In the case of lincoln twncar 1995, smog tested with smog test only station, dealer service dept. on 6 services gets light off, but .2 TO 19 miles drive off the light back on. Can't pass smog, with light on, though with tailpipe monitored, itpasses emmissions. only no-pass is check engine light on.
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1995 Lincoln Town Car Question: What to do if vehicle passes, twice all emission, but the check engine light on?
Answer #1patrick mannion from Greg Solow's Engine Room, March 12, 2010, 19:11Master
Tail pipe emissions are the critical part of the state emission test but the Check Engine light shows a fault in the emission system. The computer in your car tests the emission system when certain criteria is met while driving or even when the ignition switch is turned on. A scan tool is needed to retrieve the codes stored in the computer in your car and the fault fixed.