Close
Car Questions
RepairPal is your advocate for car care advice and guidance

My truck is failing smog check due to high CO, what might cause this?

(2003 Nissan Frontier)
in Downey, CA on February 18, 2011
My truck has passed with flying colors on everything by the CO, it is about twice the limit for CO. The vacumm hose and O2 sensors have been replaced, to very little effect. The truck runs great, the tail pipe is clean, and there are no diagnostic codes in the computer.

finally got the Frontier to pass smog. Pulled the plugs and cleaned the piston tops, flushed all the fuel lines. After this it finally had the CO come down to acceptable levels.
Displaying 1 answers & 0 comments
Popular Answer
on June 17, 2011
My mechanic ended up cleaning the top of the pistons and flushing the fuel lines. This removed the carbon build up inside the cylinder. Truck then passed the smog test.
RepairPal estimates are guaranteed at over 2,000 quality certified locations nationwide. Learn more

Similar Questions

View answers to similar questions from RepairPal's community of auto experts and enthusiasts.
I haven’t had any issues until now but the heater stopped working. I turn the knob for the fan but nothing is coming on
I'm think starter relay or ignition relay
Didn't find what you were looking for?