P1134

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 (PCM/VCM) supplies the HO2S with signal High and Low circuits. Ignition voltage and ground is 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 and maintain the operating temperature during extended idle conditions. The HO2S needs to be at a high temperature in order to produce a voltage. Once the HO2S has reached operating temperature, the Control Module monitors the HO2S bias, or reference, voltage as well as the HO2S signal voltage for closed loop fuel control. During normal Closed Loop fuel control operation, the Control Module will add fuel (enriches the mixture) when the HO2S detects a lean exhaust content and subtract fuel (leans-out the mixture) when the HO2S detects a rich exhaust condition.

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

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 HO2S low circuits.
^ A malfunctioning HO2S.
^ A problem in the HO2S heater or its circuit.
^ A poor HO2S ground.

This DTC determines if the difference in transition times from lean to rich or rich to lean has exceeded a maximum ratio. The VCM monitors the time it takes for the HO2S to transition from a rich (above 600 mV) to a lean (below 300 mV) and vice versa. If either of these times is longer than the other by a calibrated ratio, this DTC will set.

Conditions for Running the DTC
^ No active TP sensor DTCs
^ No active EVAP system DTCs
^ No active IAT sensor DTCs
^ No active MAP sensor DTCs
^ No active ECT sensor DTCs
^ No active MAF sensor DTCs
^ No active misfire DTCs
^ No intrusive tests (i.e., EGR or Catalyst) in progress
^ No device control in progress
^ The system voltage is between 11.7-18 volts
^ DTCs P0131, P0132, P0134, and P0135 not active
^ The system is in closed loop
^ The ECT is more than 57°C (135°F)
^ The engine has been running for more than 75 seconds
^ The MAF is between 15-55 g/s
^ The engine speed is between 1100-3000 RPM
^ EVAP canister purge active
^ The above conditions are present for more than 2 seconds

Conditions for Setting the DTC
The number of lean-to-rich and rich-to-lean transitions within a 100 second sample period were less than a calibrated number

Action Taken When the DTC Sets
The VCM turns the MIL (Malfunction Indicator Lamp) ON after 2 consecutive test failures.

The VCM records the operating conditions at the time the diagnostic fails. The Freeze Frame and Failure Records store this information.

Conditions for Clearing the MIL/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 (coolant temperature has risen 22°C (40°F) from the start-up coolant temperature and the Engine Coolant Temperature is more than 70°C (158°F) during the same ignition cycle).
^ Use the scan tool Clear Information function.

Diagnostic Aids

Important: Never solder the HO2S wires.

Inspect for the following conditions:
^ An improperly installed air intake duct
^ The air intake duct for collapsed ducting, restrictions, or a missing or plugged air filter
^ Throttle body and intake manifold vacuum leaks
^ A damaged or blocked throttle body inlet
^ Exhaust system for corrosion, leaks, or loose or missing hardware.
^ The HO2S is installed securely and the pigtail harness is not contacting the exhaust manifold or wires
^ HO2S contamination
^ The vacuum hoses for splits, kinks, and proper connections
^ Excessive water, alcohol, or other contaminants in the fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis.
^ VCM sensor grounds that are clean, tight, and properly positioned

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 check any circuitry that is suspected of causing the intermittent complaint. Refer to Intermittents and Poor Connections Diagnosis. Symptom Related Diagnostic Procedures

Test Description
The numbers below refer to the step numbers on the diagnostic table.
2. HO2S contamination is indicated if multiple Response, Switching or Time Ratio HO2S DTCs are set.
4. The use of leaded fuel may be indicated by the removal or tampering of the fuel filler restrictor.
An HO2S contaminated by silicon will have a white, powdery deposit on the portion of the HO2S that is exposed to the exhaust stream. The usual cause of silica contamination is the use of un-approved silicon RTV engine gasket material or the use of silicon based sprays or fluids within the engine.
If the cause of this contamination is not corrected, the replacement HO2S will also get contaminated.
7. Even small exhaust leaks can cause slow response from the HO2S.
12. An HO2S contaminated by silicon will have a white, powdery deposit on the portion of the HO2S that is exposed to the exhaust stream. The usual cause of silica contamination is the use of un-approved silicon RTV engine gasket material or the use of the use of silicon based sprays or fluids within the engine. If the cause of this contamination is not corrected, the replacement HO2S will also get contaminated.
13. If the voltage observed in step 8 is less than the range specified a short between the HIGH and LOW circuits or a short between the HIGH circuit and ground is indicated. With the HO2S and the VCM disconnected the resistance between the HIGH and LOW circuits and the resistance between the HIGH circuit and ground should measure infinite.
If the voltage observed in step 8 is more than the range specified a short between the HIGH circuit and an ignition voltage source is indicated.
14. If the voltage observed in step 9 is not below the voltage specified a high resistance (open) HIGH or LOW circuit is indicated.
Good circuit continuity measures less than 5 ohms with the VCM and sensor disconnected. Measure between the VCM connector and the HO2S connector. Ensure VCM terminal contact is good.