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. A heating element inside the HO2S minimizes the time required for the sensor to reach operating temperature. Voltage is provided to the heater by the ignition 1 voltage circuit through a fuse. With the engine running, ground is provided to the heater by the HO2S heater low control circuit, through a low side driver within the powertrain control module (PCM). The PCM monitors the current flow through the heater for diagnosis.

If the PCM detects that the HO2S heater current is outside a specified range, DTC P0135 sets for HO2S 1 or DTC P0141 sets for HO2S 2.

### Conditions for Running the DTC

• | DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0128, P0201-P0204, P0300, P0301-P0304, P0336, P0410, P0440, P0442, P0446, P0452, P0453, P0506, P0507, P0601, P0602, P1441, or P1621 are not set.

• | The ignition 1 signal parameter is between 10-17 volts.

• | The engine coolant temperature (ECT) sensor parameter is more than 70°C (158°F).

• | The fuel level sensor parameter is more than 10 percent.

• | The engine run time parameter is more than 60 seconds.

### Conditions for Setting the DTC

• | The PCM detects that the affected HO2S heater current is less than 0.217 amps or more than 1.56 amps.

• | The above condition is met for 200 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.

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 |

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

Is the HO2S heater current parameter within the specified range?

0.217-1.56 A

Go to Step 3

Go to Step 4

3 |

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 4

Go to Intermittent Conditions

4 | Inspect the EIS fuse. Is the EIS fuse open? | -- | Go to Step 5 | Go to Step 6
5 | Test the ignition 1 voltage 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 20 | Go to Step 8
6 |

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.

Does the test lamp illuminate?

--

Go to Step 7

Go to Step 17

7 |

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 heater ON and OFF with a scan tool.

Does the test lamp turn ON and OFF with each command?

--

Go to Step 9

Go to Step 10

8 | 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 the sensor shorted to ground? | -- | Go to Step 18 | Go to Intermittent Conditions
9 | 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?

3ohms

Go to Step 16

Go to Step 14

10 | Does the test lamp remain illuminated with each command? | -- | Go to Step 11 | Go to Step 12
11 | 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 20 | Go to Step 15
12 | 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 20 | Go to Step 13
13 | Test the HO2S heater low control circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 20 | Go to Step 15
14 | Test for an intermittent and for a poor connection 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 20 | Go to Step 18
15 | Test for an intermittent and for a poor connection 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 20 | Go to Step 19
16 | Repair the circuit with high resistance. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 20 | --
17 | Repair the open in the ignition 1 voltage circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 20 | --
18 | Replace the affected HO2S. Refer to Heated Oxygen Sensor 1 Replacement or Heated Oxygen Sensor 2 Replacement . Did you complete the replacement? | -- | Go to Step 20 | --
19 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 20 | --
20 | Were you sent to this diagnostic from DTC P0134? | -- | Go to Step 18 in DTC P0134 | Go to Step 21
21 | Were you sent to this diagnostic from DTC P0140? | -- | Go to Step 18 in DTC P0140 | Go to Step 22
22 |

1. Replace the EIS fuse if necessary.
2. Clear the DTCs with a scan tool.
3. Turn OFF the ignition for 30 seconds.
4. Start the engine.
5. 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 23

23 | 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