What can cause the Emission Inspection System (EIS) to display a 'HC hang-up' message?

• A. A sample hose leak.
• B. A faulty oxygen sensor.
• C. A misadjusted idle speed.
• D. A clogged air filter.

Answer: (A)

HC hang-up happens when the hydrocarbon reading won’t settle during the test, pointing to a problem in the sampling path rather than the engine itself. The most common cause is a leak in the sample hose. A leak lets contaminants into the sampling line—either ambient hydrocarbons or exhaust gases bypassing the proper path—so the analyzer continually sees extra hydrocarbons and the reading stays high or doesn’t drop as it should. This isn’t about the engine’s fuel mixture or air intake by itself; those issues can change overall emissions but don’t create the specific symptom of the HC reading hanging up in the sampling system. Repairing the leak and ensuring the sampling line is sealed restores normal operation.