Circuit Description
The powertrain control module (PCM) supplies a bias voltage of about 450 mV between the heated oxygen sensor (HO2S) high signal and low signal 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 the 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 time, DTC P0134 will be set, indicating an open HO2S high signal or HO2S low signal circuit.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0201, P0202, P0203, P0204, P0205, P0206, P0410, P0440, P0442, P0443, P0446, P0449, or P1441 are not set. |
| • | The engine run time is longer than 200 seconds. |
Conditions for Setting the DTC
The heated oxygen sensor (HO2S 1) signal voltage remains between 400-500 mV for more 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. |
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. |
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 H02S high or low signal 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.
Step | Action | Values | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||
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Important: If any other DTCs are set except the HO2S DTCs, perform those diagnostics first. Refer to Diagnostic Trouble Code (DTC) List .
Does scan tool indicate that the HO2S voltage varies outside the specified values? | 400-500 mV | Go to Step 3 | Go to Step 4 | |||||||
3 | Operate vehicle within Failure Records conditions. Does the scan tool indicate this DTC failed this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids | ||||||
4 | Inspect and test for the following conditions:
Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 5 | ||||||
Does the scan tool indicate HO2S voltage more than the specified value? | 400 mV | Go to Step 6 | Go to Step 10 | |||||||
Does the voltage measure near the specified value? | 4.5 V | Go to Step 7 | Go to Step 9 | |||||||
Measure the voltage on the HO2S low signal circuit on the PCM side, using a DMM that is connected to a good ground. Does the voltage measure near the specified value? | 5 V | Go to Step 11 | Go to Step 8 | |||||||
8 | Test the H02S low 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? | -- | Go to Step 15 | Go to Step 13 | ||||||
9 | Test the H02S high 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? | -- | Go to Step 15 | Go to Step 13 | ||||||
10 | Test the H02S low signal circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 14 | ||||||
11 | Inspect for poor connections at the harness connector of the H02S sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 12 | ||||||
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.
Did you complete the replacement? | -- | Go to Step 15 | -- | ||||||
13 | Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 14 | ||||||
14 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 15 | -- | ||||||
15 |
Does the DTC run and pass? | -- | Go to Step 16 | Go to Step 2 | ||||||
16 | With a scan tool observe the stored information in Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||||
