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May

Check Engine Light – Code Readers

Posted by: Jeff Williams | Comments (5)

If you have ever seen one of these pop up on your dash then I know that for most of you the thought of catastrophic engine failure along with a hefty repair bill has entered you mind.

Well I am here to shed some light on this subject and give you some clues as to what this light means and it is trying to tell you .

If you see a "check engine" or a "service engine soon" light in your instrument cluster; your car has stored a diagnostic trouble code. Which means the computer system on your vehicle has detected a problem within various systems it controls. Your car has many different sensors that monitor the various vehicle systems.

If the trouble code light has been illuminated then your vehicle enters into a "limp mode" . This means it is running on a program that causes poor mileage and increased emissions.

To find out what trouble code or codes were stored then you must use a code reader or Scan Tool . Most scan tools will tell you all of the codes that are stored in the PCM and most of the time in the order they were stored.

Now code readers come in a large variety of shapes and sizes but I would recommend the Actron for quick easy scans at a very low price but remember that you get what you pay for and in this case you will have to look the code up to find out its definition.

Now if you plan on working on your own vehicle quite a bit then I highly recommend paying for a subscription to www.alldata.com. Its one of the best web sites for the do it your selfers and they supply a lot of info that you cant get any where else. It will cost you about $ 26.00 dollars for your first vehicle and $ 16.00 for every vehicle after that and the subscription lasts for one year. Its well worth it and they give you all the TSBs or Technical Service Bulletins, Which are very helpful in diagnosing your problem.

Now for the rest of you that prefer something a little more sophisticated, there are scan tools that are OEM specific that have the manufactures programs installed in them, but they can cost up wards of 5 to 8 thousand dollars, not including attachments.

I personally like to use the OTC Genysis Scan tool for pulling codes . Its easy to use and upgrades wont cost a fortune.

Now most scan tools are user friendly and all 1996 and newer vehicles utilize a "D" style plug-in connector that connects to the code reader. On most vehicles the connector is located at the driver's compartment. Once the code reader is plugged in you can retrieve trouble codes the engine computer has stored in its memory. These codes are the same codes the dealer and repair shops use to diagnose and repair your vehicle, as well as clearing the trouble codes from the computers memory.

Remember that an engine trouble code reader is an easy tool to use and is a worth while investment for future repairs.

First locate your vehicle's computer connector (ALDL) or Data Link Connector , most are on the lower driver's side. In some vehicles you might need to look around a little, on the passenger's side, and around the center console under a plastic cover. For more information, check your owner's manual.

Connect your code reader to the under dash Data Link connector. The code reader will automatically turn on and prompt you to the next step for code retrieval. Once the code has been identified look up the identification on the trouble code chart supplied with your code reader.

After repair has been made, clear the trouble codes and re-check system. After codes have been cleared the computer system is ready for internal testing, this means that while the car or truck is in operation and the on board computer is performing tests. These tests are called "monitors" and most cars have between 4 and 8 monitor systems. The computer goes through its testing procedure in about 40 to 60 miles.

Most on Board Computers are called ECMs ( Electronic Control Modules ) or on the 1996 and newer models they are called PCMs ( Powertrain Control Modules ) and they usually look like this. The job of the ECM or PCM is to monitor the input and output signals produced by various sensors in the system. The ECM or PCM then adjusts the system as necessary.

Sensors can include: oxygen sensor, coolant sensor, mass air flow sensor, air intake sensor, crankshaft angle sensor, throttle position sensor, camshaft angle sensor and knock sensor. The ECM operating program consists of information cells. These cells hold the code for proper engine operation, if information is outside the cell parameters, a MIL (malfunction indicator lamp) or "check engine light" is illuminated on the dash.

Once a "check engine" or a "service engine soon" light in your dash has illuminated, the ECM has stored at least one diagnostic trouble code. This means the computer system on your vehicle has detected a problem with the various systems it controls. Your car or truck has many different sensors that monitor the various vehicle systems.

If the trouble code light has been illuminated your vehicle enters into "limp mode" this means it is running on a special program that causes poor mileage.Trust me if you are running on "limp mode" it will feel like your car is about to stall.

The ECM outputs a 5 volt reference to most sensors to drive the monitoring circuits. The ECM also controls the radiator cooling fan, air pump controls, fuel pump, EVAP system and more depending on the vehicle.

Manufacturers have different trouble codes for each vehicle and some can be very generic. Check with a good after market repair manual if your code reader cannot give you the definition of your code so you can know where to start looking.

And remember that a code definition doesnt mean that a specific sensor is bad. Check it out before replacing it or you could be throwing your money away.

Well I hope this has answered a few questions about that mysterious " Check Engine Light " and if you have any more questions, I would like to hear from you. Just leave a comment by clicking on the contact us tab at the top of the page and I will try to answer it for you as soon as possible.

Until next time , this is ASE Master Mechanic Jeff Williams saying " Thanks for Stopping By " and if this web site has been helpful to you then please help us keep it running by clicking on the coffee cup icon below. Your support is greatly appreciated. Jeff

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