Circuit Description

A 3-Way catalytic converter is used to maintain low emissions. The PCM monitors exhaust gasses from converter using Heated Oxygen Sensor (HO2S). HO2S is located in exhaust stream past the 3-way catalytic converter. HO2S produces an output signal which indicates the oxygen capacity of the catalyst. This determines the catalyst's ability to convert exhaust emissions effectively.

During normal operation, HO2S signal will be less active than that produced by the front Oxygen Sensor (O2S). Powertrain Control Module (PCM) monitors catalyst efficiency in 2 stages. If catalyst efficiency falls to less than 75 percent, PCM will set a stage one fail flag, but will not illuminate Malfunction Indicator Light (MIL). If catalyst efficiency falls to less than 50 percent, PCM will set a stage 2 fail flag and MIL will be illuminated.

Conditions for setting this DTC are:

• Engine speed is 1700-3700 RPM.
• Coolant temperature is greater than 158°F (70°C).
• Vehicle speed is 30-80 MPH.
• No presence of Codes: P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121-P0123, P0131-P0134, P0137, P0138, P0140, P0141, P0171, P0172, P0300-P0304, P0502, P0503, P0506, P0507, P0562, P0563, P0601, P1133, P1406, P1441.
• HO2S 2 voltage varies greater than 250 mV.
• Calculated airflow is 12-29 gm/s.