The California Air Resources Board has approved for sale two aftermarket replacement catalytic converters to meet the dramatically rising public demand prompted by the state's Smog Check program, Walker Manufacturing of Grass Lake, MI, and Echlin Inc. of Branford, CT, were granted permission to sell newly manufactured replacement converters after tests showed their use did not cause an increase in pollution levels, compared to use of factory original equipment. The newly-approved aftermarket converters, with an estimated price tag of $100, are expected to provide a low-cost alternative to replacement of factory-original equipment that often costs $200 to $300 each. ARB officials estimate that sales of replacement catalytic converters have jumped 150 percent -- to 80,000 a year ---- since the Smog Check began last March. As car owners replace converters that have been illegally removed or poisoned through the illegal use of leaded gasoline, the public demand has out stripped the available supply at wrecking yards in some parts of the state. Under the Smog Check program, more than 20 million cars and light trucks in California's urban areas are tested once every two years to insure that their pollution levels are within acceptable limits before their registration is renewed. Repairs for most cars that fail the test usually include minor adjustments, tune-ups or fixing of small components and are limited to a $50 cost. Those cost limits do not apply, however, to cars that fail the test because of tampered or modified anti-smog systems. In those cases, motorists must pay