One of your 02 sensors is likely dead. Definitely worth replacing all 4 of the 02 sensors (with OEM/Bosch, not eBay specials that require wire splicing) if you haven't done so in the last 40K miles. I would also recommend replacing or at least cleaning the MAF while you're at it. Lots of threads on that...
Giving the ECU good sensor data will keep the fuel mixture properly set - could be your bad 02 sensor is causing the ECU to run too rich and hence the hydrocarbon levels being too high.
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