DTC P1081: HC Adsorber Switching Valve Bank 1 Stuck Open; DTC P1082: HC Adsorber Switching Valve Bank 1 Stuck Close; DTC P1083: HC Adsorber Switching Valve Bank 2 Stuck Open; DTC P1084: HC Adsorber Switching Valve Bank 2 Stuck Close: Description

The Hydro-Carbon Adsorber and Catalyst (HCAC) system is used to reduce the amount of HC in the exhaust emissions. In this system, the HC adsorber absorbs HC of the exhaust emissions when the catalyst is cold, and the catalyst purges the absorbed HC after the catalyst is warmed up.

When the catalyst is cold, the engine control module (ECM) turns on the HCAC VSV. The intake manifold pressure (vacuum) is applied to the HCAC actuator, and it opens the HCAC valve The exhaust emissions flow to the HC adsorber.

After the catalyst is warmed up, the ECM turns off the HCAC VSV. The HCAC valve is opened by the return spring of the HCAC actuator. The exhaust emissions flow to the catalyst

To monitor the HCAC valve operation, the ECM measures the exhaust gas temperatures (EGT) of the upstream HC adsorber and the upstream catalyst using the four EGT sensors.

When the HCAC valve is closing, the upstream exhaust gas temperature before the HC adsorber rising is large and the upstream exhaust gas temperature before the catalyst rising is small When the HCAC valve is opening, the upstream exhaust gas temperature before the HC adsorber rising is small and the upstream exhaust gas temperature before the catalyst rising is large.

Fig 1: Identifying HCAC VSV, Vacuum Hose, HCAC Actuator, HCAC Valve And Exhaust Gas Temperature Sensor

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Fig 2: Exhaust Gas Flow Diagram

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