Check engine light

How to read it

The symbol is an engine drawn in outline. According to the California Air Resources Board, the light will typically display the words "Check Engine" or "Service Engine Soon" and often includes an engine symbol. Ford's F-150 manual calls it Service Engine Soon: lit with the engine running, it means the on-board diagnostics system has detected a malfunction of the vehicle emission control system, and flashing, that an engine misfire may be occurring.

Also searched as: engine light, malfunction indicator lamp, MIL.

Why is my check engine light on?

Ford's F-150 manual says the light means the on-board diagnostics system has detected a malfunction, and that temporary conditions can turn it on: running out of fuel, poor fuel quality or water in the fuel, a fuel fill inlet that has not closed properly, or driving through deep water. The California Air Resources Board says many different problems can cause it, so it is hard to say how serious any one is.

What does a flashing check engine light mean?

Ford's manual says a flashing light means an engine misfire may be occurring, and that the higher exhaust temperatures could damage the catalytic converter; it says to avoid heavy acceleration and deceleration and to have the vehicle serviced immediately. The California Air Resources Board says a blinking light shows a malfunction that could be damaging the catalytic converter, and that many manufacturers recommend service as soon as possible.

Can you keep driving with the check engine light on?

For a steady light, Ford's manual says to have the vehicle serviced at the first available opportunity, and that continued driving with it on can mean higher emissions, lower fuel economy, rougher running and more costly repairs. The California Air Resources Board says most manufacturers advise service as soon as conveniently possible, and that extended driving without a repair could damage other components.

How it goes out

Ford's manual says that once a temporary cause is gone, the light should stay off after three driving cycles, each a cold start followed by mixed city and highway driving.

Reading the codes

Federal rules require the OBD system to store a trouble code for the fault that turned the light on, and make that data available through the car's standardized diagnostic connector without any device only the manufacturer supplies. The California Air Resources Board says properly trained and equipped independent shops can use it and make repairs just like dealers. Ford's manual warns against connecting wireless plug-in devices to the connector, and says to let only repair facilities that follow its instructions connect their equipment.

Differences by country or standard

The U.S. Environmental Protection Agency requires all 1996 and newer passenger cars and trucks sold in any state to meet its OBD requirements, which differ slightly from California's, according to the California Air Resources Board.