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 HO2S utilizes the following circuits:
| • | A signal circuit |
| • | A low reference circuit |
| • | An ignition 1 voltage circuit |
| • | A heater control circuit |
The ECM monitors the rich-to-lean transition time. A transition is defined as the HO2S voltage changes from above 600 mV to below 300 mV . If the ECM detects that the transition time is too long, the DTC sets.
DTC Descriptor
This diagnostic procedure supports the following DTCs:
| • | DTC P2096 Post Catalyst Fuel Trim System Low Limit Bank 1 |
| • | DTC P2098 Post Catalyst Fuel Trim System Low Limit Bank 2 |
Conditions for Running the DTC
| • | DTCs P0030, P0031, P0050, P0051, P0101, P0102, P0103, P0111, P0112, P0113, P0116, P:0117, P0118, P0119, P0121, P0122, P0123, P0125, P0128, P0131, P0132, P0134, P0151, P0152, P0154, P0171, P0172, P0174, P0175, P0261, P0262, P0263, P0264, P0265, P0266, P0267, P0268, P0270, P0271, P0273, P0274, P0276, P0277, P0300, P0400, P0401, P0402, P0403, P0404, P0405, P0406, P0441, P0442, P0444, P0445, P0455, P0456, P0501, P1171, P1172, P1174, P1175, P1504 are not set. |
| • | The H02S test is ran when the following conditions are met during decel fuel cut-off (DFCO) mode: |
| - | The engine is operating. |
| - | The engine coolant temperature is more than 75°C (169°F). |
| - | The ignition 1 voltage is more than 10 volts. |
| - | The post heated oxygen sensors are at operating temperature. |
| - | The fuel system is in closed loop. |
| - | The modeled catalyst temperature is more than 400°C (752°F). |
| - | The vehicle speed is more than 5 Km/h (3 mph) |
| • | The DTCs run continuously once the above conditions are met. |
Conditions for Setting the DTC
The ECM detects that the HO2S rich-to-lean transition time is more than the maximum predetermined transition time.
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 3 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. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step determines if the condition is present. This test may take 5-10 minutes for the diagnostic to run.
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This step tests the HO2S signal and the low reference circuit for an high resistance. The HO2S voltage should go low.
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An exhaust leak 6-12 inches away from the HO2S can cause a DTC to set.
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Certain RTV silicone gasket materials release vapors that can contaminate the HO2S. Silicone in the fuel can also cause silicone contamination. If the sensors appear contaminated by silicone, and if all the silicone sealant is a non-silicone base, advise the customer to try a different fuel company. A missing fuel filler restrictor indicates that the customer may have used leaded fuel.
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 | |||||||||||||||||
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Important: If any DTCs are set, except for P2096 or P2098, refer to those DTCs before proceeding with this diagnostic table.
Did the DTC P2096 or P2098 fail this ignition? | -- | Go to Step 4 | Go to Step 3 | |||||||||||||||||
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Intermittent Conditions | ||||||||||||||||
Is the voltage less than the specified value? | 20 mV | Go to Step 8 | Go to Step 5 | |||||||||||||||||
5 |
Is the voltage less than the specified value? | 20 mV | Go to Step 7 | Go to Step 6 | ||||||||||||||||
6 | Test the HO2S signal circuit for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 10 | ||||||||||||||||
7 | Test the HO2S low reference circuit for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 10 | ||||||||||||||||
Inspect for an exhaust leak near the oxygen sensor. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 9 | |||||||||||||||||
Inspect or test for the following conditions:
Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 11 | |||||||||||||||||
10 | Test for shorted terminals and for poor connections at the harness connector of the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and Repairing Connector Terminals in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 12 | ||||||||||||||||
11 | Replace the appropriate HO2S. Did you complete the replacement? | -- | Go to Step 13 | -- | ||||||||||||||||
12 | Replace the ECM. Refer to Engine Control Module Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- | ||||||||||||||||
13 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 14 | ||||||||||||||||
14 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||||||||||||
