Code P0140, Oxygen Sensor No. 2 (Catalyst Monitor) Open CKT: Notes

A three-way catalytic converter is used to maintain reasonably low emissions of hydrocarbons (HC), carbon monoxide (CO) and oxides of nitrogen (NOx). The catalyst within the converter promotes a chemical reaction which oxidizes the HC and CO present in the exhaust gas, thus converting them into harmless water vapor and carbon dioxide. The catalyst also reduces NOx, converting it to nitrogen.

The PCM is capable of monitoring this process using HO2S No. 2. HO2S No. 2, which is located in the exhaust stream past the three-way catalytic converter, produces an output signal which indicates the oxygen storage capacity of the catalyst. This in turn indicates the catalyst's ability to convert exhaust emissions effectively.

HO2S No. 2 signal will be far less active than that produced by HO2S No. 1 if the catalyst is properly functioning. PCM will set Code P0140 if a problem exists which causes the PCM to detect a fixed HO2S No. 2 signal voltage between .35-.56 volt for an extended period of time. Code P0140 will set when the following conditions are present.

• Engine coolant temperature is greater than 110°F (43°C).
• Engine run time is more than 40 seconds.
• Throttle angle is greater than 3 percent.
• HO2S No. 2 signal voltage is steady between .35-.56 volt.
• Above conditions for more than 2 minutes.

Code P0140 will not illuminate Malfunction Indicator Light (MIL).