Do you drive a 

1996 or newer car 

or light truck? 
I

f so, you'll be glad to know that 

your vehicle is equipped with an 

early warning system that could 

How does the 

system work? 

Today’s vehicles are highly 

sophisticated and efficient. All 

1996 and newer cars and trucks 

have an advanced powertrain control computer that uses second 

generation on-board diagnostics 

(OBD-II) technology to manage 

and monitor the operation of the 

engine, transmission, and emissions control components. OBD keeps your engine running at peak efficiency and will alert you when repairs are needed. 

How do I know the OBD system is working correctly? 

When you turn on the ignition, the “Service Engine Soon” or “Check 

Engine” light should flash briefly, indicating that the OBD system is 

ready to scan your vehicle for any malfunctions. After this brief flash, 

the light should stay off while you drive as long as no problems are 

detected. 

save you time, money, and 

fuel in addition to helping 

protect the environment! 
What does it mean if the light turns on 

while I'm driving? 

If the light comes on and stays on, the OBD system has detected a 

problem. Your vehicle might have a condition that wastes fuel, shortens 

engine life, or causes excessive air pollution. If left unaddressed, these 

conditions could also damage your vehicle and lead to increasingly 

expensive repairs. For example, OBD can identify a loose or missing gas 

cap (which wastes fuel and contributes to smog) or engine misfire 

(which can lead to severe or permanent engine damage). 

What should I do if the light stays on? 

• There is no cause for panic. The vehicle is just telling you to seek 

attention soon. 

• When you reach your destination, make sure the gas cap is not loose 

or missing. Always turn off your engine when refueling. 

• If the light does not go out after a few short trips following gas cap 

replacement or tightening, have your vehicle serviced by a qualified 

repair technician soon! Delaying assistance could lead to more 

expensive damage. 

What does it mean if 

the light is blinking? 

If the light is blinking, a severe engine 

problem such as a catalyst-damaging misfire is occurring and should be addressed 

as soon as possible. You can still drive 

safely, but should minimize your time on 

the road. Try not to drive the vehicle at 

high speed or with excess weight (such as 

towing or carrying heavy equipment). 

What will my technician do when I take my 

vehicle into the shop? 

Ask your repair shop if they employ trained OBD technicians. A modern repair shop or dealership should have an OBD scan tool to diagnose 

the cause of your vehicle's problem. These technicians will have the 

proper tools and will know best how to diagnose your vehicle. 
The technician will connect a small, hand-held scanning device to your 

vehicle's computer (usually through a connector under the dashboard) 

and download information that can pinpoint the problem. The technician can then repair the vehicle based on manufacturer recommendations. OBD actually helps repair technicians do their job more quickly 

and reliably, helping you avoid unnecessary repairs and trips back to the 

shop. 

What should I do if the light goes out 

before I take the vehicle to the shop? 

Usually, nothing. If the problem that caused the light to come on is 

addressed, the OBD computer will turn the light off. 

indication of a faulty OBD system. In fact, the system is doing its job by 

verifying that a problem temporarily existed but has since been corrected; perhaps a loose gas cap was tightened or fouled spark plug was 

cleared. Your vehicle needs no special attention unless the light comes 

on again. 

What else can I do to 

make sure my vehicle 

is running well and to 

minimize its environmental impact? 

Today's vehicles are highly sophisticated and efficient. OBD helps to 

ensure these vehicles are running in top shape, but you still need to 

maintain your vehicle according to the manufacturer's recommended 

schedule. Keep up with routine maintenance and keep an eye out for 

your Check Engine light. Always turn off the engine before refueling 

and always make sure the gas cap is securely tightened. You'll save 

money on fuel and repairs while helping to do your part to protect the 

air you breathe. In addition, driving as little as possible by combining 

trips, carpooling, walking, biking, or using public transit are all things 

you can do to help minimize vehicle pollution. 

This is not an 

For more information on OBD and vehicle inspection and maintenance programs, visit 

<www.epa.gov/otaq/obd.htm> or e-mail <obd@epa.gov>. 

Office of Transportation and Air Quality


EPA420-F-02-016


August 2002


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