P0137

Diagnostic Chart (Part 1 Of 2):

Diagnostic Chart (Part 2 Of 2):

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 is designed to detect a HO2S voltage that remains at a low, or lean, voltage for more than 100 seconds during a 120-second test period. This DTC is set during the following conditions:
^ There is an HO2S circuit fault that results in a false lean exhaust condition.
^ The HO2S is correctly detecting the lean air-to-fuel ratio resulting from either a vacuum leak or a fuel control system fault.

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.

Lean Test Enable
^ The system is in closed loop.
^ The air-to-fuel ratio is between 14:5-14:8.
^ The throttle position is between 3.5 percent and 99 percent
^ The above conditions are met for 5 seconds

Power Enrichment Lean Test Enable
^ The system is in closed loop.
^ The power enrichment mode is active.
^ The high speed fuel cut-off is not active.
^ The elapsed time since the test enabled is more than 1 second

CONDITIONS FOR SETTING THE DTC

Lean Test
The HO2S voltage is less than 26 mV for more than 110 seconds.

Power Enrichment Lean Test
The HO2S voltage is less than 399 mV for more than 40 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 connector repair, refer to Wiring Repairs or Connector Repairs in Diagrams.

Using the scan tool, observe the long-term fuel trim (FT) values at the different RPM and air flow conditions. The scan tool also displays the fuel trim cells. You can check the long-term FT values in each of the cells in order to determine when the DTC may have set. If the conditions for this DTC exist, the long-term FT values measure approximately 158 or more.

Check for the following conditions:
^ A mispositioned sensor pigtail contacting the exhaust manifold.
^ An intermittent ground in wire between the connector and the sensor
^ A poor Vehicle Control Module (VCM) ground
^ Lean injectors-Perform the Injector Balance Test. Refer to Fuel Injector Balance Test with Tech 2. Component Tests and General Diagnostics
^ Fuel Contamination-Even small amounts of water near the in-tank fuel pump inlet can be delivered to the injectors. The water causes a lean exhaust, and can also set this DTC. Refer to Alcohol/Contaminants-In-Fuel Diagnosis. Component Tests and General Diagnostics
^ Fuel pressure-If the fuel pressure is too low, the system will be lean. In order to confirm this condition, monitor a fuel pressure gauge while you drive the vehicle at various speeds and loads. Refer to Fuel System Diagnosis. Component Tests and General Diagnostics
^ Exhaust leaks-If there is an exhaust leak, the engine may pull the outside air into the exhaust and past the sensor. Refer to Exhaust System Inspection in Engine Exhaust. Testing and Inspection
^ Vacuum or crankcase ventilation system leaks can cause a lean condition or a high idle.

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.
3. In order to determine if the engine is lean during power enrichment operate the vehicle under higher throttle/acceleration conditions while monitoring scan tool HO2S voltage and the power enrichment parameter. A lean condition will cause HO2S voltage to be less than 598 mV during power enrichment.
5. Monitor the HO2S voltage of the opposite bank sensor. If the voltage activity of the opposite bank sensor is similar to the voltage activity of the suspect sensor check for lean conditions that would affect both cylinder banks. An opposite bank sensor with normal HO2S voltage activity indicates the suspect HO2S needs replacement or a lean condition exists only on the suspect HO2S cylinder bank.