Bank 1 Sensor 3

Circuit Description
This diagnostic test is designed in order to measure the efficiency of the Three-way Catalytic Converter (TWC) system. Catalytic convertor efficiency is a measure of its ability to store oxygen after converting the levels of hydrocarbon (HC), carbon monoxide (CO), and oxides of nitrogen (NOx) to less harmful gases. The Control Module (PCM/VCM) is able to evaluate the catalyst efficiency once the vehicle has met the enable criteria and the vehicle is at idle instead of steady cruise speeds as in the past. Once the conditions for running this DTC are met, the Control Module commands either a lean or rich air/fuel ratio depending on the current state of the exhaust oxygen level. The Control Module issues a rich command if the exhaust is currently lean, or a lean command if the exhaust is currently rich. After completion of the first command, a second and opposite command is issued.

For example, if the Control Module were to command a rich mixture, the upstream HO2S voltage would increase immediately. The rich mixture is delayed in reaching the downstream HO2S due to the conversion process occurring within the converter. The higher the efficiency, the more the delay before the rich or lean mixture is detected by the downstream O2 sensor. As a result of the lower conversion efficiency within a damaged or poisoned catalyst, the delay in the rich or lean mixture reaching the downstream O2 sensor is significantly shorter. This DTC monitors the amount of time required for both the upstream and downstream HO2S voltages to cross a calibrated voltage threshold in response to the rich or lean command.

Conditions for Running the DTC
^ No active secondary AIR DTCs
^ No active CMP sensor DTCs
^ No active ECT sensor DTCs
^ No active EGR DTCs
^ No active fuel trim DTCs
^ No active IAC DTCs
^ No active IAT sensor DTCs
^ No active MAF sensor DTCs
^ No active MAP sensor DTCs
^ No active O2 sensor DTCs
^ No active transmission DTCs
^ No active EVAP system DTCs
^ No active TP sensor DTCs
^ No active VS sensor DTCs
^ No active misfire DTCs
^ The engine speed is 1100 RPM or more for more than 44 seconds since last idle period
^ The engine has been running for at least 360 seconds and the long term fuel trim is stable
^ The predicted catalyst temperature is more than 390°C (887°F)
^ The system is in closed loop
^ The BARO is 73 kPa or more
^ The IAT is more than -7-117°C (20°-167°F)
^ The ECT is between 75-117°C (167-243°F)
^ The engine has been idling for less than 120 seconds
^ The actual engine speed is within 100 RPM of the desired idle speed

Conditions for Setting the DTC
The VCM determines that the oxygen storage capacity of the catalyst has degraded below a calibrated threshold

Action Taken When the DTC Sets
^ The Control Module illuminates the Malfunction Indicator Lamp (MIL) the first time the diagnostic runs and fails.
^ The Control Module will set the DTC and records the operating conditions at the time the diagnostic fails. The Control Module stores the failure information in the scan tools Freeze Frame and/or the Failure Records.

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
The use of fuel with a high sulfur or lead content can degrade a marginal converter's performance. Be sure to test fuel quality.

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.

Test Description
The numbers below refer to the step numbers in the diagnostic table.
3. This table checks for conditions that can cause the Three-way Catalytic Converter efficiency to appear degraded. Inspect and repair exhaust system as necessary.
6. Before the Three-way Catalytic Converter is replaced, make sure that the following conditions are not present:
^ Misfire
^ High engine oil consumption or coolant consumption
^ Retarded spark timing or weak spark