DTC P1438: HCAC System Variable Valve Circuit Low: 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.

The HCAC VSV is supplied with the battery voltage (12 V). When the internal transistor of the ECM turns on, the HCAC VSV opens.

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.