Matching You with a Pre-Screened Smog Check Center You will Love
Free Online Smog Check Diagnosis
$500 Free Consumer Repair Assistance
Failed Emissions Test
How to Pass the Test
Who Else Wants To Pass the Smog Check
Which Type Should I Choose?
    Forum > Failed Smog Test > Question

Join the community and post your questions. Ask-A-Tech right now!

Failed Smog Test

1997 Geo Prizm Failed for High HC

My Geo Prizm failed the HC (PPM) part of the smog check. It was 119 at 15mph and 47 at 25mph. The maximum could only be 64 and 47. Why would it be so high? O2 sensor, catalytic converter? I just did an oil change and new spark plugs. Thanks.


There could be a multitude of reasons which would cause your Geo Prizm to produce and fail the smog check for high HC. It's important to know how much CO your Goe Prizm produced as well in order to know better what the cause of the high HC is.

HC (Hydrocarbon) is basically raw fuel. If your Geo failed for high HC but was producing normal CO we would suspect the vehicle's ignition system (spark). HC emissions have a direct correlation to CO. The amount of HC left over after the combustion process is based on the amount of fuel having actually entered the combustion chambers. A "rich" or "lean" fuel mixture would contribute to high HC. Air/Fuel ratio must be at an optimum 14.7:1 in order to fuel to burn efficiently.

We recommend first inspecting your Geo Prizm's ignition system first. Since you have already replaced the spark plugs, inspect the spark plug wires, distributor and coil. If everything looks ok, move on to the inspection of the fuel delivery system, i.e. the oxygen sensor (s), engine coolant temperature sensor, manifold absolute pressure (MAP) sensor. The MAP sensor is vital to proper air/fuel ratio. Your vehicle's ECU relies heavily on the MAP sensor input to determine the amount of fuel to deliver the combustion chambers. NOTE: Inspecting these components will require some auto emissions know-how and proper inspection tools. If you are capable, a repair manual will help.

The link below will give you a full list of problems which could cause high HC smog check failures.

What Causes High HC?

posted by SmogTips Support 10-15-2014 05:18 PM
Get Your DMV Registration Sticker Quicker!
Covid 19 Impact - Option for DMV service without delay.
NeedTags - OL #89953. California authorized online vehicle registration service provider.

Related questions and answers you might find useful:

Chevy k10 1984 with a 1990 crate engine from out of state by Jonny on 06-20-2021 10:36 AM

1976 Jeep CJ7 with 304 V8 & AT components by Derek on 06-18-2021 03:59 PM

My question is in regards to something my neighbor told about having my 2004 GMC Sierra SLT Smog Checked! by Richard on 06-18-2021 01:46 PM

Jeep Wrangler Sport DMV Registration Is Due In 7 Days by Irack on 10-02-2020 04:18 PM

Do I Have to Smog a Vehicle I Want to Make a Non Op? by Natali on 03-28-2020 09:05 AM