That little light on your car dashboard that sometimes comes on and says "check engine" or "service engine soon" is known in industry parlance as the idiot light. In 1996, when standards known as On-board Diagnostics II were fully phased in, the light was programmed to illuminate when there was evidence of a potential problem with the car's emission system.

What in an earlier model might have indicated a serious maintenance problem is now set to go off just because a gas cap might be loose or an oxygen sensor -- which merely double-checks that the controls are operating properly -- had failed. Experts say the light plays little if any role in safety or emission controls.

Yet over the past several years, the Environmental Protection Agency has brought enforcement actions against GM, Ford and Honda claiming they "illegally installed complex electronic devices in their automobiles that defeat the emission controls systems required by law."

• Critics say no one told drivers the idiot light had changed from warning about maintenance to a pollution warning.

• They say regulators want drivers to think they have a serious problem when the light goes off -- to trick them into getting their emissions systems checked.

• Moreover, according to a GM study, 99 percent of new car owners can expect to see at least one false warning in their first 10,000 miles, due to the excessive sensitivity programmed into their onboard computers.

Toyota refused to pay a fine of up to $100 million for tampering with emissions controls when tests showed its computer program didn't give enough alarms, so the Justice Department launched a $60 billion suit last week on behalf of the EPA.

Source: Holman W. Jenkins Jr., "Who Controls the Idiot Light?" Wall Street Journal, July 21, 1999.