Modern vehicles are equipped with an on-board computer diagnostic system (OBDII). This computer constantly monitors and manages the vehicle systems and is constantly adjusting and fine-tuning various parameters according to driving conditions. When the computer detects that any of these parameters falls outside acceptable ranges, the check engine light (CEL) alerts the driver to the problem.
We will connect a diagnostic scanner to the vehicle, and query the on-board system for reported symptoms. Additional diagnostic procedures are used to pinpoint the exact cause of the “trouble” code. Be wary of mechanics that read your code and tell you immediately that you need a major repair.
There are two kinds of CEL alerts. A non-flashing but lit CEL is usually a less severe problem. A non-flashing code will usually cause an increase in emissions and a decrease in fuel economy. A flashing and illuminated CEL means the vehicle senses a critical system error (such as a major cylinder misfire ) and needs immediate attention. Ignoring either type of CEL risks a potential break down and possible damage to other components.
An illuminated check engine light, for any reason, is an automatic fail for Emissions testing. A non-functioning light (doesn’t illuminate at vehicle start-up) is also a fail.
When the check engine light is reset (or if the battery is disconnected) the vehicle resets to a not ready state. This just means that, for emissions testing purposes, the on-board monitors have not had time to check and verify proper function of all the engine management systems. Each manufacturer has their own individual procedures to achieve readiness. Here are a few examples gathered on-line:
It may be possible to use one of these specific procedures to get your car “ready” faster. However, in most cases, the easiest way is to simply drive your vehicle normally for ~100 miles, with a mix of city and highway driving. For most drivers, and most vehicles, we have found that ~100 miles or normal driving will set all the necessary readiness flags.
The check engine light is just one of many diagnostic indicators on a modern vehicle. We diagnose, troubleshoot, repair, and eliminate all of these trouble indicators.