning of the fourth ignition cycle, after 3 ignition cycles that the diagnostic runs and does not fail.

• | A current DTC, Last Test Failed, clears when the diagnostic runs and passes.

• | A history DTC and related Freeze Frame data clears after 40 warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

• | Clear the MIL and the DTC with a scan tool.

### Diagnostic Aids

• | Use the J 35616-A/BT-8637 Connector Test Adapter Kit for any test that requires probing the ECM harness connector or a component harness connector.

• | The lower connector of the ECM is connector C1 and the upper connector of the ECM is connector C2. Refer to Engine Controls Component Views .

• | For an intermittent condition, refer to Intermittent Conditions .

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. This step determines if a condition exists.

2. This step is testing for a rear HO2S sensor circuit condition. A circuit condition sets this DTC.

3. This step inspects for the rear sensors being connected to the correct bank of the engine. This condition causes this DTC to set.

4. This step is testing for an intermittent circuit condition. Thoroughly inspect the HO2S circuits for an intermittent circuit condition.

5. This step is testing for an intermittent circuit condition. Thoroughly inspect the HO2S circuits for an intermittent circuit condition.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 | Caution: Refer to Road Test Caution in the Preface section.

1. Allow the engine to reach operating temperature.

Important: The rear heated oxygen sensors (HO2S) must be in Closed Loop for this diagnostic to run. A road load condition is necessary to obtain Closed Loop.

2. Operate the vehicle within the parameters specified in Conditions for Running the DTC.
3. Observe the diagnostic trouble code (DTC) information with a scan tool.

Did DTC P2097 or DTC P2099 fail this ignition?

--

Go to Step 4

Go to Step 3

3 |

1. Observe the Freeze Frame/Failure Records for this DTC.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 4

Go to Diagnostic Aids

4 | Is DTC P0041, P0137, P0138, P0140, P0157, P0158, or P0160 also set? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle | Go to Step 5
5 |

1. Operate the engine above 1,200 RPM for 30 seconds.
2. Observe the appropriate rear heated oxygen sensor (HO2S) voltage with a scan tool.

Is the voltage less than the specified value?

1,050 mV

Go to Step 8

Go to Step 6

6 |

1. Turn OFF the ignition.
2. Disconnect the appropriate HO2S.
3. Turn ON the ignition, with the engine OFF.
4. Observe the HO2S voltage parameter with a scan tool.

Is the voltage within the specified range?

350-550 mV

Go to Step 13

Go to Step 7

7 | Test the appropriate HO2S signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 20 | Go to Step 15
8 | Inspect the rear HO2S for being connected to the correct bank of the engine. If the sensors are connected to the incorrect bank, swap the connectors as necessary. Did you find and correct the condition? | -- | Go to Step 20 | Go to Step 9
9 | Move the related HO2S harnesses for the front sensor between the HO2S harness connector and the engine control module (ECM) while monitoring the appropriate HO2S lambda parameter. Does the HO2S parameter change abruptly while moving the related harnesses? | -- | Go to Step 16 | Go to Step 10
10 | Move the related HO2S harnesses for the rear sensor between the HO2S harness connector and the ECM while monitoring the appropriate HO2S voltage parameter. Does the HO2S parameter change abruptly while moving the related harnesses? | -- | Go to Step 16 | Go to Step 11
11 |

1. Turn OFF the ignition.
2. Disconnect the HO2S.
3. Inspect the front and rear HO2S for the following conditions:

• | Damaged wiring between the HO2S and the ECM--An intermittent circuit condition may cause this DTC to set.

• | Terminal corrosion or water intrusion in the HO2S harness connectors

• | The correct terminal tension

• | The HO2S is securely installed.

• | Any exhaust leaks--Refer to Symptoms - Engine Exhaust .

4. Repair as necessary. Refer to Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 20

Go to Step 12

12 |

1. Disconnect the ECM.
2. Test the appropriate front HO2S circuits for being shorted together between the HO2S connector and the ECM. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 20

Go to Step 14

13 | Test for shorted terminals and for poor connections at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 20 | Go to Step 18
14 | Test for shorted terminals and for poor connections at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 20 | Go to Step 17
15 | Test for shorted terminals and for poor connections at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 20 | Go to Step 19
16 | Repair the circuit as necessary. Refer to Wiring Repairs . Did you complete the repair? | -- | Go to Step 20 | --
17 | Replace the HO2S. Refer to the appropriate procedure:

• | Heated Oxygen Sensor Replacement - Bank 1 Sensor 1

• | Heated Oxygen Sensor Replacement - Bank 2 Sensor 1

Did you complete the replacement?

--

Go to Step 20

--

18 | Replace the HO2S. Refer to the appropriate procedure:

• | Heated Oxygen Sensor Replacement - Bank 1 Sensor 2

• | Heated Oxygen Sensor Replacement - Bank 2 Sensor 2

Did you complete the replacement?

--

Go to Step 20

--

19 | Replace the ECM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 20 | --
20 |

1. Clear the DTCs with a scan tool.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 21

21 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle | System OK