For 1990-2009 cars

### Circuit Description

Heated oxygen sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature. The powertrain control module (PCM) supplies the HO2S with a reference, or bias, voltage of about 450 mV. When the engine is first started the PCM operates in open loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperature and closed loop is achieved, the HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage. High HO2S voltage indicates a rich exhaust stream; low HO2S voltage indicates a lean exhaust stream. If the PCM detects that the HO2S voltage remains within the bias voltage range, DTC P0134 sets for HO2S bank 1 sensor 1 or DTC P0154 sets for HO2S bank 2 sensor 1.

### Conditions for Running the DTC

• | DTCs P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0200, P1125, P1516 are not set.

• | The Engine Run Time parameter is more than 300 seconds.

• | The Ignition 1 Signal parameter is between 10-18 volts.

### Conditions for Setting the DTC

The PCM detects that the affected HO2S voltage parameter is between 350-550 mV for 60 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.

• | The control module commands the Loop Status open.

### 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.

### Test Description

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

1. If the voltage is varying above and below the specified value, the condition is not present.

2. With no fault present, the test lamp will blink once per second.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views
1 | Did you perform the Diagnostic System Check - Engine Controls? | -- | Go to Step 2 | Go to Diagnostic System Check - Engine Controls
2 | Important: Whenever the heated oxygen sensor (HO2S) heaters are commanded ON with a scan tool, they will continue to be pulsed ON once per second until the ignition is turned OFF for 30 seconds.

1. Turn ON the ignition, with the engine OFF.
2. Command the HO2S heaters ON with a scan tool.
3. Wait 15 seconds to allow the HO2S heater current to stabilize.
4. Observe the affected HO2S heater current parameter with a scan tool.

Is the HO2S heater current parameter within the specified range?

0.25-3.125 A

Go to Step 3

Go to Step 13

3 |

1. Start the engine.
2. Allow the engine to reach operating temperature. Refer to Scan Tool Data List .
3. Operate the engine at 1,500 RPM for 30 seconds.
4. Observe the affected HO2S voltage parameter with a scan tool.

Is the HO2S voltage parameter varying above and below the specified range?

300-600 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 Intermittent Conditions

5 |

1. Turn OFF the ignition.
2. Disconnect the affected HO2S.
3. Turn ON the ignition, with the engine OFF.
4. Observe the HO2S voltage parameter with a scan tool.

Is the HO2S voltage parameter more than the specified value?

800 mV

Go to Step 7

Go to Step 6

6 | Measure the voltage from the high signal circuit of the HO2S harness connector on the engine harness side to a good ground with the DMM. Refer to Circuit Testing in Wiring Systems. Is the voltage more than the specified value? | 0.2 V | Go to Step 8 | Go to Step 9
7 | Important: The sensor may be damaged if the circuit is shorted to a voltage source. Test the HO2S high signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 29 | Go to Step 24
8 | Measure the voltage from the low signal circuit of the HO2S harness connector on the engine harness side to a good ground with a DMM. Refer to Circuit Testing in Wiring Systems. Is the voltage more than the specified value? | 2 V | Go to Step 12 | Go to Step 10
9 | Test the HO2S high signal circuit for an open or for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 29 | Go to Step 24
10 |

1. Connect a 3-amp fused jumper wire between the high signal circuit of the HO2S harness connector on the engine harness side and the low signal circuit of the HO2S harness connector on the engine harness side.
2. Observe the HO2S voltage parameter with a scan tool.

Is the HO2S voltage parameter less than the specified value?

100 mV

Go to Step 23

Go to Step 11

11 | Test the HO2S low signal circuit for an open or for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 29 | Go to Step 24
12 | Test the HO2S low signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 29 | Go to Step 24
13 | Inspect the O2A fuse. Is the O2A fuse open? | -- | Go to Step 14 | Go to Step 15
14 |

1. Test the ignition 1 voltage circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
2. Replace the O2A fuse.

Did you find and correct the condition?

--

Go to Step 29

Go to Step 17

15 |

1. Disconnect the affected HO2S.
2. Turn ON the ignition, with the engine OFF.
3. Probe the ignition 1 voltage circuit of the HO2S harness connector on the engine harness side with a test lamp that is connected to a good ground. Refer to Probing Electrical Connectors in Wiring Systems.

Does the test lamp illuminate?

--

Go to Step 16

Go to Step 26

16 | Important: The test lamp may blink prior to commanding the heaters ON. This is because the heaters were commanded ON in a previous step. To command the heaters OFF, turn OFF the ignition for 30 seconds.

1. Connect a test lamp between the ignition 1 voltage circuit of the HO2S harness connector on the engine harness side and the HO2S heater low control circuit of the HO2S harness connector on the engine harness side.
2. Command the HO2S heaters ON with a scan tool.

Does the test lamp blink once per second?

--

Go to Step 18

Go to Step 19

17 | Important: Perform the following test on all HO2S which are supplied voltage by the suspect circuit. Test the ignition 1 voltage circuit on the sensor side of the HO2S connector for a short to ground. Refer to Circuit Testing in Wiring Systems. Is any sensor shorted to ground? | -- | Go to Step 27 | Go to Intermittent Conditions
18 | Measure the resistance of the following circuits with a DMM:

• | HO2S heater low control circuit

• | Ignition 1 voltage circuit

Refer to Circuit Testing in Wiring Systems.

Is the resistance of either circuit more than the specified value?

3 ohms

Go to Step 25

Go to Step 23

19 | Is the test lamp on steady? | -- | Go to Step 20 | Go to Step 21
20 | Test the HO2S heater low control circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 29 | Go to Step 24
21 | Test the HO2S heater low control circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 29 | Go to Step 22
22 | Test the HO2S heater low control circuit for an open or for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 29 | Go to Step 24
23 | Test for shorted terminals and for poor connections at the HO2S. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 29 | Go to Step 27
24 | Test for shorted terminals and for poor connections at the powertrain control module (PCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 29 | Go to Step 28
25 | Repair the circuit with high resistance. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 29 | --
26 | Repair the open or high resistance in the ignition 1 voltage circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 29 | --
27 | Replace the affected HO2S. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 1 or Heated Oxygen Sensor Replacement - Bank 2 Sensor 1 . Did you complete the replacement? | -- | Go to Step 29 | --
28 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 29 | --
29 |

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 30

30 | 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