My'92 Toyota P'up runs great, has had thorough annual maintenance since purchased new, & odometer is now at 166,500 miles. My last smog check indicated that the M1: 15 MPH "HC" (PPM) MEAS was 95, which is the MAX limit, per the inspection report. (All other test result variables were well within normal, passing ranges.) The smog tech. told me that, due to the subject "HC" level, it would not pass my next smog test, and offered no corrective suggestions.

So, I have been advised (variously) to install an new Catalytic Convertor, add Seafoam Motor Treatment to the gas tank, get a tune-up a week before test, etc. I would appreciate any & all educated opinions in my effort to get the "HC" MEAS. down to passing levels, if that's at all possible. Thanks!!

1 Answer 1


HC stands for hydrocarbons, meaning there's high levels of unburnt hydrocarbons in your exhaust. It could be a cylinder isn't firing right, worn plugs, your fuel-air mixture could be wrong, a sensor could be reporting improperly or just broken, lots of things, none of which are that big a deal.

Get your OBD codes read to see what is in there, it may be a big clue. Get a tune up, but do it now - incomplete combustion can lead to other problems and it means your engine isn't running efficiently, it's your money coming out of the exhaust pipe!

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .