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 |
If the ECM detects that the HO2S voltage does not increase after exiting decel fuel cut-off (DFCO) mode, this DTC sets.
DTC Descriptor
This diagnostic procedure supports the following DTCs:
DTC P0140 HO2S Insufficient Activity Sensor 2
Conditions for Running the DTC
| • | DTCs P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0137, P0138, P0300, P0335, P0336, P0337, P0341, P0400, P0404, P0405, P0406, P1320, and P1321 are not set. |
| • | The engine is operating. |
| • | The engine speed is between 2,400-3,000 RPM. |
| • | The ignition 1 voltage is more than 10 volts. |
| • | The fuel system is in closed loop. |
| • | The engine coolant temperature (ECT) is more than 70°C (158°F). |
| • | The vehicle speed is between 26-54 km/h (16.2-33.6 mph). |
| • | The manifold air pressure (MAP) is more than 70 kPa (10.1 psi). |
| • | The DTC runs continuously once the above conditions are met. |
Conditions for Setting the DTC
The ECM detects that the HO2S voltage does not transition from rich to lean or lean to rich during 7.8 seconds.
Action Taken when the DTC Sets
| • | The malfunction indicator lamp (MIL) will illuminate. |
| • | The ECM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers. |
| • | The coolant fan turns ON. |
| • | The vehicle will operate in open loop. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after 4 consecutive ignition cycles in which the diagnostic runs without a fault. |
| • | DTCs can be cleared by using the scan tool. |
| • | Disconnect the ECM battery feed for 10 seconds. |
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 other DTCs are set, refer to those DTCs before proceeding with this diagnostic table.
Did the DTC 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 2 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 2 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 HO2S. After you inspect the exhaust system, return to this diagnostic. 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 HO2S. Refer to Heated Oxygen Sensor 2 Replacement . 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 | Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||||||||||||
