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 power enrichment mode.

• | The battery voltage is greater than 10.0 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 less than 400 mV for more than 5 seconds. The diagnostic then will run for 11 seconds after a 5-second delay.

### 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

• | The exhaust system--Inspect the exhaust system for the following conditions:

- | Leaks

- | Corrosion between the 3-way catalytic converter and the flang

- | Loose or missing hardware

- | Repair as necessary.

• | A poor electrical connection or a damaged harness--Inspect the harness for a short to ground in the HO2S 2 high signal circuit. Ensure that the HO2S 2 pigtail is not contacting the exhaust.

| Check for the following conditions:

- | Wiring contacting the exhaust system

- | Improper mating

- | Broken locks

- | Improperly formed harness connectors

- | Damaged terminals

- | Poor terminal to wire connection

- | Damaged harness

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

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 degraded HO2S 2 performance could result in any attempt to repair the HO2S harness or 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 P1137 is the result of a hard malfunction or an intermittent condition.

2. You may need to jump the HO2S 2 low signal circuit to ground in order to allow the PCM to display the supplied bias voltage. The PCM and the wiring are OK if the voltage is between 0.35-0.55 volt .

#### DTC P1137- HO2S Circuit Low Voltage During Power Enrichment Sensor 2

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 DTCs codes set? | -- | Go to Diagnostic Trouble Code (DTC) List | Go to Step 3
3 |

1. Turn ON the ignition, with the engine OFF.
2. With the scan tool observe the HO2S 2 voltage.

Does the HO2S 2 voltage read less than the specified value?

22 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.

Does the HO2S 2 voltage measure less than the specified value?

40 mV

Go to Step 5

Go to Step 10

5 |

1. Turn OFF the ignition.
2. Disconnect the HO2S sensor.
3. Jumper the HO2S low signal circuit to a ground.
4. Turn ON the ignition, with the engine OFF.
5. Measure the voltage on the HO2S high signal circuit on the PCM side, using a DMM that is connected to a good ground.

Does the voltage measure within the specified value?

351-551 mV

Go to Step 8

Go to Step 6

6 |

1. Turn OFF the ignition.
2. Disconnect the PCM electrical connectors.
3. Test the HO2S 2 sensor high signal circuit for the following conditions:

• | A short to ground

• | A short to the HO2S 2 sensor ground circuit

4. If you find a problem, repair the condition as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 10

Go to Step 7

7 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 10 | --
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 10 | Go to Step 9
9 |

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. Replace the HO2S 2 sensor. Refer to Heated Oxygen Sensor Replacement .

Did you complete the replacement?

--

Go to Step 10

--

10 |

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 11

Go to Step 2

11 | 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