With Oshawa Assembly

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 and to 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 or enrich the mixture when the HO2S detects a lean exhaust content and subtract fuel, or lean-out the mixture when the HO2S detects a rich exhaust condition.

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

This Diagnostic Trouble Code (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 Powertrain Control Module (PCM) 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
^ An open HO2S low reference circuit

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

CONDITIONS FOR RUNNING THE DTC
^ No active Throttle Position (TP) sensor DTCs
^ No active Evaporative Emission (EVAP) system DTCs
^ No active Intake Air Temperature (IAT) sensor DTCs
^ No active manifold absolute pressure (MAP) sensor DTCs
^ No active Engine Coolant Temperature (ECT) sensor DTCs
^ No active Mass Air Flow (MAF) sensor DTCs
^ No active misfire DTCs
^ No intrusive test in progress
^ No device controls active
^ The system voltage is between 11.7-18 volts.

Lean Test Enable
^ The system is in Closed Loop.
^ The air/fuel ratio is between 14:5-14:8.
^ The throttle position is between 3.5-99 percent.

Power Enrichment Lean Test Enable
^ The system is in Closed Loop.
^ The power enrichment mode is active.
^ The high speed fuel cutoff is not active.
^ Time elapsed since test enable is at least 1 second.

CONDITIONS FOR SETTING THE DTC

Lean Test
The Heated Oxygen Sensor (HO2S) voltage is less than 86 mV for more than 50 seconds.

Power Enrichment Lean Test
The HO2S voltage is less than 598 mV for more than 30 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 repair, refer to Wiring Repairs in Diagrams.

Using the scan tool, observe the long term fuel trim values at the different RPM and the air flow conditions. The scan tool also displays the fuel trim cells, so the long term fuel trim values can be checked 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 fuel trim values measure around 158 or more.

Check for the following conditions:
^ A sensor pigtail may be mispositioned and contacting the exhaust system.
^ An intermittent short to ground in the signal circuit between the PCM connector and HO2S
^ A poor PCM to the engine block ground
^ Lean injectors - Perform the Injector Balance Test. Refer to Fuel Injector Balance Test with Tech 2. Component Tests and General Diagnostics
^ Fuel contamination - Water, even in small amounts, 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. Testing and Inspection
^ Fuel pressure - If the pressure is too low, the system will be lean. In order to confirm the fuel pressure, monitor the fuel pressure while driving 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 the Crankcase leaks can cause a lean condition or possibly 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 check 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, then 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 and acceleration conditions while monitoring the 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.