Typically high HC is caused due to improper spark delivery, but it's also very important to know if your Toyota Camry is in proper fuel control; and if its CO levels are normal. High HC means raw fuel is leaving your car's tailpipe when it should be burned in the engine. Air/fuel mixture must be 14.7 to 1 (14.7:1) in order for fuel to burn efficiently. By looking at the CO emissions which your Camry produced during the smog test we can ascertain approximately where the fault is that's causing the high HC failure. If CO emissions are high (even if not failing), it is very possible that your Camry is producing high HC due to the fuel mixture being too rich. If CO is low, then the opposite may apply; the air/fuel mixture might be too lean.
We have to recommend a hands-on diagnosis by a smog check repair station. The smog repair station will need to ensure your Toyota Camry is in proper fuel control, and that air/fuel ratio is as close to 14.7:1 as possible. During diagnosis, the smog check repair technician will check all emission components which are responsible for measuring air intake, oxygen levels in the exhaust, and fuel delivery, as well as whether your vehicle's computer (ECU) is receiving and interpreting sensor data properly. The oxygen sensor must be diagnosed for proper operation, along with two very important fuel management components; the manifold absolute pressure sensor (MAP) and the Throttle Position Sensor (TPS). The MAP sensor tells the ECU how much vacuum is in the intake manifold. Based on this data the computer can determine how much fuel to command the fuel injectors to deliver. A defective MAP sensor will absolutely cause a fuel mixture problem. The TPS tells the ECU how far you've depressed the gas pedal and how far the intake's butterfly is open. It too, if defective, will give the computer incorrect information and that will disturb air/fuel ratio.
If you plan on trying to fix your Camry's high HC problem yourself, we'd first recommend inspecting your Toyota Camry's ignition system, including the spark plugs, wires, distributor, and ignition timing; since these inspections are not complicated. Make sure the spark plug wires are affixed firmly. If everything looks ok, move on to the more complicated inspection of the fuel delivery system, i.e. oxygen sensor (s), engine coolant temperature sensor, manifold absolute pressure sensor. These components will require some auto emissions know-how and proper inspection tools. It is best left up to an experienced smog check technician.
Follow the link below for a full list of High HC Causing Problems:
What Causes High HC?
