Friday, December 14, 2012

What is a "Check Engine Light" and what to do if it comes on

The Check Engine Light

A. What is the Check Engine Light?
The “Check Engine Light”  
was originally named the “Malfunction Indicator Light.”
Some vehicles may have the words “Service Engine Soon” instead of the “Check Engine Light.”
Self-Check- Once the ignition key is turned to the “on” position (engine off), all of the instrument panel lights should come on, including the “Check Engine Light.”  This checks the bulb and diagnosis circuitry operation.  The Check Engine Light should go out (turn off) after about 10 seconds or less.  Once the vehicle starts, all of the lights should turn off.

B. Purpose
The purpose of the “Check Engine Light” is to alert the driver that an emission control device on the vehicle is not operating correctly.  If the malfunction is serious, that is, if the engine is misfiring for example, the light may flash, otherwise it will remain lit (on).

C. History
The California Air Resources Board (CARB) required all new vehicles to have an On-board Diagnosis system (OBDII) installed to monitor the proper operation of emission control components.  This started with the 1996 model year and adopted by the US Environmental Protection Agency to apply to all new vehicles sold in the US.
There were specific requirements to meet OBDII standards, some were:
·         A standardized connector located under the dashboard on the driver’s side of the vehicle within 2 feet of the steering wheel (unless a waiver was granted.)
·          Vehicle manufacturers provide standardized Diagnostic Trouble Codes (DTC) indicating a malfunction.
·         Devices to control emissions is monitored and alert the driver if a malfunction is detected by turning on a Malfunction Indicator Light (MIL) that is also known as a “Check Engine Light.”
·         If there is a malfunction, the OBD II system has the capability to store the fault into the PCM (engine computer) memory for retrieval by a scan (diagnostic) tool.
·         After a certain number of start cycles, if the fault does not continue, the check engine light will turn off.

D.  What to do if it comes on
·         If the check engine light is flashing, this indicates a failure of an emission control component or engine misfire.  If the vehicle drive ability is normal, do not panic, just drive home and have it checked out as soon as possible.
·         If you continue to drive with a flashing check engine light, the worst-case scenario is you may have to replace your exhaust catalytic converter, which can cost over $1,000.  If you converter needs to be replaced and you cannot afford a new one, buy a used one from the automotive junk (salvage) yard.
·         If the check engine light is on steady and the vehicle is running normally, do not panic, just drive home and have it checked out as soon as possible. 
·         If the vehicle is not driving normally but if it can be driven safely, drive it home and have it checked out as soon as possible.
·         If the vehicle is not driving normally and cannot be driven, home safely, have it repaired on location by a mobile mechanic (locate on internet or yellow pages) or have it transported to a repair facility, preferably on a flatbed transport truck.

E.  Conclusion
The Check Engine Light is not a diagnostic light to reveal internal engine damage but rather to reveal faulty components that will effect emissions. 
Therefore, do not panic when the “Check Engine Light” comes on, it is only alerting you to this reality.  Three different vehicle scenarios can occur when the check engine light comes on:

1.    The vehicle shuts off:  Transport it to a repair facility.
2.    The vehicle runs rough, has low power or runs bad: Drive the vehicle safely to the repair facility or have it transported
3.    The vehicle drives normal: This is a less serious condition and a matter of a sensor malfunctioning or something preventing a normal operating condition.  Identify and correct the cause to prevent damage to the catalytic converter.
For Do-It-Yourselfers or willing to be DIY’ers, you can purchase an easy to use check engine light reader with full instructions and systematic support from this location

Next topic:  Is buying a certified used vehicle worth it?

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