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.
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