DTC P0140: Ho2S Circuit - Insufficient Activity - Sensor 2: Description

WARNING: This page is about a different car, the 2002 Oldsmobile Bravada, 2002 GMC Envoy XL, 2002 GMC Envoy, and 2002 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.

In order to control emissions, a catalytic converter converts any harmful exhaust emissions into harmless water vapor and carbon dioxide. The Powertrain Control Module (PCM) has the capability to monitor this process by using a rear Heated Oxygen Sensor 2 (HO2S 2). The HO2S 2, located in the exhaust stream past the catalytic converter, produces an output signal which indicates the storage capacity of the catalyst. This in turn indicates the catalysts ability to convert the exhaust emissions effectively. If the catalyst is functioning properly, the HO2S 2 signal will be far less active than the signal produced by the front oxygen sensor (HO2S 1). Do not attempt to repair the HO2S 2. Replace the entire HO2S 2 assembly if the following conditions exist:

Damaged wiring.
Damaged electrical connector.
Damaged terminals.

Obstruction of the air reference and degraded HO2S 2 performance could result in any attempt to repair the above conditions. The HO2S 2 must have a clean air reference in order for the HO2S 2 to function properly. This clean air reference is obtained by way of the HO2S 2 wires.