Tip & How-To about Chevrolet 1500

Failing emissions testing due to high NOX (oxides of nitrogen)

I have seen several people posting emissions failures due to high NOX (oxides of nitrogen). Nox is created when the engine's internal combustion temperature gets to high.

Two reasons this can occur is improper coolant levels and a malfunctioning egr system. The egr system injects exhaust gas from the exhaust and uses it to line the cylinder walls.This in turn reduces the combustion chamber size and internal combustion temperatures. Ultimately this reduces the amount of NOX created. These systems functioning properly can be the difference in passing or failing your emissions testing because of high NOX ppm.

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I have a 1999 Chevy S10 2.2L 4Cyl extreme. I can not find or locate the EGR Valve any where,I am pretty sure it does not have one, I wanted to confirm or discuss this with a fixian expert like myself?


Doesn't have EGR valve . How many miles on the truck ?
What Causes High NO (NOx)? Nitrogen Oxide or NO is created when an engine's combustion chamber temperature reaches over 2500F. Vehicle manufacturers have designed several systems, which when working properly, lower nitric oxide emissions. Below are common failures which may cause your car, truck, van, suv, or motorhome to produce high high nitric oxide. 1. Lean Fuel Mixture - Lean fuel mixtures cause high NOx. A lean fuel mixture exists when less fuel then required is delivered to the combustion chambers or when more air then necessary is added to the fuel. In either case the lack of gasoline needed to cool the combustion chambers down is not present. Combustion temperatures increase causing high nitric oxide emissions. A lean fuel condition may be due to a vacuum leak/s and/or defective fuel control components, such as the Air Flow Meter, Engine Coolant Temperature Sensor, and O2 sensors. Read about Oxygen Sensor.
2. Defective EGR System- The Exhaust Gas Recirculation system is designed to reduce NO. The EGR system consists of an EGR valve, EGR pressure sensor, vacuum hoses, and one or more vacuum switching valves or solenoids. Later model vehicles may be equipped with electronically controlled EGR valves, which do not require vacuum lines or switching solenoids. Electronic EGR systems will have these components built in.
The EGR system's job is to re-route a small amount of exhaust gas back into the intake manifold to help reduce combustion chamber temperatures. As mentioned above NOx is created when combustion chamber temperatures reach above 2500F. By recirculating exhaust gas back into the intake, a small amount of the air/fuel mixture is replaced with inert gas, reducing combustion temperatures. Read about EGR System.
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3. Defective Catalytic Converter (CAT) Some vehicle manufactures have designed their cars to operate without EGR valves. Non-EGR equipped vehicles rely heavily on the Catalytic Converter to assist in the reduction of NO. These vehicles have tendencies to develop CAT problems sooner then those which are equipped. If you own a non-EGR equipped vehicle, and have failed the emissions test for high NOx, pay close attention to the Catalytic Converter. Read about Catalytic Converter
4. High Engine Mileage - Over an engine's lifetime, carbon build-up develops in the engine's combustion chambers. The more miles on your engine, the more carbon build-up on the pistons, cylinder heads and valves. Carbon build-up decreases the available space for the air/fuel mixture to combust, and causes higher cylinder compression. High compression results in high temperatures and high NOx. Keep in mind this problem is usually seen in vehicles with over 150,000 miles which have been poorly maintained. The solution to this problem is called De-Carbonizing. It usually costs around two labor hours at a smog check repair station. It will remove a good amount of carbon out of an engine. This will increase combustion space, lower compression and lower NOx.
5. Engine Overheating - Inadequate engine cooling can will high NOx. If your vehicle's cooling system is not working efficiently, (i.e. bad radiator, thermostat, hoses) high NOx will be created. Remember high NOx nitric oxide is created when an engine's combustion chamber temperatures reach over 2500F. You will want to make sure your vehicle's cooling system is working properly, and your vehicle's temperature gauge is always indicating normal.

Feb 24, 2018 | 1999 Chevrolet S-10 Pickup

1 Answer

what a erg or egr what does it do


In internal combustion engines, exhaust gas recirculation (EGR) is a nitrogen oxide (NOx) emissions reduction technique used in petrol/gasoline and diesel engines. EGR works by recirculating a portion of an engine's exhaust gas back to the engine cylinders.

Exhaust gas recirculation - Wikipedia

https://en.wikipedia.org/wiki/Exhaust_gas_recirculation
egr what does it do Google Search

Nov 18, 2017 | Cars & Trucks

2 Answers

what is the egr system


EGR stands for Exhaust gas recirculating system

Apr 07, 2012 | Cars & Trucks

1 Answer

what is the meaning of a failing test with NOx(ppm)


Oxides Of Nitrogen (NOX)

Above 2500 degree engine combustion temperature
nitrogen bonds to oxygen to form NOX

The EGR Valve is supposed to allow a certain
amount of exhaust gases into incoming air to
control high combustion temperature and control
NOX

Bad Egr Valve
Engine operating too hot
Cat too cool at inspection station
Fuel mixture issues
PCV issues
O2 Sensor issues
Injector issues
Ignition issues

Jan 30, 2011 | Toyota Previa Cars & Trucks

1 Answer

Keep failing emissions test due to high no levels. I have replaced the oxygen sensor and do not know what could be causing this problem.


NOX is created when the engine's internal combustion temperature gets to high.In addition to maintaining proper coolant levels.The egr system may be malfunctioning.The egr valve uses spent exhaust gases to line the cylinders walls reducing internal combustion temperature and reducing the amount of NOX produced.

Jun 18, 2010 | Cars & Trucks

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