Ford 2003 Mustang Owner's Manual page 7

Instrumentation
Safety belt
Momentarily illuminates
when the ignition is
turned to the ON
position to remind you
to fasten your safety belts. For more information,
refer to the Seating and safety restraints chapter.
Door ajar
Illuminates when the
ignition is in the ON or
START position and
any door is open.
Service engine soon
Your vehicle is
SERVICE
ENGINE
equipped with a
SOON
computer that monitors
the engine's emission
control system. This
system is commonly known as the On Board
Diagnostics System (OBD II). The OBD II system
protects the environment by ensuring that your
vehicle continues to meet government emission
standards. The OBD II system also assists the
service technician in properly servicing your vehicle.
The Service Engine Soon indicator light illuminates
when the ignition is first turned to the ON position
to check the bulb. If it comes on after the engine is
started, one of the engine's emission control systems
may be malfunctioning. The light may illuminate
without a driveability concern being noted. The
vehicle will usually be drivable and will not require
towing.
What you should do if the Service Engine Soon
light illuminates
Light turns on solid:
This means that the OBD II system has detected a
malfunction.
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