1212 Golf Road

Waukegan, Illinois

(847) 623-9609

Your car didn't pass the emissions test? Then as you know, If your vehicle failed the Illinois emissions test, it needs to be repaired and re-tested.  As you also know, it's a much more complicated testing procedure than that which used to be done by simply taking a reading from your exhaust tailpipe.  There are many things that can make your car not pass this more precise test, and a tune-up doesn't always solve the problem.    

New OBDII Testing

The purpose of the On Board Diagnostic (OBDII) system on vehicles is to ensure that the emission control system and other engine-related components are operating properly. Monitors located with the Engine Control Module of the car use information from various sensor circuits to indicate overall operation of the fuel, engine, ignition and emission systems.  Monitors don't indicate a specific component problem, but that there is an implied problem with one of the systems that must be diagnosed...that's when that "Service Engine Soon" indicator comes on the dash (technically called the Malfunction Indicator Lamp, or MIL)!

By 1996, most vehicles had become OBDII-compliant and with that, diagnosing & repairing driveablity problems got much more complicated.  Once the diagnosis & repair are completed, in order to be able to pass the emissions test, we can't just clear those codes from the computer to turn out that MIL.  The proper way to clear codes and re-set the MIL  is to drive the vehicle, following the manufacturer's exact sequence of various engine & vehicle parameters, until the vehicle turns the MIL out.  In other words, a specific Drive Cycle is required for the vehicle's readiness monitors to be set. 

Recent legislation has allowed the Illinois EPA to conduct OBDII system testing and use those test results to pass the emissions test. In essence, the vehicle's computer memory is being tested for codes that may cause high engine or evaporative emissions.   This test now replaces traditional exhaust emission tests for most 1996 and newer model vehicles.  The "Motorist's Choice" option that allowed customers to choose (or "fallback" to) an exhaust test has expired.  Heavy-duty trucks aren't required to have OBDII systems, and thus, still receive the appropriate exhaust test.   

There is a difference between vehicles that get rejected and vehicles that fail.   If your car gets rejected, it's because of those readiness monitors mentioned above. A vehicle is rejected if three or more noncontinuous monitors are reading "not ready." As mentioned, clearing codes resets all readiness monitors to "not ready" and the process of setting a sufficient number of the monitors to "ready" can take some time (and patience!).

If you car is older than 1996, it will be IM240-tested.  That's the test where they drive it on the dynamometer  (the rollers in the floor) and obtain hydrocarbon and carbon monoxide readings.   In order to pass an IM240 test, every vehicle must minimally have:

• fuel control with no misfires
• a functioning oxygen sensor(s)
• an 80% efficient catalytic converter

Information about "Emissions"

Incomplete burning of the engine fuel causes the formation of hydrocarbons (HC) and carbon monoxide (CO).  Excessive combustion chamber temperatures can cause the production of oxides of nitrogen (NOx).  Unburned gasoline from the fuel system is responsible for large amounts of HC.  This combination of HC, CO and NOx, if released into the atmosphere, could cause serious air pollution problems.   Currently, the Illinois emissions test does not test NOx levels; only HC and CO are measured. 

Environmental protection laws have attempted to reduce pollutants by requiring the use of certain exhaust and emission control devices that control the amount of pollutants (gases & particulates) that engines produce.  These emission control components also, unfortunately sometimes, affect the performance of your car's engine.   Many of the ignition and fuel delivery components on both fuel-injected and carbureted models have also been developed to control emissions. 

Here is a list of some of the major devices and a brief description of how they work.  Your car may have a few or many of these devices, as well as additional components not listed here.  Many of the systems are interrelated. 

(exhaust gas recirculation)

Recirculates exhaust gases back to the engine where they are burned again.  The amount of exhaust gas fed into the intake manifold is automatically controlled by the EGR valve which is operated by engine vacuum, electrical signals or a combination of both.  When operating correctly, the EGR valve is opened when the engine is under light and moderate loads.  During idle and wide open throttle conditions,, the EGR valve remains closed. 

 Closed Loop System

Closed loop systems use an oxygen sensor in the exhaust stream to constantly monitor the amount of oxygen in the exhaust.  Signals from the oxygen sensor, as  well as other sensors, cause the car's main control unit to adjust the air-fuel mixture, engine timing, EGR action, etc. to provide the lowest possible engine emission levels. 

Part of the exhaust system, it is located between the exhaust manifold and the muffler.  As hot exhaust gases pass through the converter, they come into contact with a catalyst coating inside the converter.  This causes a chemical reaction which changes the hydrocarbons and carbon monoxide into harmless water vapor and carbon dioxide.  

Uses a system of tubes to route a stream of fresh air into the exhaust just as it passes out the exhaust valve.  This provides extra oxygen which causes further burning of the exhaust gases.  This additional burning reduces the amount of hydrocarbons and changes a sizeable portion of the carbon monoxide (poisonous) into carbon dioxide (nonpoisonous) gas.

(evaporative emission control)

Traps vapors from the fuel system and redirects them to the engine, where they are stored in a charcoal canister.  Instead of being released into the atmosphere, these fumes are burned in the engine when the engine is restarted. 

Picks up "blow-by" gases that have escaped into the crankcase from the combustion chambers and returns them to the engine to be burned.

Uses hot exhaust gases to maintain the flow of warm air into the engine. This allows for a more combustible mixture that requires less fuel and burns more completely.

All of these systems require a series of inspections and diagnostic procedures in determining the exact cause of a vehicle not passing the emissions test.  The diagnosis and repair of vehicles that fail an emissions test can involve the repair or replacement of multiple components from multiple systems that need to work together and can be very challenging.  It's usually a one-step-at-a-time process.

We do a lot of emission repair work at Strang Automotive, and we take great pride in our repair success rate at getting vehicles to pass the emissions test.  We take most cars back to the emission test lane for you after repairs are completed and make sure they pass.  That way when you pick your car up, it's all been taken care of, and you know the job has been done successfully before you leave.