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My 2000 Toyota 4Runner failed the smog test because of high NO, everything else passed.

2000 Toyota 4Runner, V6. It passed everything but NO "PPM". MEAS was 940, 837 MAX 508, 761. What caused my Toyota to produce high NO?
Answer:

High NO on your Toyota SUV can be caused either due to a lean fuel condition (this is when the engine is not getting enough fuel to cool the combustion chamber down), or due to a bad or defective catalytic converter. Your 2000 Toyota 4Runner should be equipped with a Non-EGR equipped 3.4 liter engine. Once all other emissions components are inspected, and either fixed or found to be functioning properly, you may suspect a damaged CAT (Catalytic Converter). Typically NO is reduced on most vehicle's by the EGR system or EGR valve. On your Toyota 4Runner however the reduction of NOx or NO is the done by the CAT and proper fuel control; proper fuel control being the first. So as far a fuel control and Air/Fuel mixture, a smog check repair station will first have to ensure your 2000 Toyota 4Runner vehicle is in proper fuel control. This includes ensuring the oxygen sensors are working properly, the computer system is receiving the signals from the oxygen sensors, 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. At the end of the feedback test it will be know whether there is a fuel control problem causing high NO, and whether it is electronic or mechanical. The technician can further diagnose the fault. posted by SmogTips Support

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