Inspection Info
What is Variability?
If your vehicle has failed an AirCare inspection and then passed without any repair working being done, or if it has failed again in a different area or with much different readings, your vehicle needs emissions repairs.
Although it is common to believe that variation in emissions readings is the fault of the testing equipment, it is the vehicle that is varying - not the exhaust gas analyzers. No vehicle will produce exactly the same emissions readings on back-to-back tests. However, if a vehicle's engine is in good mechanical condition, at its normal operating temperature, and with all of its original emissions control equipment in place and operating properly, it will consistently produce readings within a narrow range, well under the AirCare "maximum allowable" limits.
What Causes Variability?
The composition of the exhaust gas coming out of the tailpipe can be influenced by many factors. If any part of the combustion process is negatively influenced by an emissions defect, your vehicle can exhibit unstable or variable readings either above or below the test limits.
Modern engines are controlled by computers that determine the right fuel mixture and ignition timing for a wide range of engine operating modes. To do this, the computer needs to collect information from a number of sensors telling it the engine speed, load, throttle position, air flow and exhaust gas oxygen content. Defective sensors, wiring faults or corroded connections can produce intermittent false inputs to the computers. When such faults are present, emissions are high; when they're not, everything may look perfect.
Is the AirCare Reading Accurate?
The analyzers used to test vehicles at AirCare are both accurate and reliable. Emissions analyzers in the AirCare lanes are calibrated every business day and the zero level is checked and re-set between each test. Audits are performed on the analyzer using federal government certified blends of HC, CO, NOx and CO2, in order to ensure that the analyzer will accurately read the concentration of any gas presented to it.
The dynamometer used for the driving test portion of the inspection is calibrated monthly to ensure that the desired test speed and load is delivered every time.
Every precaution is taken to ensure that the equipment is ready and able to perform the test. The one big variable that we have no control over, however, is your vehicle. You can be assured, that the reading on your AirCare inspection form accurately reflects how your vehicle was performing at that moment in time.
What Do I Do If My Vehicle Has Variable Readings?
If your vehicle is failing the test but with widely-varying results, consult a qualified AirCare repair centre. The problem that is causing the failure is also causing the variability. If your vehicle passed the re-inspection without repairs, it could be that the problem which resulted in the failure is intermittent in nature or the conditions immediately prior to the test helped to mask the problem sufficiently enough to obtain a marginally passing result. In either case, you should still have the vehicle checked by a qualified technician.
Because intermittent problems may not be present when the vehicle goes to the repair shop, the diagnostic process may take more time. However, a thorough check of all systems will eventually reveal the source of the problem.
