Circuit Description

WARNING: This page is about a different car, the 2003 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.

The DTC P0136 Heated Oxygen Sensor (HO2S) 2 Circuit diagnostic monitors operation of post catalyst oxygen sensor. To control emissions of Hydrocarbons (HC), Carbon Monoxide (CO), and Oxides of Nitrogen (NOx), a three-way catalytic converter is used. The catalyst within the converter promotes a chemical reaction which oxidizes HC and CO present in exhaust gas, converting HC and CO into harmless water vapor and carbon dioxide. The catalyst also reduces NOx by converting NOx to nitrogen. Powertrain Control Module (PCM) has the ability to monitor this process using heated oxygen sensors HO2S 1 and HO2S 2. The HO2S 1 produces an output signal which indicates amount of oxygen present in exhaust gas entering the three-way catalytic converter. HO2S 2 produces an output signal which indicates oxygen storage capacity of the catalyst. This in turn indicates catalysts ability to convert exhaust gases efficiently. If catalyst is operating efficiently, HO2S 1 signal will be far more active than that produced by HO2S 2.