If the indicator comes on while driving, it means one of the engine’s emissions control systems may have a problem. Even though you may feel no difference in your vehicle’s performance, it can reduce your fuel economy and cause increased emissions. Continued operation may cause serious damage.

If you have recently refueled your vehicle, the indicator coming on could be due to a loose or missing fuel fill cap. Tighten the cap until it clicks at least once. Tightening the cap will not turn the indicator off immediately; it takes several days of normal driving.

If the indicator comes on repeatedly, even though it may turn off as you continue driving, have your vehicle checked by your dealer as soon as possible.

If you keep driving with the malf unction indicator lamp on, you can damage your vehicle’s emissions controls and the engine. Those repairs may not be covered by your vehicle’s warranties.

If your vehicle has an automatic transmission, the malfunction indicator lamp may also come on with the ‘‘D’’ indicator.

Readiness Codes

Your vehicle has certain ‘‘readiness codes’’ that are part of the on-board diagnostics for the emissions systems. In some states, part of the emissions testing is to make sure these codes are set. If they are not set, the test cannot be completed.

If the battery in your vehicle has been disconnected or gone dead, these codesmay be erased. It can take several days of driving under various conditions to set the codes again.

To check if they are set, turn the ignition switch to the ON (II) position, without starting the engine.

The malfunction indicator lamp will come on for 20 seconds. If it then goes off, the readiness codes are set.

If it blinks five times, the readiness codes are not set. If possible, do not take your vehicle for an emissions test until the readiness codes are set.

Refer to Emissions Testing for more information.