For 1990-2009 cars
Engine Controls Components
Oxygen Sensors
OBD II Symbol Description Notice
Engine Controls Connector End Views
Handling ESD Sensitive Parts Notice

### 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 catalyst's 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).

Replace the entire HO2S 2 assembly. Do not attempt to repair the HO2S 2 if the following conditions exist:

• | Damaged wiring

• | Damaged electrical connectors

• | Damaged terminals

Obstruction of the air reference and degraded HO2S 2 performance could result from any attempt to repair the above conditions.

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.

### Conditions for Setting the DTC

• | DTCs P0106, P0107, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0200, P0300, P0301, P0302, P0303, P0304, P0506, P0507, P1336, P1404, P1441 not set.

• | The engine run time is greater than 25 seconds.

• | The engine coolant temperature is greater than 40°C (104°F).

• | The Throttle Position (TP) is between 8 percent and 50 percent.

• | The air/fuel ratio is between 14.5:1 and 14.7:1.

• | The above conditions met for 140 seconds.

• | The HO2S 2 remains below 43 mV for 112 to 150 seconds.

### Action Taken When the DTC Sets

• | The malfunction indicator lamp (MIL) will illuminate after two consecutive ignition cycles in which the diagnostic runs with the malfunction present.

• | The PCM will record the operating conditions at the time that the diagnostic fails. This information will store in the Freeze Frame and Failure Records buffers.

• | A history DTC stores.

• | The coolant fan turns ON.

### Conditions for Clearing the MIL/DTC

• | The MIL will turn OFF after three consecutive ignition cycles in which the diagnostic runs without a fault.

• | A history DTC will clear after 40 consecutive warm-up cycles without a fault.

• | The MIL/DTCs can be cleared by using the scan tool.

### Diagnostic Aids

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

- | Exhaust system leaks between the three-way catalytic converter and the flange

- | Exhaust system corrosion between the three-way catalytic converter and the flange

- | Exhaust system loose or missing hardware between the three-way catalytic converter and the flange

- | Repair the conditions as necessary.

• | A poor electrical connection or a damaged harness--Inspect the harness for a short to ground in the HO2S 2 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 connections

- | A 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

• | A broken wire inside of the insulation

Replace the entire HO2S 2 assembly. Do not attempt to repair the HO2S 2 if the following conditions exist:

• | Damaged wiring

• | Damaged electrical connectors

• | Damaged terminals

Obstruction of the air reference and degraded HO2S 2 performance could result from any attempt to repair the above conditions.

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

Number(s) below refer to the step number(s) on the Diagnostic Table.

1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored on the scan tool for later reference.

2. This step determines if DTC P0137 is the result of a hard malfunction or an intermittent condition.

3. Jumping the HO2S 2 Low circuit to ground is necessary to allow the PCM to display the supplied bias voltage. If the voltage is between 0.35 and 0.55 volt, then the wiring and PCM are OK.

4. The replacement PCMs must be reprogrammed and the crankshaft position system variation procedure must be preformed. Refer to the latest Techline procedure for the PCM reprogramming and also refer to the Powertrain Control Module (PCM) for the Crankshaft variation learn procedure .

#### DTC P0137-Heated Oxygen Sensor (HO2S) Circuit Low Voltage (Sensor 2)

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 |

1. Turn the ignition ON, with the engine OFF.
2. Install a scan tool.

Is the HO2S 2 voltage less than the specified value?

200 mV (0.20V)

Go to Step 4

Go to Step 3

3 |

1. Turn the ignition switch ON, with the engine OFF.
2. Review the Freeze Frame data and note the parameters.
3. Operate the vehicle within the Freeze Frame conditions and Conditions For Setting The DTC as noted?

Is the HO2S 2 voltage less than the specified value?

40 mV (0.04V)

Go to Step 4

Go to Step 8

4 | Disconnect the HO2S 2 electrical connector and jumper the HO2S 2 sensor low circuit (PCM side) to ground. Does the scan tool indicate the HO2S 2 voltage within the specified value? | 350 mV-550 mV (0.35V-0.55V) | Go to Step 7 | Go to Step 5
5 |

1. Turn the ignition switch OFF.
2. Disconnect the PCM electrical connectors and check the HO2S 2 sensor high circuit for a short to ground or short to the HO2S 2 sensor ground circuit and repair as necessary.

Was a repair necessary?

--

Go to Step 8

Go to Step 6

6 | Replace the PCM. Is the action complete? | -- | Go to Step 8 | --
7 | Replace the HO2S 2 sensor. Is the action complete? | -- | Go to Step 8 | --
8 |

1. Using the scan tool, clear the DTCs.
2. Start the engine and idle at normal operating temperature.
3. Operate the vehicle within the Conditions for setting this DTC as specified in the supporting text.

Does the scan tool indicate that this diagnostic has ran and passed?

--

Go to Step 9

Go to Step 2

9 | Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | -- | Go to applicable DTC table | System OK