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 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).

### Conditions for Running the DTC

DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0171, P0201, P0202, P0203, P0204, P0300, P0301, P0302, P0303, P0304, P0335, P0440, P0442, P0446, P0506, P0507, P0601, P0602, or P1441 are not set.

• | The ignition 1 signal is greater than 10 volts.

• | The engine coolant temperature (ECT) less than 45°C (113°F).

• | Intake air temperature (IAT) less than 45°C (113°F).

• | Difference between ECT and IAT is less than 7°C (13°F).

• | The fuel level is greater than 10 percent.

• | The rear HO2S voltage is between 395-495 mV.

### Conditions for Setting the DTC

The HO2S voltage does not go greater than 600 mV or less than 300 mV within 110-255 seconds after a cold start.

### 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

An intermittent could be the result of the following conditions:

• | Poor electrical connection

• | Moisture in the connector/wiring

• | Rubbed through wire insulation

• | Broken wire inside of the insulation

Check for a poor electrical connection or a damaged harness. Inspect the harness electrical connectors for the following conditions:

• | Improper mating

• | Broken locks

• | Improperly formed electrical connectors

• | Damaged terminals

• | A poor terminal to wire connection

• | A damaged harness

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. As the heater warms the oxygen sensor to operating temperature, the HO2S will output a voltage in relation to the amount of oxygen in the exhaust. With the ignition ON and the engine OFF, the exhaust usually contains a high oxygen content. With the engine OFF the HO2S voltage will usually decrease from the initial, or bias, voltage due to the high oxygen content.

2. This step checks for proper HO2S heater ignition 1 voltage and ground supply.

3. This step checks for proper PCM and signal circuit operation.

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 | Important: The HO2S must be cool before proceeding with a diagnosis. The ignition must remain OFF for at least one-half hour before proceeding with a diagnosis.

1. Connect the scan tool.
2. Set up the scan tool with the proper vehicle identification information prior to turning the ignition ON.
3. Turn ON the ignition, with the engine OFF.
4. As quickly as possible, observe and record the HO2S voltage for the sensor that applies to this DTC.
5. Monitor the HO2S voltage for two minutes.

Does the HO2S voltage increase or decrease from the initial voltage by at least the value specified?

150 mV

Go to Step 3

Go to Step 4

3 | The condition that set this DTC is not present. This DTC may have been set by one of the following conditions:

• | An intermittently open or high resistance HO2S high signal circuit, or a low signal circuit

• | An intermittently open or high resistance HO2S heater ignition 1 voltage, or a heater ground circuit

• | Faulty HO2S or PCM connector terminal contact

• | A defective HO2S

Repair any of the above conditions as necessary. Refer to Wiring Repairs and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Diagnostic Aids

4 |

1. Turn OFF the ignition.
2. Disconnect the HO2S connector for the sensor that applies to this DTC.
3. Connect a test lamp between the HO2S heater ignition 1 voltage circuit and ground circuit terminals at the engine harness side.
4. Turn ON the ignition, with the engine OFF.

Does the test lamp illuminate?

--

Go to Step 5

Go to Step 6

5 |

1. Disconnect the test lamp.
2. Jumper the HO2S low signal circuit terminal to a known good ground.
3. Jumper the HO2S high signal circuit terminal to a known good ground.
4. Use a scan tool, in order to monitor the HO2S voltage for the sensor that applies to this DTC.

Ensure the ignition is ON while the engine is OFF.

Is the HO2S voltage less than the specified value?

20 mV

Go to Step 8

Go to Step 7

6 | Connect the test lamp between the HO2S heater ignition 1 voltage circuit terminal at the engine harness side and a known good ground. Ensure the ignition is ON while the engine is OFF. Does the test lamp illuminate? | -- | Go to Step 10 | Go to Step 11
7 |

1. Turn OFF the ignition.
2. Remove the jumpers from the PCM connector containing the HO2S high and low signal circuits.
3. Use a DMM in order to measure the continuity of the HO2S high signal circuit and then the HO2S low signal circuit between the PCM connector terminal and the HO2S connector terminal at the engine harness side.

Does the resistance measure less than the specified value?

5 ohms

Go to Step 13

Go to Step 12

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 15 | Go to Step 9
9 | Replace the HO2S. Refer to Heated Oxygen Sensor Replacement . Did you complete the replacement? | -- | Go to Step 15 | --
10 | Repair the open HO2S heater ground circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the replacement? | -- | Go to Step 15 | --
11 | Repair the lack of voltage on the HO2S heater ignition 1 voltage circuit. Refer to Wiring Repairs in Wiring Systems. If the fuse is blown, repair the short to ground on the circuit. A blown fuse or lack of voltage to the fuse may cause other DTCs or symptoms to be present. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 15

--

12 | Repair the circuit that measured high resistance. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 15 | --
13 |

1. Check for proper PCM terminal contact.
2. Repair the connectors as necessary. Refer to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 14

14 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 15 | --
15 |

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 16

Go to Step 2

16 | 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