Circuit Description
The powertrain control module (PCM) supplies a bias voltage of about 450 mV between the HO2S signal and low circuits. When measured with a 10 megohm digital voltmeter, 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 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 TP sensor, EVAP system, misfire, IAT sensor, MAP sensor, fuel trim, fuel injector circuit, EGR Pintle Position, ECT sensor, CKP Sensor, or MAF sensor DTCs present. |
| • | Engine run time longer than 200 seconds. |
Conditions for Setting the DTC
HO2S 1 signal voltage remains between 400 mV and 500 mV for longer than 30 seconds.
Action Taken When the DTC Sets
| • | The PCM will illuminate the 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 and Fail Records data. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn the MIL OFF during the third consecutive trip in which the diagnostic has been 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 the scan tool Clear Info function or by disconnecting the PCM battery feed. |
Diagnostic Aids
Check for the following conditions:
| • | Poor connection or damaged harness. |
| Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness. Use a corresponding mating terminal to check for proper terminal tension. |
| • | Malfunctioning HO2S heater or heater circuit. |
| With the ignition ON, engine not running, the HO2S voltage displayed on a scan tool should gradually drop to below 250 mV or rise to above 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 light, repair the open ignition feed or sensor ground circuit as necessary. Refer to Wiring Repairs in Wiring Systems. If the test lamp lights and the HO2S signal and low circuits are OK, replace the HO2S. |
| • | Intermittent test. |
| With the ignition ON, monitor the HO2S signal voltage while moving the wiring harness and related connectors. If the malfunction is induced, the HO2S signal voltage will change. This may help isolate the location of the malfunction. |
Refer to Fail Records vehicle mileage since the diagnostic test last failed to 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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The specified value is what is measured on a correctly operating system.
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The specified value is what is measured on a correctly operating system.
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This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is replaced, the new PCM must be programmed.
Step | Action | Value(s) | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||||
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Important: If any other DTCs are set (except HO2S DTCs), perform those diagnostics first. Refer to Diagnostic Trouble Code (DTC) List/Type .
Does scan tool indicate HO2S voltage varying outside the specified values? | 400-500 mV | |||||||||
3 | Operate vehicle within Fail 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? | -- | ||||||||
Does the scan tool indicate HO2S voltage more than the specified value? | 400 mV | |||||||||
Does the voltage measure near the specified value? | 4.5V | |||||||||
Measure the voltage on the HO2S low circuit (PCM side) using a DMM that is connected to a good ground. Does the voltage measure near the specified value? | 5V | |||||||||
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 |
Important: Determine the cause of contamination before replacing the sensor. Inspect and test for the following:
Replace the effected 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 |
