Circuit Description
The heated oxygen sensor (HO2S) produces a voltage that varies between 100 mV and 900 mV under normal operating conditions. The powertrain control module (PCM) monitors this voltage and determines if the exhaust is indicating a lean or rich fuel mixture. If the voltage input at the PCM is about 100 mV the fuel mixture is lean, and if the voltage input is about 900 mV the fuel mixture is rich. The PCM constantly monitors the HO2S signal during Closed Loop operation and compensates for a rich or a lean condition by decreasing or increasing the fuel injector pulse width as necessary. If the HO2S 1 voltage remains at or near 450 mV for an extended period of time, DTC P0134 will be set.
Conditions for Running the DTC
| • | The barometric pressure (BARO) is more than 75 kPa. |
| • | The engine coolant temperature (ECT) is between -8°C (+18°F) and +110°C (230°F). |
| • | The intake air temperature (IAT) is more than -8°C (+18°F) at engine start up. |
Conditions for Setting the DTC
| • | The HO2S 1 voltage remains less than or equal to 450 mV for 30 seconds. |
| • | The maximum HO2S 1 voltage remains less than 450 mv. |
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) after 2 consecutive ignition cycles in which the diagnostic runs with the fault active. |
| • | 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 three consecutively passing trips without a fault present. |
| • | A history DTC will clear after 40 consecutive warm-up cycles without a fault. |
| • | Perform the scan tool Clear DTC Information function in order to clear the DTC. |
Diagnostic Aids
Check for any of the following conditions:
| • | If DTCs other than fuel trim (P0171, P0172), misfire (P0300 to P0304), EGR (P0400) and HO2S 1 (P0131 to P0134) are set, diagnosis those DTCs first. |
| • | Any vacuum leaks. Check for disconnected or damaged vacuum hoses and for vacuum leaks at the intake manifold, the throttle body, the EGR system, and the crankcase ventilation system. |
| • | Any exhaust leaks. Check for exhaust leaks near the HO2S. |
| • | The fuel pressure. The system will go rich or lean if pressure is too high or too low. The PCM can compensate for minor changes. However, if the fuel pressure is too high or too low, a DTC may set. |
| • | Check the EVAP canister for fuel saturation. If the canister is full of fuel, check the canister control and the hoses. |
| • | Check for a leaking fuel pressure regulator diaphragm by checking vacuum line to regulator for the presence of fuel. |
| • | A contaminated HO2S. A contaminated oxygen sensor can fail to enter or remain in Closed Loop. Silicon contamination of the HO2S can cause a lazy HO2S voltage to be indicated. Silicone contamination is indicated by a powdery white deposit on the portion of the HO2S exposed to the exhaust stream. If contamination is found, determine the cause and correct the condition before replacing the HO2S. |
| • | A poor connection at the PCM. Inspect the harness connectors for backed out terminal, improper mating, broken locks, improperly formed or damaged terminals, and a poor terminal-to-wire connection. |
| • | A damaged wiring harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the HO2S 1 display on the scan tool while moving the connectors and the wiring harnesses related to the sensor. A change in the HO2S 1 display will indicate the location of the fault. |
| • | Follow DTC P0171 or P0172 for fuel system checks. |
If a DTC P0134 is intermittent, driving the vehicle under the following conditions can verify whether the fault is present. Perform the scan tool clear DTC information function. Road test the vehicle while monitoring the DTC P0134 diagnostic on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P0134 appears in the Not Ran Since Code Cleared list, the P0134 diagnostic has not yet run. When the DTC P0134 does not appear in the Not Ran Since Code Cleared list, the P0134 diagnostic has run. If the MIL is NOT illuminated, and there is no Pending DTC Status in DTC Information, the P0134 diagnostic has passed. The DTCs MUST be cleared in order to view the Current Status of the Not Ran Since Code Cleared list. DO NOT forget that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for Current or Pending status in order to determine the outcome of the diagnostic test involved.
An intermittent malfunction may be caused by a fault in the HO2S sensor circuit. Inspect the wiring harness and components for any of the following conditions:
| • | Any backed-out terminals |
| • | Any improper mating of terminals |
| • | Any broken electrical connector locks |
| • | Any improperly formed or damaged terminals |
| • | Any faulty terminal-to-wire connections |
| • | Any physical damage to the wiring harness |
| • | A broken wire inside the insulation |
| • | Any corrosion of the electrical connections, the splices, or the terminals |
If the DTC P0134 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.
Test Description
The numbers below refer to the step numbers in the diagnostic table.
-
The Powertrain OBD System Check 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.
-
This step determines if the fault is present. The vehicle must be at operating temperature.
-
This step checks whether the malfunction that caused the DTC P0134 is still present. Driving the vehicle under these conditions will verify whether the fault is present. After performing the scan tool clear DTC information function, the DTC P0134 diagnostic can be monitored on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If DTC P0134 appears in the Not Ran Since Code Cleared list, the P0134 diagnostic has not yet run. When DTC P0134 does not appear in the Not Ran Since Code Cleared list, the P0134 diagnostic has run. If the MIL is NOT illuminated and there is no Pending DTC Status in DTC Information, the P0134 diagnostic has passed. The DTCs MUST be cleared in order to view the Current Status of the Not Ran Since Code Cleared list. DO NOT forget that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for Current or Pending status, in order to determine the outcome of the diagnostic test involved.
-
This step checks for a voltage on the HO2S signal circuit. When the oxygen sensor is disconnected the scan tool should display 35 mV or less.
-
This step checks for an open in the HO2S 1 ground circuit.
-
This step checks the HO2S 1 signal circuit. The DMM is used as a low Current voltage source, taking the place of the HO2S. This test verifies whether the signal wire is good, and whether the PCM is able to receive and process a signal from the HO2S.
-
A possible cause of a voltage short to the HO2S signal circuit is water. Check the wiring harness and PCM connectors for water that may cause ignition positive voltage to be shorted to the signal circuit.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | |||
2 | Are any DTCs set other than DTCs P0131, P0132, P0133, P0136, P0171, or P0172? | -- | ||
Does the HO2S 1 voltage switch below and above the specified value? | 300 mV - 600 mV | |||
Does the HO2S 1 voltage switch below and above the specified value? | 300 mV - 600 mV | Go to Diagnostic Aids | ||
Is the HO2S 1 voltage within the specified range? | 0 mV - 35 mV | |||
Probe the harness side of the HO2S 1 ground circuit with a test lamp connected to B+. Does the test lamp illuminate? | -- | |||
Does the scan tool indicate a HO2S 1 voltage at the specified value? | 1275 mV | |||
8 |
Was a repair necessary? | -- | ||
9 |
Was a repair necessary? | -- | ||
Was a repair necessary? | -- | |||
11 | Replace the HO2S 1. Refer to Heated Oxygen Sensor Replacement . Is the action complete? | -- | -- | |
12 |
Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | |
13 |
Are any DTCs displayed on the scan tool? | -- | System OK |
