It can be scary when you are driving and your "service engine soon" (SES) light comes on. There are multiple issues that can cause the light to come on. While some may be simple, others may be a big problem. There is no way to tell for sure at the moment what is wrong unless your Nissan is also acting funny.
Check your gas cap. This is a very common issue that triggers an SES light in Nissans. If the gas cap isn't sealed properly or if it was opened while the truck was running, the light will come on. Replace the cap if necessary. If you took the cap off when your engine was running, you can reset the SES light by disconnecting and reconnecting your battery cable.
Diagnose the problem with your vehicle by using a universal code reader. This machine reads the error code your truck is giving, and tells you the corresponding problem for that code. Taking it to a mechanic is always an option, but this usually costs money. Take your truck to an auto parts chain and have your SES diagnostic done for free.
Use the universal code reader by putting your truck into its diagnostic test mode. Turn your ignition on, but do not crank the engine. Depress and fully release the gas pedal five times quickly within five seconds. Wait seven seconds and push the gas pedal down and hold it for 10 seconds. This should cause the SES light to start blinking. Let off the gas pedal. The number of blinks (for example, one blink equals "1," five blinks equals "5," ten blinks equals "0") tells you what error code you have. You can then look it up. After you have your results, hold the gas pedal down for 10 more seconds to erase the memory and reset your SES light.
