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Fixing Your "Check Engine" Light
By Pat Goss
Printable version
Degree of DifficultyModerate
Moderate
Estimated Time60 minutes
60 minutes
After verifying the condition of the battery and alternator, perform a thorough visual inspection of all hoses and wires. You’re looking for frayed or oil soaked wires and vacuum hoses, and anything else that looks suspicious.
Checking Hoses
The next step requires critical test equipment you probably don’t have. Have the engine connected to an engine analyzer, which must not be confused with a computer scanner. An engine analyzer uses two primary testers to determine that all baseline parts are functioning properly. Baseline parts control fuel delivery and produce high voltage to fire the spark plugs. The two pieces of equipment are an oscilloscope to look at electricity as it moves through parts, and an exhaust gas analyzer to measure tailpipe emissions for diagnostic purposes. These are extremely important tests because there are many failures in baseline systems that cause “Check Engine” lights and codes.
Connect the Engine to an Engine Analyzer
Finally, it’s time to retrieve codes, which requires an inexpensive code reader from an auto parts store or online source. To fix code-related problems you’ll need factory-test information from a source like Alldata or a factory service manual. You’ll also need a computer-safe test light and a Digital Volt Ohm Meter (DVOM).
 
Just remember, codes do not directly tell what’s wrong, so you have to test to find the real culprit. This is where the true meaning of codes comes into play. The only thing a code really tells you is what test to perform to isolate the true problem.
 
Each numerical code has a matching-numbered test procedure. Following that test will direct you to the problem, providing you follow the rules. Each step of each test must be performed in absolute sequence. Skipping steps or performing steps out of sequence could make the entire test worthless. Tests may also give you voltage, resistance, temperature, or time specifications, which are exact values. Close doesn’t count.
 
By following proper test procedures, you’ll get rid of the pesky “Check Engine” light without breaking the bank. If you can use simple test equipment and read and follow directions, you can do “Check Engine” light repair just like the pros.
Pat Goss is the co-host of PBS’ “MotorWeek;” the host of “Goss’ Garage,” a radio talk show on WJFK-AM in Washington, DC; an automotive columnist for the Washington Post; and the owner of Pat Goss Car World, an auto-body and repair shop in Seabrook, Maryland.
 
© Copyright 2005 Pat Goss, all rights reserved.
Article Author Pat Goss
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