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When the Check Engine light comes on, it means the truck has sensed a problem. So, obviously you should try to find out what the problem is.

Although there may not be any symptoms, you can still damage your car by continuing to drive without fixing the problem.

When the Service Engine Soon or Check Engine light comes on, you have a few options. You can take your car or truck to the dealer.

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The internal combustion engine is an engine in which the combustion of a fuel (generally, fossil fuel) occurs with an oxidizer (usually air) in a combustion chamber. In an internal combustion engine the expansion of the high temperature and pressure gases, which are produced by the combustion, directly applies force to a movable component of the engine, such as the pistons or turbine blades and by moving it over a distance, generate useful mechanical energy. The term internal combustion engine usually refers to an engine in which combustion is intermittent, such as the more familiar four-stroke and two-stroke piston engines, along with variants, such as the Wankel rotary engine. A second class of internal combustion engines use continuous combustion: gas turbines, jet engines and most rocket engines, each of which are internal combustion engines on the same principle as previously described. The internal combustion engine (or ICE) is quite different from external combustion engines, such as steam or Stirling engines, in which the energy is delivered to a working fluid not consisting of, mixed with, or contaminated by combustion products. Working fluids can be air, hot water, pressurized water or even liquid sodium, heated in some kind of boiler. A large number of different designs for ICEs have been developed and built, with a variety of different strengths and weaknesses. Powered by an energy-dense fuel (which is very frequently petrol, a liquid derived from fossil fuels), the ICE delivers an excellent power-to-weight ratio with few disadvantages. While there have been and still are many stationary applications, the real strength of internal combustion engines is in mobile applications and they dominate as a power supply for cars, aircraft, and boats, from the smallest to the largest. Only for hand-held power tools do they share part of the market with battery powered devices.
A malfunction indicator lamp (MIL), commonly referred to as the "Check Engine Light" is an indicator of malfunction of the computerized engine management system. It is found on the instrument console of most automobiles. When illuminated, it is typically either an amber or red color. On vehicles equipped with OBD-II, the light has two stages: steady (indicating a minor fault such as a loose gas cap or failing oxygen sensor) and flashing (indicating a severe fault, that will eventually destroy the catalytic converter, such as a misfire). When the MIL is lit, the engine control unit stores a fault code related to the malfunction, which can be retrieved with a scan tool and used for further diagnosis. The malfunction indicator lamp is usually labeled with the text check engine, service engine soon, check engine soon, or a picture of an engine. The MIL appeared in the early 80s along with computerized engine controls. Even the earliest systems, such as GM's CCC (Computer Command Carburetor) system had self diagnosis functionality. When the computer detected a fault, it illuminated the MIL. Up until OBDII, on most cars the MIL could output codes, when two pins on the ALDL are jumped, the light would flash the codes, for instance (blink) (pause) (blink) (blink) for code 12. Some manufacturers retained this feature even after OBDII, such as Honda.
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some causes Higher amounts of methanol/ethanol (or other additives) than the engine can handle efficiently may also trigger the malfunction indicator lamp (see E85). These burn differently from gasoline, and the EFI system may mistakenly interpret the oxygen sensor's readings as being incorrect. Oxygenated gasoline (ie. in California) may also cause this problem ("too lean" or "oxygen sensor" failure) in early EFI systems. Engines encompass a number of systems that work together to provide excellent performance under normal circumstances. The vast majority of engines on the road today are powered by electronic fuel injection (EFI). The EFI system employs a number of valves and sensors to ensure the correct amount of air and fuel are fed to the piston chambers to create the right combustion mixture. Timing of the spark is also controlled electronically. If any one of these systems fails, this can trigger the check engine light. Another event that is often responsible for tripping the check engine light is a vacuum leak. In this case a hose or manifold might be loose or cracked. A visual inspection can help, but in some cases a vacuum leak can be very difficult to locate. Some repair shops offer a smoke test for about $60 US Dollars. A smoke generator made for this purpose is used to fill the air intake system and hoses are closely monitored for escaping smoke. Other vacuum leaks that can trip the check engine light include a sticky exhaust gas recirculation (EGR) valve, or more seriously, a blown head gasket. Pinched or deteriorated fuel injector o-rings might also be the culprit. Dirty fuel injectors or a faulty oxygen (O2) sensor might also be to blame. Because there are so many possible reasons for the check engine light to come on, pulling the codes for the event can be helpful when the problem is not immediately evident. Even if the check engine light is only on a short time, a code will be stored in the ECU for later retrieval. US vehicles manufactured prior to 1996 feature a diagnostic module in the engine compartment by the main fuse box. Often a label is affixed to the underside of the hood explaining which terminals to access. Using a simple metal tool (even a paper clip) to connect the two terminals will cause the check engine light to flash in the dash when the key is in the accessory position. By reading the number of flashes one can determine which code was set. Manufacturer’s code guides, available online, will reveal which system(s) tripped the check engine light. US vehicles manufactured after 1996 are required to feature a Molex-style connector under the dash, normally by the driver’s side. These connectors can interface with a dongle-to-USB cable to plug into a laptop running auto diagnostic software. The software not only reveals the code(s), but corresponding possible cause(s), and can perform many other diagnostic functions. A check engine light doesn’t always mean a big problem or an expensive repair is ahead. However, driving a car with the check engine light on could mean that you are doing further damage to the engine, depending on the problem. It’s always best to get the vehicle checked at your earliest convenience.	probable solutions TURNING THE CHECK ENGINE LIGHT OFF The OBD II Check Engine light will generally remain on as long as a fault persists. If an intermittent fault does not reoccur after three consecutive trips, the MIL lamp will go out, but the trouble code will remain in memory. If the fault does not reoccur for for 40 to 50 trips, the code will be erased. The only safe way to clear fault codes and turn of the Check Engine Light is to use a scan tool or code reader. Most of these tools have a button or menu choice that says "Clear Codes?" When you press the button or choose the option, it wipes the code from the PCM's memory. This will take you back to ground zero. ADVICE: Write down any codes you have found BEFORE you erase them! Don't think you'll remember them because in a few days you probably won't. If the Check Engine Light comes back on again (which is usually does if there is a hard fault in the system), you can check the codes again to see if they are the same ones as before. This would confirm the fact that you have an emissions problem, and that further diagnosis and repairs are probably necessary. NOTE: Many emission faults that sets codes won't have any noticeable effect on the way your car starts, drives or behaves. So you may be tempted to just ignore them. That's up to you. But if you live in an area that requires emissions testing, your vehicle will NOT pass an emissions test if the Check Engine Light is on. On older pre-OBD II vehicles (1995 and back), trouble codes can also be cleared from the PCM's memory by disconnecting the battery. Unhooking the battery ground cable for 10 seconds, then reconnecting it will "reset" the computer. But it will also wipe all of the other learned settings from the PCM's memory, too. That means your engine may not idle smoothly or feel quite right for some time until the PCM relearns what it needs to know. Same for the transmission controller. You will also lose the channel presets on the radio, and any other electronic settings (memory seats, mirrors, etc.). That's why a code reader or scan tool should be used to clear the codes only. WARNING: On many 1996 and newer OBD II cars, pulling the PCM fuse or disconnecting the battery may NOT clear the codes, and may cause a loss of important information the PCM needs to function correctly. This is certainly true on 2004 and newer vehicles with Controller Area Network (CAN) electrical systems. DO NOT DISCONNECT THE BATTERY ON THESE VEHICLES! On some vehicles, loss of power to the PCM may cause it to forget transmission settings, climate control functions and other essential data. This, in turn, may require an expensive trip to the new car dealer so they can use a factory scan tool to reset or reprogram the information that was lost.