Car Techniks
Better Service For Less. Since 1981 Thursday, April 27, 2017
What can be done to prevent my check engine light from coming on ...

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  Why my Check Engine light (MIL) comes on?  
CheckLight All modern vehicles have a computer or the ECM (Electronic Control Module) that controls the engine operation. The main purpose of this is to keep the engine running at top efficiency with the lowest possible emissions.

With today's strictest emission regulations it's not very easy to achieve - the engine needs to be constantly and precisely adjusted according to various conditions such as speed, load, engine temperature, gasoline quality, ambient air temperature, road conditions, etc.
Today's cars have much more electronics than in early days - there is a large number of various sensors and other electronic devices that help the engine computer or ECM to monitor all vehicle emission-related systems.

When the computer senses that there is a problem with any emission-related system or component, it stores the trouble code(s) in the memory and lights up the "Check Engine" or "Service Engine Soon" light to tell you that there is a problem and your car needs to be looked at. The technician at the dealership or a garage then will hook up the scanner to the car computer and retrieve the stored code(s). Then he (she) will look it up in the service manual provided by a car manufacturer. The service manual contains the list of possible codes (about few hundreds) and describes what each code means and what needs to be tested. The code itself doesn't tell exactly what component is defective - it only says what engine parameter is out of normal range. The technician will have to perform further testing to pinpoint defective part.

How this works?

Let's look deeper how all this works:
There is a number of sensors that provide the ECM with all necessary inputs such as the engine temperature, ambient temperature, vehicle speed, load, etc. According to these inputs, the ECM makes initial adjustments adding or subtracting fuel, advancing or retarding the ignition timing, increasing or decreasing idle speed, etc.

There is a primary (upstream) oxygen sensor installed in the exhaust before catalytic converter that monitors the quality of combustion in the cylinders. Based on the feedback from this oxygen sensor the ECM makes further adjustments to the air-fuel mixture to further reduce emissions. There is another, secondary (downstream) oxygen sensor installed after catalytic converter in the exhaust that monitors catalytic converter's efficiency.

Besides, there are few additional emission control related vehicle systems. For example, there is an Evaporative system (EVAP), designed to prevent gasoline vapors from the gas tank from being released into the atmosphere. It also contains a number of sensors and actuators controlled by the ECM. The ECM has self-diagnostic capability and constantly tests operation of all sensors and components. When any of the sensor signals is missing or out of normal range, the ECM sets a fault and illuminates the "Check Engine" or "Service Engine Soon" light also called MIL (Malfunction Indication Light) storing the corresponding Diagnostic Trouble Code (DTC) in the ECM memory.

The same will happen if a mechanical component of controlled system fails. For example, if the EGR valve fails, this will also cause the "check engine" light to come on. Even a loose gas cap will cause the "check engine" to come on - the ECM constantly checks if the gas tank is sealed properly. To sum up, the "Check Engine" or "Service Engine Soon" light comes on when there is a problem with any emission-related component or system. The stored trouble code can be retrieved with the special scan tool by our technician. The code itself does not tell exactly which part to replace, it only gives a direction where to look for - our technician has to perform certain tests specific for each code to find the exact cause of the problem.

Q: What to do if my "Check Engine" light is on?
A: The simplest way is to visit our car care center for proper diagnostic. We have all the equipment and information needed to correct the problem. The problem might be even covered by the manufacturers warranty and possibly repaired free of charge.

Q: Is it safe to drive if my "Check Engine" light is on?

A: It really depends what code is stored and what caused it. In worst cases driving with check engine light may cause more damage to the vehicle. A car may even stall while driving. If your check engine light came on, I'd certainly recommend to visit our shop as soon as possible, just to be on a safe side. If the Check Engine light is flashing, this means that the engine computer (ECM) has detected that your engine is misfiring, which could damage your catalytic converter. Have your vehicle inspected as soon as possible.

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