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).

Obstruction of the air reference and degrade 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.

### 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 engine coolant temperature (ECT) is more than 70°C (158°F).

• | The battery voltage is greater than 10 volts.

• | The engine run time is greater than 10 seconds.

• | Throttle position (TP) angle is between 8 percent and 50 percent for 4 seconds.

• | The manifold absolute pressure (MAP) is greater than 25 kPa.

### Conditions For Setting The DTC

HO2S 2 remains below 43 mV for 150 seconds.

### 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 flange

- | Loose or missing hardware

- | 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 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:

• | 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 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. In order to determine if the engine is lean during power enrichment operate the vehicle under higher throttle/acceleration conditions while monitoring scan tool O2S voltage and the power enrichment parameter. A lean condition will cause O2S voltage to be less than 598 mV during power enrichment.

2. Monitor the O2S voltage. If the voltage activity of the O2S sensor is similar to the voltage activity of the suspect sensor, check for lean conditions that would affect both sensors.

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 |

1. Run the engine until the normal operating temperature is reached.
2. Use the scan tool, in order to monitor the HO2S voltage for the sensor that applies to this DTC.

Does the HO2S voltage measure less than the value specified?

26 mV

Go to Step 4

Go to Step 3

3 | This DTC is intermittent. Are any additional DTCs stored? | -- | Go to Diagnostic Trouble Code (DTC) List | Go to Diagnostic Aids
4 |

1. Turn OFF the ignition.
2. Disconnect the HO2S sensor.
3. Jumper the HO2S low signal circuit to a good 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 5

Go to Step 6

5 | The HO2S may be detecting a lean exhaust condition. Check for one of the following conditions:

• | HO2S connector water intrusion

• | An exhaust leak between the HO2S and the engine. Refer to Exhaust Leakage in Engine Exhaust.

• | Vacuum leaks

• | Incorrect fuel pressure. Refer to Fuel System Diagnosis .

• | Lean fuel injectors. Refer to Fuel Injector Balance Test with Tech 2 .

• | An inaccurate MAF sensor

Repair any of the above or similar engine conditions as necessary.

Did you find and correct the condition?

--

Go to Step 10

Go to Step 7

6 | Test the high signal circuit of the HO2S for a short to ground or a short to the low signal circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 9
7 | 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 8
8 | Replace the HO2S. Refer to Heated Oxygen Sensor Replacement . Did you complete the replacement? | -- | Go to Step 10 | --
9 | Replace the PCM. Refer to Powertrain Control Module 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