Close
QUESTIONS

RepairPal is your advocate for car care advice and guidance

Q: Good HC and CO but high NO on emission test on 1991 Toyota Previa

Rookie cbe0621eac06868b3efe0d8d1d3611e23c60d3114864ea2ec19a68cfbd3eebab
My 1991 Previa had high HC and CO levels but good NO when first tested for emission. After refueling and added fuel injector treatment,the HC and CO levels are down (almost zero) but the NO has gone up from 433 ppm to 1939 ppm. The check engine light is also on. Could the problem be defective oxygen sensor (someone said fuel injection treatment could damage oxygen sensors) or defective catalytic converter?
No car image 94a1663db56199c5353592009e34aaa51078a2469bed068bb8d6f0ba43accf97
Get a Repair Estimate
Guaranteed by certified locations nationwide. Learn more
RepairPal estimates are guaranteed at over 1,700 quality certified locations nationwide. Learn more
You need to find what is the reason for the Check engine light coming on, once you determine that we can get you going in the right direction. Know this, high NOx is caused by too much timing advance, non functioning or restricted EGR system, exhaust leak prior to the catalyst, engine operating temperature being too high, excessively lean mixture and finally bad reduction bed in the three way catalyst. Since your HC and CO emissions are okay, you would have to look at the catalyst, but I would not until I know what triggered the Check engine light to come on. Good luck
Find Out Why Your Check Engine Light Is On
Didn't find what you were looking for?