Circuit Description
The PCM supplies a bias voltage of approximately 450 mV between the HO2S signal and the low circuits. When measured with a 10-megaohm DMM, this may display as low as 320 mV. The oxygen sensor varies the voltage from approximately 1000 mV when the exhaust is rich, to approximately 10 mV when the exhaust is lean. During closed loop operation, the PCM constantly monitors the HO2S signal and compensates for a rich or a 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 time, DTC P0134 will set.
Conditions for Running the DTC
| • | The following DTCs are not present: |
| - | TP sensor |
| - | EVAP system |
| - | Misfire |
| - | IAT sensor |
| - | MAP sensor |
| - | Fuel trim |
| - | Fuel injector circuit |
| - | EGR pintle position |
| - | ECT sensor |
| - | CKP sensor |
| - | MAF sensor |
| • | The engine run time is 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 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
Check for the following conditions:
| • | A faulty connection or damaged harness -- Inspect the harness connectors for the following conditions: |
| - | Backed-out terminals |
| - | Improper mating |
| - | Broken locks |
| - | Improperly-formed or damaged terminals |
| - | Faulty terminal-to-wire connections |
| - | Damaged harnesses |
| • | A malfunctioning HO2S heater or heater circuit -- With the ignition ON and with the engine not running, the HO2S voltage displayed on a scan tool should gradually drop to less than 250 mV or rise to more than 600 mV. If this does not occur, 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 repair the sensor ground circuit as necessary. Refer to Wiring Repairs . If the test lamp illuminates, and the HO2S signal and low circuits are OK, replace the HO2S. |
| • | An intermittent test -- With the ignition ON, monitor the HO2S signal voltage while you move the wiring harness and the related connectors. If the malfunction is induced, the HO2S signal voltage will change. This procedure may help to isolate the location of the malfunction. |
If the DTC cannot be duplicated and if the DTC is determined to be intermittent, review the Failure Records in order to determine when the DTC was last set. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
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.
-
The specified value is what is measured on a correctly-operating system.
-
When the PCM is replaced, you must program the new PCM.
Step | Action | Value(s) | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||||
|
Important: If any DTCs except HO2S DTCs, are set, refer to the other DTCs first before you proceed with this table.
Does scan tool indicate that the HO2S voltage varies outside the specified values? | 400-500 mV | |||||||||
3 | Operate vehicle within the Failure Records conditions. Does the scan tool indicate that 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 | |||||||||
Is the voltage near the specified value? | 4.5V | |||||||||
Measure the voltage on the HO2S low circuit on the PCM side, using a DMM that is connected to a good ground. Is the voltage near the specified value? | 5V | |||||||||
8 | Test the low circuit for an open or for 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 for 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 faulty 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 you replace 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 faulty 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? | -- | ||||||||
|
Important: You must program the replacement PCM. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Did you complete the replacement? | -- | -- | ||||||||
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 |
