Skip the auto shop - Our mechanics make house calls

Q: Vehicle won't pass emissions test

asked by on

My vehicle won't pass the emissions test. It failed the CO GPM & NOx GPM.

A: Emissions tests analyze three main exhaust ...

Emissions tests analyze three main exhaust gas components: hydrocarbons (HC), carbon monoxide (CO), carbon dioxide (CO2). In some places, they also look at oxides of nitrogen (NOx). Excessive CO is the result of a rich fuel mixture and can only occur when combustion has taken place. For example, when a cylinder misfires, CO cannot be produced since the hydrogen and carbon in the fuel have not been separated. NOx on the other hand, results from combustion temperatures that are too high. A failed EGR valve is often the cause of excessive NOx readings. You may have two separate issues, or your catalytic converter may have failed. Your Check Engine Light is likely on, which may provide a clue. I suggest having a trained professional, such as one from YourMechanic, give a complete inspection of the vehicle and determine what needs to be repaired.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Save up to 30%

Get a quote

What others are asking

Q: Why won't my truck run?

This could be a few different things. The first thing to do check is to check if the engine oil is not low and that there is oil pressure on the gauge. A loss of oil pressure will shut off...

Q: Suspension is "loose"

The term "suspension is loose" is most likely the mechanics way of saying that you have worn components in the front end that would cause the alignment to not be able to be set to specifications. He might of seen...

Q: On a 81 through 82 model mx2 lock out converter Th350 on the 4 pin connector the two wires I would use would be A+ - B-- terminal

Hello. For one, your van came with a 4L60E. This is a four-speed, electronically controlled transmission. The TH350 is a 3-speed hydraulically controlled transmission. This swap is just not doable in my opinion. Even if you could complete the swap,...

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...