On board diagnostics (OBD-II)
Your vehicle is equipped with a computer that
monitors the engine’s emission control system. This
system is commonly known as the On Board
Diagnostics System (OBD-II). This 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.
When theCheck Engine/Service Engine Soonlight
illuminates, the OBD-II system has detected a
malfunction. Temporary malfunctions may cause
yourCheck Engine/Service Engine Soonlight to
illuminate. Examples are:
1. The vehicle has run out of fuel. (The engine may
misfire or run poorly.)
2. Poor fuel quality or water in the fuel.
3. The fuel cap may not have been securely
tightened.
These temporary malfunctions can be corrected by
filling the fuel tank with good quality fuel and/or
properly tightening the fuel cap. After three driving
cycles without these or any other temporary
malfunctions present, theCheck Engine/Service
Engine Soonlight should turn off. (A driving cycle
consists of a cold engine startup followed by mixed
city/highway driving.) No additional vehicle service is
required.
If theCheck Engine/Service Engine Soonlight
remains on, have your vehicle serviced at the first
available opportunity.
Readiness for Inspection/Maintenance (I/M)
testing
In some localities, it may be a legal requirement to
pass an I/M test of the on-board diagnostics system.
If your“Check Engine/Service Engine Soon”light is
on, refer to the description in theWarning lights
and chimessection of theInstrument cluster
chapter. Your vehicle may not pass the I/M test with
the“Check Engine/Service Engine Soon”light on.
2004 Mustang(mus)
Owners Guide (post-2002-fmt)
USA English(fus)
Maintenance and Specifications
193
