Circuit Description
The powertrain control module (PCM) supplies a bias voltage of about 450 mV between the heated oxygen sensor (HO2S) signal and low circuits. When measured with a 10 megaohm DMM, this may display as low as 320 mV. The oxygen sensor varies the voltage within a range of about 1000 mV when the exhaust is rich, down through about 10 mV when exhaust is lean. The PCM constantly monitors the HO2S signal during Closed Loop operation and compensates for a rich or lean condition by decreasing or increasing the injector pulse width as necessary. If the HO2S 1 voltage remains at or near the 450 mV bias for an extended period of time, DTC P0134 will be set, indicating an open sensor signal or sensor low circuit.
Conditions for Running the DTC
| • | No active TP, MAP, MAF, ECT, IAT, CKP, misfire, fuel injector circuit, EVAP, or EGR DTCs are present. |
| • | The system voltage is between 9.0 volts and 18.0 volts. |
| • | The engine run time is more than 200 seconds. |
| • | The ECT is more than 75°C (167°F). |
Conditions for Setting the DTC
The HO2S 1 signal voltage remains between 400 mV and 500 mV for more than 29 seconds
Action Taken When the DTC Sets
| • | The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed. |
| • | The PCM will store conditions which were present when the DTC set as Freeze Frame/Failure Records data. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has run and passed. |
| • | The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC can be cleared by using a scan tool. |
Diagnostic Aids
Inspect for the following conditions:
| • | A poor connection or a damaged harness. Inspect the harness connectors for the following conditions: |
| • | Backed-out terminals |
| • | Improper mating |
| • | Broken locks |
| • | Improperly formed or damaged terminals |
| • | Poor terminal-to-wire connections |
| • | A damaged harness |
| • | Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. |
| • | A faulty HO2S heater or heater circuit. With the ignition ON and the engine OFF, the HO2S voltage displayed on a scan tool should gradually drop to less than 250 mV or rise to more than 600 mV. If not, disconnect the HO2S and connect a test lamp between the HO2S ignition feed and heater ground circuits. If the test lamp does not illuminate, repair the open ignition feed or the sensor ground circuit as necessary. Refer to Wiring Repairs in Wiring Systems. . If the test lamp illuminates and the HO2S signal and low circuits are OK, replace the HO2S. Refer to Wiring Repairs in Wiring Systems. |
| • | Perform an intermittent test. With the ignition ON, monitor the HO2S signal voltage while moving the wiring harness and the related connectors. If the fault is induced, the HO2S signal voltage will change. This may help isolate the location of the malfunction. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. |
Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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When the system is operating correctly the HO2S voltage should toggle above and below the specified values.
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If the low circuit is shorted to ground the HO2S voltage will be less than 400 mV when the signal circuit is jumped to ground.
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This vehicle is equipped with a PCM which utilizes an electrically erasable programmable read only memory (EEPROM). If the PCM is replaced, the new PCM must be programmed.
Step | Action | Values | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||||
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Important: If any DTCs other than HO2S DTCs are set , refer to the other DTCs first before proceeding with this table.
Does the HO2S voltage vary outside the specified range? | 400-500 mV | |||||||||
3 | Operate the vehicle within the Failure Records conditions. Does the scan tool indicate this DTC failed this ignition? | -- | Go to Diagnostic Aids | |||||||
4 | Inspect and test for the following:
Did you find and correct the condition? | -- | ||||||||
Is the HO2S voltage more than the specified value? | 400 mV | |||||||||
6 |
Does the voltage measure near the specified value? | 4.5 V | ||||||||
7 | Measure the voltage on the PCM side of the HO2S low circuit using a DMM connected to ground. Does the voltage measure near the specified value? | 5 V | ||||||||
8 | Test the low circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||||||||
9 | Test the signal circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||||||||
10 | Test the low circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||||||||
11 | Test 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? | -- | ||||||||
12 |
Notice: Contamination of the oxygen sensor can result from the use of an inappropriate RTV sealant (not oxygen sensor safe) or excessive engine coolant or oil consumption. Remove the HO2S and visually inspect the portion of the sensor exposed to the exhaust stream in order to check for contamination. If contaminated, the portion of the sensor exposed to the exhaust stream will have a white powdery coating. Silicon contamination causes a high but false HO2S signal voltage (rich exhaust indication). The control module will then reduce the amount of fuel delivered to the engine, causing a severe driveability problem. Eliminate the source of contamination before replacing the oxygen sensor. Important: Determine the cause of contamination before replacing the sensor. Inspect and test for the following:
Replace the affected HO2S sensor. Refer to Heated Oxygen Sensor Replacement . Did you complete the repair? | -- | -- | |||||||
13 | Test for poor connections at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||||||||
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Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Did you complete the repair? | -- | -- | ||||||||
15 |
Does the DTC reset? | -- | ||||||||
16 | Use the scan tool in order to check for DTCs. Does the scan tool indicate any DTCs that you have not diagnosed? | -- | Go to the applicable DTC table | System OK |
