For 1990-2009 cars
Engine Controls Components
Oxygen Sensors
OBD II Symbol Description Notice
Powertrain Control Module 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, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0171, P0200, P0300, P0301, P0302, P0303, P0304, P0341, P0404, P0506, P0507, P0601, P0602 not set.

• | Air flow is greater than 5.5 grams per second.

• | Engine Coolant Temperature (ECT) is greater than 40°C (104°F).

• | Throttle Position (TP) is between 4% and 56%.

• | HO2S 2 remains between 425 mV and 460 mV for 125 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

An intermittent could be the result of the following conditions:

• | A poor electrical connection

• | Moisture in the electrical connector/wiring

• | Rubbed-through wire insulation

• | A broken wire inside the insulation

Check for the following conditions:

• | A poor electrical connection or a damaged harness--Inspect the PCM harness for an open in the HO2S 2 signal circuit. Check for the following conditions:

- | Improper mating

- | Broken locks

- | Improperly-formed connectors

- | Damaged terminals

- | A poor terminal-to-wire connection

- | A damaged harness

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

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

• | Damaged wiring

• | Damaged electrical connector

• | Damaged terminals

Obstruction of the air reference and degraded HO2S 2 performance could result in 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

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

1. After the ignition is turned ON, the HO2S heater heats up causing the HO2S signal voltage to either increase or decrease. This indicates that the HO2S heater is OK.

2. If the HO2S voltage changes more than the specified value, the condition is not present.

3. If the voltage is below the specified value, the high signal circuit, the low signal circuit, and the PCM are OK.

4. If the voltage is above the specified value, the low signal circuit is OK.

5. Resistance below the specified value indicates the HO2S heater is shorted.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Engine Controls Schematics
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 | Important: Allow the engine to cool for one-half hour before proceeding with this diagnostic. This allows the HO2S signal voltage to return to bias voltage, approximately 447 mV.

1. Install a scan tool.
2. Turn ON the ignition, with the engine OFF.
3. Immediately observe the HO2S 2 voltage parameter with a scan tool for 2 minutes.

Does the HO2S 2 voltage change from bias voltage to more than or less than the specified range?

300-600 mV

Go to Step 3

Go to Step 5

3 |

1. Start the engine.
2. Allow the engine to reach operating temperature.
3. Operate the engine at 2,000 RPM for 30 seconds.
4. While observing the HO2S 2 voltage parameter with a scan tool, quickly cycle the throttle from closed throttle to wide open throttle, 3 times.

Did the HO2S 2 voltage change more than the specified value?

300 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 Diagnostic Aids

5 |

1. Disconnect the HO2S 2 connector.
2. Turn ON the ignition, with the engine OFF.
3. Connect a 3-amp fused jumper wire between the high signal circuit of the HO2S 2 on the engine harness side and a good ground.
4. Connect a 3-amp fused jumper wire between the low signal circuit of the HO2S 2 on the engine harness side and a good ground.
5. Observe the HO2S 2 voltage parameter with a scan tool.

Is the HO2S 2 voltage less than the specified value?

200 mV

Go to Step 9

Go to Step 6

6 |

1. Remove both jumper wires from the HO2S 2 high signal and low signal circuits.
2. Measure the voltage from the low signal circuit of the HO2S 2 on the engine harness side to a good ground with a DMM. Refer to Measuring Voltage in Wiring Systems.

Is the voltage more than the specified value?

4 V

Go to Step 7

Go to Step 8

7 | Test the HO2S 2 high signal circuit for an open. Refer to Testing for Continuity and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 21 | Go to Step 16
8 | Test the HO2S 2 low signal circuit for an open. Refer to Testing for Continuity and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 21 | Go to Step 16
9 |

1. Remove both jumper wires from the HO2S 2 high signal and low signal circuits.
2. Inspect the fuse that provides voltage to the HO2S 2 heater.

Is the fuse open?

--

Go to Step 12

Go to Step 10

10 |

1. Turn ON the ignition, with the engine OFF.
2. Probe the ignition voltage circuit of the HO2S 2 on the engine harness side with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

--

Go to Step 11

Go to Step 17

11 | Connect a test lamp between the ignition voltage circuit of the HO2S 2 on the engine harness side and the heater ground circuit of the HO2S 2 on the engine harness side. Does the test lamp illuminate? | -- | Go to Step 15 | Go to Step 18
12 |

1. Test the ignition voltage circuit of the HO2S 2 for a short to ground. Refer to Testing for Short to Ground and Wiring Repairs in Wiring Systems.
2. Replace the fuse that provides voltage to the HO2S 2 Heater.

Did you find and correct a short to ground in the ignition voltage circuit?

--

Go to Step 21

Go to Step 13

13 | Test the HO2S 2 ignition voltage circuit, sensor side, for a short to the HO2S Body. Refer to Testing for Continuity in Wiring Systems. Did you find the condition? | -- | Go to Step 19 | Go to Step 14
14 | Measure the resistance between the HO2S 2 ignition voltage circuit, sensor side, and the HO2S 2 heater ground circuit, sensor side with a DMM. Does the resistance measure below the specified value? | 3 ohms | Go to Step 19 | Go to Diagnostic Aids
15 | Inspect for poor connections at the harness connector of the HO2S 2. Refer to Intermittents and Poor Connections Diagnosis and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 21 | Go to Step 19
16 | Inspect for poor connections at the PCM. Refer to Intermittents and Poor Connections Diagnosis and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 21 | Go to Step 20
17 | Repair the open in the HO2S 2 ignition voltage circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 21 | --
18 | Repair the open in the HO2S 2 heater ground circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 21 | --
19 | Replace the HO2S 2. Refer to Heated Oxygen Sensor Replacement . Did you complete the replacement? | -- | Go to Step 21 | --
20 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 21 | --
21 |

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 22

22 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List | System OK