Circuit Description
The DTC P0134 Heated Oxygen Sensor (HO2S) Circuit Sensor 1 diagnostic detects an inactive or fixed HO2S signal. The heated oxygen sensor (HO2S) produces a voltage that varies between 100-900 mV. The powertrain control module (PCM) monitors this voltage and determines by the exhaust gas oxygen content whether the air/fuel mixture is rich or lean. When the voltage input at the PCM is about 100 mV, the HO2S is indicating a lean air/fuel mixture. When the voltage input is about 900 mV, the HO2S is indicating rich air/fuel mixture. The PCM constantly monitors the HO2S signal during Closed Loop operation and compensates for the rich or the lean condition by decreasing or increasing fuel injector pulse width. A DTC P0134 may set if the HO2S 1 voltage remains excessively high or low for an extended period of time.
Air Fuel Mixture | Exhaust O2 Content | HO2S 1 Output | Fuel System Response |
|---|---|---|---|
Lean Mixture | High Oxygen | Low Voltage | Rich Command |
Rich Mixture | Low Oxygen | High Voltage | Lean Command |
Conditions for Running the DTC
| • | The engine coolant temperature (ECT) is more than 40°C (107°F). |
| • | The engine has been running for at least 180 seconds and is in CLOSED LOOP. |
| • | Engine speed is at least 1,400 RPM. |
| • | The vehicle speed is between 40-80 km/h (25-81 mph). |
| • | DTC P0134 runs once per drive cycle when the above conditions have been met. |
Conditions for Setting the DTC
| • | The HO2S 1 output voltage is always less than 45 mV. |
| • | The above condition is present for at least 65 seconds. |
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL). |
| • | The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer. |
Conditions for Clearing the MIL/DTC
| • | The MIL turns OFF after 3 consecutively passing trips without a fault present. |
| • | A History DTC clears after 40 consecutive warm-up cycles without a fault. |
| • | Use the scan tool Clear DTC Information function in order to clear the DTC. |
Diagnostic Aids
| • | A DTC P0134 can set when the vehicle runs out of fuel. Ask the vehicle operator if the vehicle has recently been run out of fuel. |
| • | The scan tool output control feature, Fuel Injector Modification, can be used at idle to check the oxygen sensor performance. Increasing the Fuel Injector Modification Commanded State to 25 percent should cause the HO2S 1 voltage to exceed 800 mV. Decreasing the Fuel Injector Modification Commanded State to -12 percent should cause the HO2S 1 voltage to drop to less than 100 mV. An oxygen sensor that fails to respond accordingly may be faulty or contaminated. When performing a Fuel Injector Modification with the scan tool, the Loop Status will remain Open Loop and the Short Term FT will be fixed at 0 percent. |
| • | If a DTC P0134 is intermittent, driving the vehicle under the conditions outlined in the Inspection/Maintenance (I/M) section can verify whether the fault is present. Refer to Inspection/Maintenance Heated Oxygen Sensor/Oxygen Sensor System Set . |
| • | Check for any of the following conditions: |
| - | A misrouted heated oxygen sensor wiring--The sensor pigtail may be misrouted and contacting the exhaust system causing a short to ground. |
| - | Verify the PCM to engine electrical grounds are OK. |
| - | An incorrect fuel pressure--The fuel system can go lean if the fuel pressure is too low and DTC P0134 may be set. Refer to Fuel System Diagnosis . |
| - | An incorrectly calibrated fuel injector. |
| - | Any vacuum leaks--inspect for disconnected or damaged vacuum hoses and for vacuum leaks at the intake manifold, the throttle body, and the crankcase ventilation system. |
| - | Any exhaust leaks near the HO2S. An exhaust leak may cause outside air to be pulled into the exhaust gas stream and past the HO2S. The outside air may cause DTC P0134 to set. |
| - | A shorted HO2S--An HO2S that is shorted to ground will display less than 0.1 volt on the scan tool. An HO2S that is shorted to voltage will display a reading of more than 1.0 volt on the scan tool. Water contamination of the HO2S can cause a low or high HO2S voltage to be indicated. A DTC P0134 that occurs more frequently when driving through standing water or when operating the vehicle in wet driving conditions can indicate water intrusion. Replace the HO2S if the sensor is adversely affected by moisture. |
| - | A contaminated HO2S--Silicon contamination of the HO2S can cause a low signal voltage to be indicated. Silicon contamination is indicated by a powdery white deposit on the portion of the HO2S exposed to the exhaust stream. Before replacing the HO2S, determine the cause of the contamination and correct the condition. |
| - | Fuel contamination--Small amounts of water can be delivered to the fuel injectors and cause a lean exhaust indication. A lean exhaust indication can also be caused by too much alcohol in the fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis . |
| - | A faulty electrical connection to the PCM |
| • | An intermittent malfunction may be caused by a fault in the HO2S 1 electrical circuit. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions . |
| • | Repair any electrical circuit faults that were found. Refer to Wiring Repairs in Wiring Systems. |
| • | The information included in 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 on the diagnostic table.
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The Diagnostic System Check-Engine Controls prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
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This step verifies whether the malfunction is presently occurring.
-
This step checks whether the malfunction that caused the DTC P0134 is still present. Operating the vehicle in Check Mode enhances the diagnostic capabilities of the PCM. The HO2S 1 diagnostic can be monitored on the scan tool under the I/M System Information selection. When the HO2S test displays a YES status, indicating that the heated oxygen sensor system diagnostic is completed, check for DTC P0134 in the Last Test Failed screen of the scan tool. If there is no DTC P0134 displayed, the HO2S diagnostic has run and passed, indicating that no malfunction was present this time. The DTCs MUST be cleared in order to view the Current Status of the system diagnostics being performed. Do not forget that the I/M System Information tests only indicate that the test has run, not whether the test passed or failed. The Last Test Failed screen must be checked for related DTCs in order to determine the outcome of the diagnostic test involved.
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In this step the DMM is used as a low current voltage source taking the place of the HO2S. This step verifies whether the PCM is able to receive and process a signal from the HO2S 1.
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A condition that affects the fuel mixture or combustion event in the engine can impact the operation of the HO2S. This can cause an accurate signal from the HO2S to fail the diagnostic. Performing the tests listed in Diagnostic Aids will eliminate a faulty running condition and prevent the replacement of a good oxygen sensor.
Step | Action | Values | Yes | No | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views | ||||||||||||||||
Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | ||||||||||||||
2 | Are any DTCs set other than DTC P0134? | -- | Go to Step 3 | |||||||||||||
Does the HO2S 1 voltage vary within the specified range? | 200-900 mV | Go to Step 4 | Go to Step 5 | |||||||||||||
Did DTC P0134 set? | -- | Go to Step 5 | Go to Diagnostic Aids | |||||||||||||
Is the voltage more than the specified value? | 1,155 mV | Go to Step 6 | Go to Step 7 | |||||||||||||
6 |
Does the test lamp illuminate? | -- | Go to Step 9 | Go to Step 8 | ||||||||||||
7 |
Did you find and repair a condition? | -- | Go to Step 12 | Go to Step 11 | ||||||||||||
8 | Repair the open in the HO2S 1 ground circuit between the HO2S 1 and G104. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 12 | -- | ||||||||||||
Did you find and repair a condition? | -- | Go to Step 12 | Go to Step 10 | |||||||||||||
10 | Replace the HO2S 1. Refer to Heated Oxygen Sensor 1 Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- | ||||||||||||
11 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement | -- | Go to Step 12 | -- | ||||||||||||
12 |
Did the DTC run and pass? | -- | Go to Step 13 | Go to Step 2 | ||||||||||||
13 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||||||||||
