Analysis of invalid emission testing in the California smog check program. Technical report

The report describes the results of exhaust emissions measurements reported by licensed automotive repair dealerships participation in the California motor vehicle inspection and maintenance (I/M) program called Smog Check. The results have been compared to measurements made on the same vehicles at the California Air Resources Board (ARB) laboratory. Based on an experimental program conducted by ARB the Smog Check station exhaust emission test results appear to be invalid for about 17.5% of the vehicles. The report describes the issues involved.