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.
DTC Descriptors
This diagnostic procedure supports the following DTCs:
| • | DTC P2297 HO2S Performance During Decel Fuel Cut-Off (DFCO) Bank 1 Sensor 1 |
| • | DTC P2298 HO2S Performance During Decel Fuel Cut-Off (DFCO) Bank 2 Sensor 1 |
Conditions for Running the DTC
Condition 1
| • | Before the ECM can report DTC P2297 or P2298 failed, DTCs P0030, P0031, P0050, P0051, P0052, P0130, P0131, P0132, P0150, P0151, P0152, P2237, P2240, P2243, P2247, P2251, and P2254 must run and pass. |
| • | The engine is operating. |
| • | The front HO2S are at operating temperature. |
| • | The desired front HO2S is less than 1.6 lambda. |
| • | The internal ECM HO2S signal voltage is less than 4.81 volts. |
| • | The fuel injectors are enabled. |
| • | DTC P2297 and P2298 runs continuously once the above conditions are met. |
Condition 2
| • | A decel fuel cut-off has occurred 10 times with successful adjustments. |
| • | DTC P2297 and P2298 runs continuously once the above conditions are met. |
Conditions for Setting the DTC
Condition 1
The ECM detects that the internal HO2S signal voltage is more than 3.7 volts for more than 10 seconds.
Condition 2
If the ECM detects that the compensation factor of the HO2S is less than -25 percent or more than 30 percent of the expected value, this DTC sets.
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. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step determines if a condition exists.
-
An HO2S that is not installed into the exhaust system causes this DTC to set.
Step | Action | 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 | |
Did DTC P2297 or DTC P2298 fail this ignition? | Go to Step 4 | Go to Step 3 | |
3 |
Does the DTC fail this ignition cycle? | Go to Step 4 | Go to Intermittent Conditions |
Is the heated oxygen sensor (HO2S) securely installed into the exhaust system? | Go to Step 5 | Go to Step 6 | |
5 | Test for shorted terminals and for poor connections at the HO2S. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 8 | Go to Step 7 |
6 | Install the sensor into the exhaust system. Refer to the appropriate procedure: Is the action complete? | Go to Step 8 | -- |
7 | Replace the HO2S. Refer to the appropriate procedure: Did you complete the replacement? | Go to Step 8 | -- |
8 |
Did the DTC fail this ignition? | Go to Step 2 | Go to Step 9 |
9 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | System OK | |
