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 engine control module (ECM). The ECM monitors the current flow through the heater for diagnosis.
If the ECM detects that the HO2S heater current is above or below a specified range, DTC P0135 sets.
Conditions for Setting the DTC
| • | DTCs P0117, P0118, and P1017 are not set. |
| • | The engine run time is greater than 30 seconds. |
| • | The filtered oxygen (O2) heater current is less than 0.1 amps. |
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will illuminate after 3 consecutive ignition cycles with a fail. |
| • | The ECM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers. |
| • | A history DTC is stored. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after 3 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. |
| • | DTCs can be cleared by using the scan tool. |
Diagnostic Aids
An intermittent may be caused by rubbed through wire insulation or a wire contacting the exhaust.
Notice: The Heated Oxygen Sensor (HO2S) and the Oxygen Sensor use a permanently attached pigtail and connector. Do not remove this pigtail from the Heated Oxygen Sensor. Damage or the removal of the pigtail or the connector could affect the proper operation of the sensor.
Take care when handling the HO2S and the O2S. Keep the in-line electrical connector and the louvered end free of grease, dirt, or other contaminants. Also avoid using cleaning solvents of any type. Do not drop the HO2S or the O2S. Do not roughly handle the HO2S or the O2S.Inspect for a poor connection or a damaged harness. Inspect harness connectors for the following conditions:
| • | Improper mating |
| • | Broken locks |
| • | Improperly formed |
| • | Damaged terminals |
| • | Poor terminal-to-wire connection |
| • | Damaged harness |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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The Diagnostic System Check - Engine Controls prompts the technician to complete some basic checks and store the Freeze Frame and Failure Records data on the scan tool, if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored on the scan tool for later reference.
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This step determines if DTC P0135 is the result of a hard failure or an intermittent condition. With the ignition ON and the engine OFF, the front heated oxygen sensor (HO2S1) voltage displayed on the scan tool should change within several minutes toward 0 or 1 volt, indicating that the heater is working properly.
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Probing terminal 2 of the HO2S1 connector verifies if voltage is available to the HO2S1 heater.
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If voltage is available at the connector, then it becomes a good voltage source to inspect for a ground at terminal 3.
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This step determines if voltage is not available at the HO2S1 due to an open in the HO2S1 fuse or an open ignition feed circuit. If the fuse is open, determine if it was due to a short in the ignition feed circuit before replacing the fuse.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Perform the Diagnostic System Check - Engine Controls. Is the check complete? | -- | Go to Step 2 | ||
Important: If the engine has just been operating, allow the engine to cool for about one-half hour before proceeding. Does the front heated oxygen sensor (HO2S1) voltage gradually change toward the specified voltage? | 0 V or 1 V | Go to Step 13 | Go to Step 3 | |
Does the test light illuminate? | -- | Go to Step 4 | Go to Step 5 | |
Connect a test light between the ignition feed and ground circuits, terminal 2 and 3 of the connector. Does the test light illuminate? | -- | Go to Step 6 | Go to Step 7 | |
Inspect the fuse in the engine fuse block. Is the fuse open? | -- | Go to Step 8 | Go to Step 9 | |
6 | Inspect the connections terminal 2 and 1 at the HO2S1 connector and repair as necessary. Is a repair necessary? | -- | Go to Step 13 | Go to Step 10 |
7 | Inspect the connections terminal 4 at the HO2S1 connector and repair as necessary. Is a repair necessary? | -- | Go to Step 13 | Go to Step 11 |
8 |
Is the action complete? | -- | Go to Step 13 | -- |
9 | Inspect the connections terminal 2 at the HO2S1 connector and repair as necessary. Is the repair complete? | -- | Go to Step 13 | Go to Step 12 |
10 | Replace the HO2S1. Refer to Heated Oxygen Sensor 1 Replacement . Is the replacement complete? | -- | Go to Step 13 | -- |
11 | Repair the open in the ignition feed circuit. Is the action complete? | -- | Go to Step 13 | -- |
12 | Repair the open in the ignition feed circuit. Is the action complete? | -- | Go to Step 13 | -- |
13 |
Does the scan tool indicate that this diagnostic has run and passed? | -- | Go to Step 14 | Go to Step 2 |
14 | Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | -- | Go to DTC List | System OK |
