Authorized Emission Specialist

For immediate help, call (253) 630-8133, or schedule your emissions repair using our online system. Get compliant right away!

Understanding the Vehicle Emissions Repair Process

It is best to repair your vehicle to its original operating condition. When left unrepaired, many emission issues cause problems that are more costly than the original repairs. For vehicle owners who cannot afford to pay for full repairs, the State of Washington has a $150 waiver program. To qualify for a waiver, you must first have your car inspected. If it were to fail the vehicle emission inspection, you would need to contact a State Ecology Authorized Emission Specialist. The emission specialist would conduct $150 of diagnosis/repairs of the failure. Finally, you would need to return to the emission-testing center and provide an itemized receipt of work performed by the Authorized Emission Specialist. Vehicles with missing or tampered emission control equipment are ineligible for the waiver. This includes cold air intakes, engine swaps, power chips, oversize tires, etc.

For more information about Washington State’s motor vehicle inspection requirements, visit the Vehicle Emission Inspection Program website.

On-Board Diagnostic Systems

Since model year 1996, all cars and light trucks sold in the United States are OBD-II compliant. They have an On-Board Diagnostic System that monitors engine and emission system functions and efficiency. They also have a computer controlled fuel injection system that uses sensors to calculate when and how long to open the fuel injector for each cylinder. Most modern cars and trucks have no manual adjustments to change fuel ratio. The computer makes all of the adjustments based on the input of the sensors. Therefore, an emission repair on these vehicles almost always involves diagnosing the problem and replacing the defective parts.

When the OBD-II system detects a problem, it will leave a code stored in memory, and it may turn on the check engine light. The code in memory can be read by the use of a scanner, and it can tell the technician what part of the vehicle is causing a problem. It does not tell the technician exactly what the specific repair will be; it usually requires the technician to do additional diagnosis.

For example, a code PO171 means that the oxygen sensor on bank 1 (inline 4 and 6 cylinders only have 1 bank, V6 and V8 engines have 2) has detected a lean condition. It does not tell the technician why it is lean. Possible causes are a defective Mass Airflow Sensor, Low Fuel Pressure, Vacuum leaks or various other problems. This is why the testing of components is necessary.

The OBD-II System monitors misfire, catalyst, oxygen sensor, exhaust gas recirculation (EGR), secondary air, evaporative leak check, and fuel systems. A failure in any one of these systems will cause an emissions failure. Many cars have multiple failures.

The Oxygen (O2) Sensor

The oxygen sensor monitors the level of O2 in the exhaust, so an onboard computer can regulate the air/fuel mixture to reduce emissions. The sensor is mounted in the exhaust manifold downpipe(s), before the catalytic converter or between the exhaust manifold(s) and the catalytic converter(s). It generates a voltage signal proportional to the amount of oxygen in the exhaust.

The sensing element on nearly all oxygen sensors in use is a zirconium ceramic bulb, coated on both sides with a thin layer of platinum. The outside of the bulb is exposed to the hot exhaust gases, while the inside of the bulb is vented internally through the sensor body or wiring to the outside atmosphere.

When the air/fuel mixture is rich and there is little O2 in the exhaust, the difference in oxygen levels across the sensing element generates a voltage through the sensor’s platinum electrodes: typically 0.8 to 0.9 volts. When the air/fuel mixture is lean and there is more oxygen in the exhaust, the sensor’s voltage output drops to 0.1 to 0.3 volts. When the air/fuel mixture is perfectly balanced and combustion is cleanest, the sensor’s output voltage is around 0.45 volts.

The oxygen sensor’s voltage signal is monitored by the onboard engine management computer, to regulate the fuel mixture. When the computer sees a rich signal (high voltage) from the oxygen sensor, it commands the fuel mixture to go lean. When it receives a lean signal (low voltage) from the oxygen sensor, it commands the fuel mixture to go rich. Cycling back and forth from rich to lean averages out the overall air/fuel mixture to minimize emissions and to help the catalytic converter operate at peak efficiency, which is necessary to reduce hydrocarbon (HC), carbon monoxide (CO) and mono-nitrogen oxides (NOX) levels even further.

The speed with which the oxygen sensor reacts to oxygen changes in the exhaust is very important for accurate fuel control, peak fuel economy and low emissions. The air/fuel mixture in an older carbureted engine does not change as quickly as that in a throttle body fuel-injected vehicle. So, response time is less critical. In new engines with multipoint fuel injection, the air/fuel mixture can change extremely fast, requiring a very quick response from the oxygen sensor.

Call Kent Auto Repair, Your Authorized Emission Specialist

Let Kent Auto Repair service all of your vehicle emission inspection needs. Call (253) 630-8133, or schedule your emissions repair online. Get compliant right away!