Briefly stated, it is feasible to identify a vehicle’s problem even if the check engine light does not illuminate on the dash. A competent repair would begin by retrieving any error codes that may have been stored in the computer of your car.

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When an Engine Fault Code is detected in the United States, the CEL will illuminate. Most of them are required by Federal Emissions Regulations, and the remaining faults are usually warnings about serious engine damage or stalling/losing of power, which will illuminate the CEL.

There are some codes that do not result in a CEL being displayed. These are typically diagnostic codes that are sent to dealerships or other repair shops to alert them to a specific drive train fault, but they do not affect the vehicle’s performance. Occasionally, in some vehicles, a performance or replacement ECM will result in an internal code indicating that it is not the original ECM for the vehicle. However, there is no CEL.

Some codes are unrelated to the engine or emissions systems and do not result in the illumination of the check engine light.

There are also instances in which there is no check engine light, yet there are codes. For example, any fault that impacts the emissions system will cause the check engine light to illuminate automatically. The computer will then switch off the check engine light and save the code as an HISTORY CODE for subsequent use if the problem does not recur.