DTC 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 converter promotes a chemical reaction which oxidizes HC and CO present in exhaust gas, thus converting them into harmless water vapor and carbon dioxide. Catalyst also reduces NOx, converting it to nitrogen.

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

Sensor No. 2 signal will be far less active than that produced by sensor No. 1 if catalyst is properly functioning. PCM will set Code P0140 if a problem exists which causes PCM to detect a fixed sensor 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.
• Sensor No. 2 signal voltage is steady between .35-.56 volt.
• Above conditions for more than 2 minutes.