Most common questions used to investigate
Did your car's report say "HC"?
Does the report say "CO"?
Does the report say both "HC" and "CO"?
Does the report say "NOx"?
Common conclusions
This means that there are excessive hydrocarbons in the exhaust. This is usually due to unburned gas passing through the engine and out the exhaust. This often happens when the engine misfires. Engine misfires could be caused by many different things, like misaligned timing belt, or faulty sparkplugs.
This means that there's too much carbon monoxide in your exhaust, which usually means that the engine is running rich. This means that there's too much fuel in the air-fuel mixture that is burned in the engine. This is usually a problem with the EFI system.
If both hydrocarbons and carbon monoxides are too high, the problem usually lies outside of the engine, most probably in the catalytic converter, which might need replacing.
This means there's excessive amounts of nitrogen oxide in the exhaust, which means that the exhaust gas recirculation system of your car might be malfunctioning. You need to have this checked out immediately as it could cause serious damage to your engine.
References
Related Problems
