Circuit Description
The heated oxygen sensors (HO2S) increase the amount of time that the sensor remains in a closed-loop fuel control or in a catalyst monitoring operation. The oxygen sensor heater greatly reduces the required amount of time for activation of the fuel control HO2S 1. The the post-catalyst HO2S 2 requires a sensor heater in order to maintain high operating temperatures. The heater helps provide accurate oxygen content readings of the engine exhaust by the HO2S.
Conditions for Running the DTC
| • | The engine has been running at idle for at least 1 minute. |
| • | The vehicle accelerates from a stop for at least 5 seconds after idling for 1 minute. |
Conditions for Setting the DTC
| • | The resistor voltage is less than 2.5 volts with the heater off. |
| • | The resistor voltage is more than 0.31 volts with the heater on. |
| • | Either of the above conditions ae present for 5 seconds. |
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) after two consecutive ignition cycles in which the diagnostic runs with the fault active. |
| • | The PCM records the operating conditions at the time that the diagnostic fails. This information is stored in the Freeze Frame buffer. |
Conditions for Clearing the DTC
| • | The MIL turns OFF after 3 consecutive trips during which the diagnostic runs and does not detect a fault. |
| • | A History DTC clears after 40 consecutive warm-up cycles without a fault. |
| • | Use the Clear DTC Information function of the scan tool, or disconnect the PCM battery feed in order to clear the DTC. |
Diagnostic Aids
Clear the DTC information. Road-test the vehicle while monitoring the HO2S Heater Test on the scan tool. When the scan tool indicates YES, check for DTC P0135 under Last Test Failed. If DTC P0135 is not indicated, the condition is intermittent, and the HO2S Heater diagnostic is indicating OK at this time.
Check for a faulty electrical connection to the PCM.
An intermittent malfunction may be caused by a fault in the electrical circuit of the HO2S 1 sensor. Inspect the wiring harness and the components for any of the following conditions:
| • | Backed out terminals |
| • | Incorrect mating of terminals |
| • | Broken electrical connector locks |
| • | Incorrectly formed terminals or damaged terminals |
| • | Faulty terminal-to-wiring connections |
| • | Physical damage to the wiring harness |
| • | A broken wire inside the insulation |
| • | Corrosion of electrical connections, of splices, or of terminals |
If DTC P0135 cannot be duplicated, the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC first set.
Test Description
The numbers below refer to the step numbers in the diagnostic table.
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The Powertrain OBD System Check prompts the technician to complete some basic checks, and to save the applicable freeze frame data on the scan tool. This creates an electronic copy of the data that was taken when the fault occurred. The scan tool saves the information for later reference.
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This step checks if the malfunction that caused the DTC P0135 is still present. Drive the vehicle under the specified conditions to verify that the fault is present. Monitor the DTC P0135 diagnostic under the MIL/System Status selection of System Information on the scan tool. The HO2S test displays a YES status in order to indicate that the purge system diagnostic is completed.If the test displays a YES, check for a DTC P0135 in the Last Test Failed screen of the scan tool. If DTC P0135 is not displayed, the HO2S system diagnostic has run and passed. This indicates that a malfunction was not present this time. The DTCs MUST be cleared in order to view the CURRENT STATUS of the system diagnostics that are being performed. Remember that the MIL/System Status test only indicates that the test has run.The test will not indicate if the test passed or failed. Check the Last Test Failed screen for related DTCs in order to determine the results of the diagnostic test that was involved.
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The HO2S 1 heater is powered by the IG-COIL fuse that is located in the junction block.
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This step measures the resistance of the heater circuit of the HO2S 1.
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This step checks for a short to ground in the HO2S 1 heater circuit. If a problem is not found in the HO2S 1 heater circuit, the problem could be a faulty HO2S 1.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | |||
Does the scan tool indicate a DTC P0135 in Last Test Failed? | -- | Go to Diagnostic Aids | ||
Is the test lamp ON? | -- | |||
4 |
Is the voltage above the specified value? | 10 V | ||
Is the HO2S 1 heater resistance within the specified value? | 11.7-14.3 ohms at 20°C (68°F) | |||
6 | Inspect the IG-COIL fuse in the fuse block. Is the fuse open? | -- | ||
7 |
Was a repair necessary? | -- | ||
Was a repair necessary? | -- | |||
9 | Repair the open in the ignition feed circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | - | |
10 | Check for a poor connection at the HO2S 1 electrical connector. Repair as necessary. Refer to Connector Repairs or Wiring Repairs to in Wiring Systems. Was a repair necessary? | -- | ||
11 | Replace the HO2S 1. Refer to Heated Oxygen Sensor Replacement . Is the action complete? | -- | - | |
12 | Replace the PCM. Is the action complete? | -- | - | |
13 |
Are any DTCs displayed on the scan tool? | -- | Go to the applicable DTC table | System OK |
