For 1990-2009 cars

### Circuit Description

Heated oxygen sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature. The powertrain control module (PCM) supplies the HO2S with a reference, or bias, voltage of about 450 mV. When the engine is first started the PCM operates in open loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperatures and Closed Loop is achieved, the HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage. High HO2S voltage indicates a rich exhaust stream. Low HO2S voltage indicates a lean exhaust stream.

If the PCM detects that the HO2S voltage remains within the bias voltage range, DTC P0140 will set.

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0140 HO2S Circuit Sufficient Activity Sensor 2

### Conditions for Running the DTC

• | DTCs P0068, P0101, P0102, P0103, P0106, P0107, P0108, P0117, P0118, P0120, P0121, P0125, P0128, P0201, P0202, P0203, P0204, P0205, P0220, P0442, P0443, P0446, P0449, P0452, P0453, P0455, P0496, P1516, P2101, P2176 are not set.

• | The ECT Sensor parameter is more than 70°C (158°F).

• | The Ignition 1 Signal parameter is between 11-18 volts.

• | The Engine Run Time parameter is more than 200 seconds.

• | The Loop Status parameter is closed.

• | DTC P0140 runs once per drive cycle when the above conditions are met.

### Conditions For Setting The DTC

• | The PCM detects that the HO2S 2 parameter is between 425-475 mV.

• | The TP Indicated Angle parameter changes more than 1 percent 3 times.

• | DTC P0140 sets within 100 seconds when the above conditions are met.

### 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.

1. An HO2S heater fault may set this DTC.

2. If the voltage is varying above and below the specified value, the condition is not present.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain 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 |

1. Start the engine.
2. Wait 15 seconds to allow the heated oxygen sensor (HO2S) 2 heater current to stabilize.
3. Observe the HO2S 2 heater current parameter with a scan tool.

Is the HO2S 2 heater current parameter within the specified range?

0.199-1.5 A

Go to Step 3

Go to DTC P0141

3 |

1. Allow the engine to reach operating temperature. Refer to Scan Tool Data List .
2. Operate the engine at 2,000 RPM for 30 seconds.
3. Quickly cycle the throttle from closed throttle to wide open throttle (WOT) 3 times, while observing the HO2S 2 voltage parameter with a scan tool.

Did the HO2S 2 change more than the specified value?

200 mV

Go to Step 4

Go to Step 5

4 |

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 5

Go to Intermittent Conditions

5 |

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

Is the HO2S 2 voltage parameter more than the specified value?

800 mV

Go to Step 6

Go to Step 7

6 | Important: The normal voltage on the high signal circuit is between 400-500 mV. Important: The sensor may be damaged if the circuit is shorted to a voltage source. Test the HO2S 2 high signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 18

Go to Step 17

7 |

1. Connect a 3-amp fused jumper wire between the high signal circuit of the HO2S 2 harness connector on the engine harness side and the low signal circuit of the HO2S 2 harness connector on the engine harness side.
2. Observe the HO2S 2 voltage parameter with a scan tool.

Is the HO2S 2 voltage parameter within the specified range?

400-500 mV

Go to Step 9

Go to Step 8

8 |

1. Remove the jumper wire from the previous step.
2. Test the HO2S 2 heater low control circuit for a short to one of the following circuits:

• | The HO2S 2 low signal circuit

• | The HO2S 2 high signal circuit

• | Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 18

Go to Step 14

9 |

1. Remove the jumper wire from the previous step.
2. Connect a 3-amp fused jumper wire from the high signal circuit of the HO2S 2 harness connector on the engine harness side and ground.
3. Observe the HO2S 2 voltage parameter with a scan tool.

Is the HO2S 2 voltage parameter within the specified range?

400-500 mV

Go to Step 11

Go to Step 10

10 |

1. Remove the jumper wire from the previous step.
2. Test the HO2S 2 low signal circuit for an open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 18

Go to Step 15

11 |

1. Remove the jumper from the previous step.
2. Measure the voltage from the high signal circuit of the HO2S 2 harness connector on the engine harness side to a good ground with a DMM. Refer to Circuit Testing .

Is the voltage more than the specified value?

1 V

Go to Step 12

Go to Step 13

12 | Important: The normal voltage on the low signal circuit is between 20-100 mV. Test the HO2S 2 low signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 18 | Go to Step 17
13 | Test the HO2S 2 high signal circuit for an open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 18 | Go to Step 15
14 | Test for an intermittent and for a poor connection at the HO2S 2. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 18 | Go to Step 16
15 | Test for an intermittent and for a poor connection at the powertrain control module (PCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 18 | Go to Step 17
16 | Notice: Refer to Heated Oxygen Sensor Resistance Learn Reset Notice in the Preface section. Replace the HO2S 2. Refer to Heated Oxygen Sensor 1 Replacement or Heated Oxygen Sensor 2 Replacement . Did you complete the replacement? | -- | Go to Step 18 | --
17 | Replace the PCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 18 | --
18 |

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 19

19 | 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