Circuit Description
The engine control module (ECM) supplies a voltage near 450 mV between the heated oxygen sensor (HO2S) high signal circuit and the low reference circuit. The HO2S varies the voltage over a range from about 1,000 mV when the exhaust is rich, down through about 10 mV when the exhaust is lean.
The ECM monitors and stores the HO2S voltage information. The ECM evaluates the HO2S voltage samples in order to determine the amount of time that the HO2S voltage was out of range. The ECM compares the stored HO2S voltage samples taken within each sample period and determines if the majority of the samples are out of the operating range. The ECM test for the following conditions:
| • | The ECM monitors the HO2S voltage to determine if the signal voltage goes below a predetermined threshold within a certain amount of time. If the ECM determines that the signal voltage remains above a threshold, the ECM commands a lean condition. If the signal voltage does not go below the threshold within a certain amount of time after commanding the system lean, this DTC sets. |
| • | The ECM monitors the HO2S voltage during fuel cut-off. If the ECM determines that the signal voltage is more than a predetermined voltage during fuel cut-off, this DTC sets. |
DTC Descriptors
This diagnostic procedure supports the following DTCs.
| • | DTC P2271 HO2S Signal Stuck Rich Bank 1 Sensor 2 |
| • | DTC P2273 HO2S Signal Stuck Rich Bank 2 Sensor 2 |
Conditions for Running the DTC
| • | Before the ECM can report DTC P2271 or P2273 failed, DTCs P0036, P0037, P0038, P0056, P0057, P0058, P137, P0138, P0140, P0141, P0157, P0158, P0160, P0161, P0342, P0343, P0367, P0368, P0366, P0443, P0451, P0452, P0453, P0458, and P0459 must run and pass. |
| • | The rear HO2S are at operating temperature for more than 10 seconds. |
| • | The fuel injectors are enabled. |
| • | The long term fuel control is enabled. |
| • | The mass air flow (MAF) sensor is between 6-33 g/s for the intrusive test. |
| • | The MAF sensor is more than 10 g/s. |
| • | DTC P2271 and P2273 runs continuously once the above conditions are met. |
Conditions for Setting the DTC
If the ECM detects that the rear HO2S voltage is more than 650 mV for more than 100 seconds, then an intrusive test is performed. The ECM will lean the fuel mixture up to -7 percent and then wait for 10 seconds at -7 percent. If the ECM detects that the HO2S voltage is still more than 650 mV, the ECM then test the HO2S at the next decel fuel cut-off. If the ECM detects the HO2S voltage is more than 200 mV after 4 seconds in decel fuel cut-off, 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) after 4 consecutive 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 clears after 40 consecutive 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 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 . |
| • | A fuel delivery condition causes this DTC to set. Thoroughly inspect all items that cause a rich condition. |
| • | For an intermittent condition, refer to Intermittent Conditions . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step determines if a condition exists.
-
This step is testing for a rear HO2S sensor circuit condition. A circuit condition sets this DTC.
-
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-Engine Controls? | -- | Go to Step 2 | |||||||||||||||
Did DTC P2271 or DTC P2273 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 Diagnostic Aids | ||||||||||||||
4 | Is DTC P0137, P0138, P0140, P0157, P0158, or P0160 also set? | -- | Go to Step 5 | |||||||||||||||
Is the voltage less than the specified value? | 1,050 mV | Go to Step 8 | Go to Step 6 | |||||||||||||||
6 |
Is the voltage within the specified range? | 350-550 mV | Go to Step 12 | Go to Step 7 | ||||||||||||||
7 | Test the appropriate HO2S signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 13 | ||||||||||||||
Move the related HO2S harnesses for the rear sensor between the HO2S harness connector and the engine control module (ECM) while monitoring the appropriate HO2S voltage parameter. Does the HO2S parameter change abruptly while moving the related harnesses? | -- | Go to Step 14 | Go to Step 9 | |||||||||||||||
9 |
Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 10 | ||||||||||||||
10 | Inspect for the following conditions:
Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 11 | ||||||||||||||
11 |
Important: When you have completed the fuel system diagnosis, return to this diagnostic. Test the fuel system for operating rich. Refer to Fuel System Diagnosis . Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 12 | ||||||||||||||
12 | Test for shorted terminals and for poor connections at the HO2S. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 15 | ||||||||||||||
13 | Test for shorted terminals and for poor connections at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 16 | ||||||||||||||
14 | Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 17 | -- | ||||||||||||||
15 | Replace the HO2S. Refer to the appropriate procedure: Did you complete the replacement? | -- | Go to Step 17 | -- | ||||||||||||||
16 | Replace the ECM. Refer to Engine Control Module Replacement . Did you complete the replacement? | -- | Go to Step 17 | -- | ||||||||||||||
17 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 18 | ||||||||||||||
18 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||||||||||
