Exhaust System Repairs – Emissions System Repairs

The automobile gets power from a series of controlled explosions in cylinders which drive pistons up and down, a process commonly known as internal combustion. As the pistons go up and down they turn a crankshaft, and the rotational kinetic energy of the crankshaft is transferred to the wheels through the drivetrain (a series of gear parts and shafts that ends with the wheels turning forward).

When any organic material is burned, including the air-fuel mixture burned during internal combustion, the by-product of that combustion is gas. Here the word “gas” is used in the chemically correct sense, since the “gas or gasoline” that you use to fuel your vehicle actually starts as a liquid when you fill it up at the station. Since the cylinders within an engine are a very small, confined space, the gas must have a place to escape so that the engine doesn’t build up pressure and explode. It escapes through the Exhaust System of the vehicle, which is a series of parts starting with the exhaust valves of the cylinders in the engine and ending with the tailpipe.

Engine exhaust can be loud (it’s the byproduct of multiple mirco explosions after all), so another function of the exhaust system besides diverting gas from the engine is to reduce sound. Also the gas is not good for the environment so there is another system that converts this gas into less harmful substances, which is called the Emissions System.

Some people might use the words “exhaust” and “emissions” interchangeably, but technically “exhaust” refers to the combined gas as a whole (the sum of all it’s parts), and emissions refers to each of the compounds within the gas. Vehicle emissions include some harmless substances such as water, heat and oxygen and some harmful ones such as hydrocarbons (HCs), carbon monoxide (CO) and nitrogen oxide (NOx). So the emissions system focuses on each of these compounds, and emissions testing is also measuring each of these compounds. Yet, the overall goal of “emissions” is to make the exhaust cleaner.

The major parts of the exhaust system include the exhaust manifold, oxygen sensor, exhaust downpipe, catalytic converter, resonator, muffler and tailpipe. The catalytic converter converts harmful carbon monoxide and hydrocarbons to water vapor and carbon dioxide. Other converters, especially those found in diesel engines, also reduce nitrogen oxides (NOx). The muffler serves to reduce exhaust noise. A diesel exhaust system also includes a particulate filter.

Subsystems of the emissions system include the Evaporative Control (EVAP) system, the Exhaust Gas Recirculation (EGR) system, and the secondary air injection system. The Evaporative Control (EVAP) System captures any raw fuel evaporating from the fuel storage system and purges these fuel vapors back into the combustion process, improving fuel efficiency. The EVAP system includes the charcoal canister, canister vent valve, fuel vapor lines, and canister purge valve.

The Exhaust Gas Recirculation system recycles a small amount of exhaust gas from the exhaust system and mixes it with the intake manifold air going into the combustion chambers which limits combustion temperatures and prevents formation of NOx. The Secondary Air Injection System pumps fresh air into the exhuast system to help reduce exhaust emissions. The major parts include the air pump, air injection control valve and powertrain control module.

Emissions Testing In Arizona

In the Phoenix Metropolitan area there are specific requirements for emissions testing. Some of the factors for these regulations include the year the vehicle was manufactured and the population density of where the vehicle is driven. Older vehicles usually need to be tested every year, as well as any diesel engine. Newer vehicles may need to be tested every two years.

Your vehicle registration renewal notice will inform you if you need a test. It is best to have your vehicle tested right away so that any failure can be repaired before the registration is expired. If your vehicle fails an emissions test then the registration cannot be renewed until the repairs are performed and it passes an emissions test. Go to ADEQ and myAZcar.com for information on emissions testing requirements.

Any vehicle made in 1996 and later has OBD-II compliance (on-board diagnostics). This means the vehicle is capable of self-testing all emissions components. So a test on newer vehicles only requires a diagnostic scanning device, which is plugged into an OBD-II input on the vehicle below the steering wheel. This checks for any faults and makes sure all readiness monitors are completed. If you’ve recently replaced your battery, or disconnected the cable for any reason, the emissions monitor will reset. Then the vehicle will have to be driven under certain conditions to complete a drive cycle. A drive cycle can vary by make and model. If you need to complete a drive cycle you might have to search for instructions on your specific vehicle. OBDii.com has instructions for General Motors and Ford vehicles; MyAZcar.com has a general drive cycle description that may work for your vehicle.

Vehicles made prior to 1996 are checked on a DYNO (short for dynamometer). They attach a hose to the exhaust pipe and monitor the exhaust.

If you happen to fail an emissions test, then bring your vehicle to the shop with the emissions test results sheet.

Are you a business owner with a fleet? Fleet Auto Repair Services includes emissions repair.

Exhaust System Maintenance

The exhaust system is inspected during routine maintenance checks with every oil change (about every 5,000 miles) and at each landmark mileage check at 30K, 90K and 100K miles. During a test drive the technician will note any signs or symptoms that might be related to the exhaust system as well as any dashboard warning lights that could indicate a problem with the exhaust system, including the Check Engine Light, Catalytic Converter Light or Lambda Sensor Warning Light. The technician will also inspect all parts of the exhaust system which can be visually inspected without disassembly.

Beyond routine maintenance checks you could also change the oxygen sensor every 60,000 miles or at the mileage which the vehicle’s manufacturer suggests. This can improve your gas mileage and more than makes up for the cost of the sensor.

If you drive a diesel vehicle then your Diesel Emissions Fluid or Diesel Exhaust Fluid (DEF) should be refilled with every oil change.

DIY Maintenance Tips For The Vehicle Owner

The worst enemy of the exhaust system is corrosion (rust). There’s no snow here in the Chandler-Gilbert area throughout the year, but if you ever spend time on salted snowy roads in the winter, then you should have the underside of your vehicle washed as frequently as the top.

There are other suggestions out there about preventing rust, including paints, waxes and other coating to separate the system from the environment, but if you’re considering any of that then talk to us first. The problem with any of these “solutions” is the heat produced by the exhaust system, which usually burns it off.

Warning Lights For The Exhaust System Which Merit Inspection & Repair

If the following warning lights come on then you will need an inspection and repairs for the exhaust system or emissions system.

Check Engine Light

If this light is illuminated then your vehicle will not pass an emissions test. It could be anything related to the engine, the ignition system or the exhaust system. Learn more about the Check engine Light Diagnostic.

Catalytic Converter Warning Light

Likely your catalytic converter is overheating, but it could possibly come on for other reasons. The Check Engine Light may come on at the same time since it monitors anything that can affect emissions, but this light is specific to the exhaust system.

Lambda Sensor Warning Indicator

The exhaust gas oxygen sensor is dirty or inoperative.

Diesel Engine Exhaust System Warning Lights

Diesel engine vehicles have a unique set of warning lights that are not found in regular gasoline vehicles.

Diesel Particulate Filter Warning

This should turn green while driving which indicates that the DPF filter is regenerating properly. If it’s red then it needs to be serviced immediately.

Diesel Exhaust Fluid Low Indicator

The diesel exhaust fluid needs to be topped off.

AdBlue Service Light

AdBlue is a specific type of diesel exhaust fluid. If the light has a wrench instead of a fluid drop then it needs to be serviced immediately.

Water in Fuel Indicator

The filter which helps remove water from the fuel needs to be changed. The filter system may be called the Diesel Fuel Conditioner Module by some manufacturers. This is technically part of the fuel system but it can affect emissions.

Exhaust System Signs That Merit Further Inspection & Repair

• Visible rust on any part of the exhaust system – rust can be present at any time, the technician will suggest when it’s severe enough
• Decrease in gas mileage efficiency
• Warning indicator lights are illuminated, including the Check Engine Light, Catalytic Converter Light or Lambda Sensor Warning Light
• Your vehicle does not pass emissions testing

Exhaust System Repairs & Emissions System Repairs

As previously stated, when you receive your vehicle registration renewal notice make sure you get it emissions tested in time to have it repaired if needed before the current registration expires.

Also, worth noting again, the worst enemy of the exhaust system is rust. If you commonly drive short trips less than 15 miles a trip, then consider using stainless steel parts for the exhaust system whenever they have to be replaced. (And if you drive on salty roads in the winter then wash the underside as frequently as the top side to reduce the formation of rust).

When it comes to mufflers you get what you pay for. If your muffler ever needs to be replaced consider an OEM muffler or a high quality name brand muffler.

Never let a mechanic tell you that you don’t need a catalytic converter. It’s illegal in most states not to have one.

The following is a more complete list of emissions and exhaust repairs and services: