For 1990-2009 cars

### Circuit Description

In order to control emissions, a catalytic converter converts any harmful exhaust emissions into harmless water vapor and carbon dioxide.

The powertrain control module (PCM) has the capability to monitor this process by using a rear heated oxygen sensor (HO2S 2). The HO2S 2 , located in the exhaust stream past the catalytic converter, produces an output signal which indicates the storage capacity of the catalyst. This in turn indicates the catalysts ability to convert the exhaust emissions effectively. If the catalyst is functioning properly, the HO2S 2 signal will be far less active than the signal produced by the front oxygen sensor (O2S 1).

### Conditions for Running the DTC

• | DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0171, P0172, P0201, P0202, P0203, P0204, P0300, P0301, P0302, P0303, P0304, P0336, P0440, P0446, P0452, P0453, P0506, P0507, P0601, P0602, or P1441 are not set.

• | The engine is in DFCO mode.

• | The battery voltage is greater than 10 volts.

• | The engine coolant temperature (ECT) is greater than 70°C (158°F).

• | The fuel level is greater than 10 percent.

• | The engine has been running more than 10 seconds.

### Conditions For Setting The DTC

The HO2S 2 remains greater than 648 mV for more than 10 seconds. The diagnostic then will run for 11 seconds after a 10-second delay in order to complete 1 test.

### 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.

### Diagnostic Aids

Check for the following conditions:

• | A rich exhaust--An overly rich exhaust may load the catalyst, causing high HO2S 2 signal voltages.

• | Silicone contamination--Silicone contamination of HO2S 2 could cause a false rich condition . A powdery white deposit on the sensor will indicate this condition.

• | A malfunctioning HO2S 2--If there is an internal short in the HO2S 2, the HO2S 2 voltage displayed on a scan tool will be more than 1 volt. Disconnect the HO2S 2 and connect a jumper wire between the HO2S 2 low signal circuit to engine ground. Replace the HO2S 2 if the displayed voltage goes from over 1000 mV to around 450 mV .

• | An intermittent test--Observe the HO2S 2 on the scan tool while moving the related electrical connectors and the wiring harness with the ignition switch turned ON. If the malfunction is induced, the HO2S 2 display will change. This should help isolate the location of the malfunction.

• | A damaged harness--Inspect PCM harness for a short to voltage in the HO2S 2 high signal circuit.

An intermittent could be the result of the following conditions:

• | A poor electrical connection

• | Rubbed through wire insulation

• | Broken wire inside the insulation

Obstruction of the air reference and degrade HO2S 2 performance could result in any attempt to repair the HO2S harness or the connector.

The HO2S 2 must have a clean air reference in order for the HO2S 2 to function properly. This clean air reference is obtained by way of the HO2S 2 wires.

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. This step determines if DTC P1138 is the result of a hard malfunction or an intermittent condition.

2. Disconnecting the HO2S 2 and connecting a jumper wire between the HO2S 2 high signal circuit and the HO2S 2 low signal circuit to ground should cause the scan tool to display HO2S 2 voltage less than 100 mV (0.1 volts). If the signal voltage is still high, the PCM is malfunctioning.

#### DTC P1138

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Engine Controls Schematics
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | Go to Diagnostic System Check - Engine Controls
2 | Are any other DTC codes set? | -- | Go to Diagnostic Trouble Code (DTC) List | Go to Step 3
3 | With the scan tool, observe the HO2S 2 voltage. Is the HO2S 2 sensor voltage more than the specified value? | 1042 mV | Go to Step 5 | Go to Step 4
4 |

1. Review the Freeze Frame data, and record the parameters.
2. Start the engine.
3. Operate the vehicle within the Freeze Frame conditions and the Conditions for Running the DTC as specified.

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

1042 mV

Go to Step 5

Go to Diagnostic Aids

5 |

1. Turn OFF the ignition.

Caution: Avoid contact with moving parts and hot surfaces while working around a running engine in order to prevent physical injury.

2. Disconnect the HO2S 2 electrical connector.
3. Disconnect the PCM connectors.
4. Connect a DMM to a ground.
5. Turn ON the ignition, with the engine OFF.
6. Probe the HO2S 2 high signal circuit.

Does the DMM indicate a voltage near the specified value?

0 V

Go to Step 6

Go to Step 7

6 |

1. Turn OFF the ignition.
2. Reconnect the PCM electrical connectors.
3. Turn ON the ignition, with the engine OFF.
4. Connect a jumper wire at the following circuits at the HO2S 2 electrical connector on the PCM side to a ground.

• | The HO2S 2 high signal circuit

• | The HO2S 2 low signal circuit

Does the scan tool indicate that the HO2S 2 sensor voltage is below the specified value?

100 mV

Go to Step 8

Go to Step 10

7 | Repair the short to voltage in the HO2S 2 high signal circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 11 | --
8 | Inspect for poor connections at the harness connector of the HO2S sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 9
9 | Caution: Avoid contact with moving parts and hot surfaces while working around a running engine in order to prevent physical injury. Replace the HO2S 2 sensor. Refer to Heated Oxygen Sensor Replacement . Did you complete the replacement? | -- | Go to Step 11 | --
10 |

1. Turn OFF the ignition.
2. Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

--

Go to Step 11

--

11 |

1. Use a scan tool in order to clear the DTCs.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

--

Go to Step 12

Go to Step 2

12 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List | System OK