P0134

Diagnostic Chart (Part 1 Of 3):

Diagnostic Chart (Part 2 Of 3):

Diagnostic Chart (Part 3 Of 3):

Schematic:

CIRCUIT DESCRIPTION
The Heated Oxygen Sensor (HO2S) is a sensor designed to create a voltage relative to the oxygen content in the engine exhaust stream. The control module supplies the HO2S with signal high and low circuits. Ignition voltage and ground are supplied to the HO2S heater by independent circuits. The oxygen content of the exhaust indicates when the engine is operating lean or rich. When the HO2S detects that the engine is operating rich, the signal voltage is high, and decreases the signal voltage as the engine runs leaner. This oscillation above and below the bias voltage, sometimes referred to as activity or switching, can be monitored with the HO2S signal voltage.

The HO2S contains a heater that is necessary in order to quickly warm the sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. The HO2S needs to be at a high temperature in order to produce a voltage. When the HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. It also monitors the HO2S signal voltage for Closed Loop fuel control. During normal Closed Loop fuel control operation, the control module will add fuel, or enrich the mixture, when the HO2S detects a lean exhaust content. The control module will subtract fuel, or "lean-out" the mixture, when the HO2S detects a rich exhaust condition.

Certain vehicle models utilize an oxygen sensor behind the catalytic converter in order to monitor catalyst efficiency.

This Diagnostic Trouble Code (DTC) determines if the HO2S is functioning properly. It checks for an adequate number of HO2S voltage transitions above and below the bias range of 300-600 mV. This DTC sets when the Vehicle Control Module (VCM) fails to detect a minimum number of voltage transitions above and below the bias range during the test period. Possible causes of this DTC are:
^ An open or a short to voltage on either the HO2S signal or HO2S low circuits
^ A malfunctioning HO2S
^ A problem in the HO2S heater or its circuit
^ A faulty HO2S ground

This DTC determines if the HO2S is functioning properly by checking for an adequate number of HO2S voltage transitions above and below the bias range of 300-600 mV. This DTC sets when the VCM fails to detect a minimum number of voltage transitions above and below the bias range during the test period. Possible causes of this DTC are listed below.
^ An open or a short to voltage on either the HO2S signal or the HO2S low circuits
^ A malfunctioning HO2S
^ A problem in the HO2S heater or its circuit
^ A poor HO2S ground

CONDITIONS FOR RUNNING THE DTC
^ No Throttle Position (TP) sensor DTCs are active.
^ No Evaporative Emissions (EVAP) system DTCs are active.
^ No Intake Air Temperature (IAT) sensor DTCs are active.
^ No Manifold Absolute Pressure (MAP) sensor DTCs are active.
^ No Engine Coolant Temperature (ECT) sensor DTCs are active.
^ No Mass Air Flow (MAF) sensor DTCs are active.
^ No misfire DTCs are active.
^ No intrusive tests, such as an Exhaust Gas Recirculation (EGR) test or a catalyst test are in progress
^ No device control is active.
^ The system voltage is between 11.7 volts and 18 volts.
^ The engine run time is more than 120 seconds
^ The DFCO is not active.
^ The ECT is 58.5°C (137°F) or more.
^ The MAF is 13 g/s or more.
^ DTC P0135 is not active.
^ The system is in closed loop.

CONDITIONS FOR SETTING THE DTC
The O2 sensor voltage is between 300-600 mV for more than 80 seconds

ACTION TAKEN WHEN THE DTC SETS
^ The control module illuminates the Malfunction Indicator Lamp (MIL) if a failure is detected during 2 consecutive key cycles.
^ The control module sets the DTC and records the operating conditions at the time the diagnostic failed. The failure information is stored in the scan tool Freeze Frame and Failure Records.

CONDITIONS FOR CLEARING THE MIL OR DTC
^ The control module turns OFF the MIL after 3 consecutive drive trips when the test has run and passed.
^ A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle.
^ Use a scan tool in order to clear the DTCs.

DIAGNOSTIC AIDS

IMPORTANT: Never solder the HO2S wires. For proper wire and connection repairs, refer to Wiring Repairs or Connector Repairs in Diagrams.

Check for the following condition:

An exhaust leak is typically within 30.5 cm (12 in.) upstream of the HO2S. Refer to Exhaust System Inspection in Engine Exhaust. Testing and Inspection

A Malfunctioning HO2S Heater or Heater Circuit
With the ignition ON and the engine OFF, the HO2S voltage displayed on a scan tool should gradually drop to less than 0.150 volt, indicating that the heater works properly. If the voltage does not drop, disconnect the HO2S and connect a test lamp between the terminal C and terminal D. If the test lamp does not light, repair the open in the HO2S ground circuit or in the HO2S ignition positive voltage circuit. If the test lamp illuminates, replace the HO2S.

The Intermittent Test
Use a scan tool in order to monitor the HO2S signal voltage. When the engine is warm and running at part throttle in closed loop, move the related connectors and the wiring harness. If you induce a failure, the HO2S signal voltage reading changes from its normal fluctuating voltage of more than 600 mV and less than 300 mV, to a fixed value of approximately 450 mV. This procedure may help to isolate the location of the malfunction.

An intermittent may be caused by any of the following conditions:
^ A poor connection
^ Rubbed through wire insulation
^ A broken wire inside the insulation

Thoroughly inspect any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent and Poor Connections in Diagrams.

If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Diagrams.

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
2. This step checks for proper sensor activity. When in Closed Loop fuel control the HO2S voltage should rapidly swing above and below the bias voltage.
4. This step checks the VCM and the HIGH and LOW circuits between the VCM and the HO2S connector for proper operation.
7. This step checks for proper HO2S heater circuit operation up to the HO2S connector.
8. This step checks for proper circuit resistance between the HO2S LOW circuit and VCM ground.
13. This step checks for proper circuit resistance between the HO2S LOW circuit and VCM ground with a COLD sensor. A loose HO2S or poor thread to exhaust electrical contact will cause higher resistance when the HO2S is cold. Although 500 ohms is allowed, typical resistance should be less than 50 ohms.