Repair Info - Emissions Repair Explained
Requirements for Effective Diagnosis and Repair
When a vehicle fails an emissions test, it means that a defect exists. The defect may be a broken or malfunctioning part, or, on older vehicles, it may be that a part is adjusted incorrectly. Identifying and correcting the defect in the most cost-effective manner should be your objective. Hopefully, this is also the objective of the technician tasked with diagnosing and repairing your vehicle.
Some diagnostic and repair technicians are more effective than others. In this section you will learn the reasons for this and you will gain an insight into the logical processes that should be used by the technician diagnosing and repairing your vehicle.
Logical and Consistent Diagnostic Procedures
Good technicians consistently apply logical procedures when diagnosing vehicles that have failed their emissions test. What this means in a nutshell is, they don't take unnecessary actions and they don't skip steps or make assumptions about any aspect of the vehicle that can affect its emissions.
Let's look at an example:
Technician A is diagnosing a 70's vintage pickup that has failed for excessive CO. Technician A knows that CO is directly related to how much fuel the engine is burning and that ignition system components (spark plugs, wires, etc.) have no effect on CO emissions so they are irrelevant to the diagnosis and repair of this vehicle.
Technician B is also diagnosing a 70's vintage pickup that has failed for excessive CO. Technician B knows that spark plugs and other ignition components wear out more frequently on older vehicles so he recommends new spark plugs in his diagnostic conclusion.
Here's another example:
Technician A has determined that a 1996 vehicle is maintaining correct fuel control when idling. To be certain that fuel control is being maintained under other operating conditions, he performs additional fuel control tests during a road test at different speeds.
Technician B has also determined that a 1996 vehicle he is working on is maintaining correct fuel control when idling. Based on that finding he assumes that the vehicle is maintaining proper fuel control all the time and looks elsewhere for the cause of the high emissions.
As you may have guessed, Technician B is BAD. In the first example he wastes time and money on repairs that have nothing to do with excess CO emissions. In the second example, he makes an assumption regarding the vehicle's ability to maintain fuel control under all operating conditions. As a result he may be looking past the actual defect and end up wasting a whole bunch of time and effort (and perhaps your money) testing other items before he eventually comes back to properly checking fuel control.
Another common oversight that a technician may make is to not properly test the efficiency of the catalytic converter. Proper testing of the catalytic converter requires measuring and comparing emissions going in to the catalytic converter and the emissions coming out of it. For a complete explanation of this procedure, see Catalytic Converter Testing.
As a consumer, you should know that some elements of emissions diagnosis can be quite challenging. You should also know that when diagnosing vehicles that have failed their AirCare emissions inspection, AirCare Certified Technicians can obtain expert technical assistance through a telephone hotline. For the more challenging problems, this is a distinct advantage.
