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Forum > Smog Check Repair > Question

1993 Nissan Altima failed for high CO and HC. Please help! We're stuck.

The owner did not smog check this Nissan Altima and now we are stuck with a car that we can't register.

The vehicle produced 127 ppm HC at 15mph and 37 ppm HC at 25mph.

CO was .50% at 15mph and .09% at 25mph. NO (PPM) was also high 1236 at 15 and 86 at 25mph.

Sso as you can see everything passes at 25mph and fails at 15mph. Any idea what would cause this? Also, the vehicle seems to kind of shake while running.

Answer:

What Causes High CO? A smog check repair station will first have to find out if your 1993 Nissan Altima's fuel feedback system is working properly. We have a feeling the high CO fault is causing the high HC fault; and once air/fuel ratio is corrected and your Nissan's engine begins recieving the correct amount of fuel (during the 15 mph portion of the smog test), HC will normalize. Fuel feedback sensors such as the MAP, MAF, ECT and O2 sensors need to be diagnosed in order to ensure your Altima's emissions computer is receiving the signals from these components, the computer is computing the data properly and sending the correct signals to the fuel injectors to either increase or decrease fuel delivery to the combustion chambers. For more information on what causes high CO please follow the link below: posted by SmogTips Support

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