I have a 2003,Frontier, v-6, automatic. It is a US car but is currently in Costa Rica. My HC and CO were close to zero at idle. At higher RPM HC was still low, but CO wouldn’t pass. I don’t have the exact numbers because the truck is not now with me. I’m hoping someone might be able to tell me if there are common causes for these types of readings. Next time I go to Costa Rica I plan to bring common parts with me, but am trying to avoid buying things I don’t need. After the failed readings I replaced the spark plugs and CO at higher RPM came down, but not enough to pass. I am planning to get a new PCV valve, O2 sensors and maybe plug wires, but am interested in insights from more knowledgeable people. Thank you!