|04-11-2012, 06:01 AM||#1|
Join Date: Mar 2012
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what do you do now that you have a code?
When you plug a code reader or scan tool into the diagnostic connector, the tool will display any trouble codes that are in the powertrain control module (PCM) memory. There may be only one code, or there may be multiple codes. Basic code readers may only display a number, which you then have to look up in a reference book or online to find out what it means. Better scan tools display the trouble code number and a short definition of what the trouble code means.
Write down any codes and definitions that are displayed for future reference.
So what do you do now that you have a code? It depends on the code. A trouble code by itself does not tell you what part needs to be replaced. It only indicates the circuit or component where the fault occurred (oxygen sensor, for example), or the nature of the fault (misfire, for example).
Further diagnosis is usually necessary to isolate the fault and figure out what is causing the problem and which part (if any) needs to be replaced. This often requires following a lengthy diagnostic chart and step-by-step checks to rule out various possibilities. This kind of information can be found in the vehicle service literature or on Alldata.
For example, let's say your Check Engine Light is on and you find a trouble code for one of the oxygen sensors (code P0130). The code might indicate a bad sensor, or it might indicate a loose connector or wiring problem. You should check the wiring first before replacing the sensor.
Harder to diagnose are misfire codes. OBD II can detect misfires in individual cylinders as well as random misfires. If it generates a misfire code for a single cylinder (say P0301 for the #1 cylinder), it only tells you the cylinder is misfiring, not why the cylinder is misfiring. The underlying cause could be a bad spark plug, a bad plug wire, a weak coil on a distributorless ignition system (DIS) or coil-on-plug (COP) system, a dirty or dead fuel injector, or a compression problem (bad valve, leaky head gasket, rounded cam lobe, etc.). As you can see, there are multiple possibilities so it takes some diagnostic expertise to isolate the fault before any parts can be replaced. Good code reader is very inportant.
A "random misfire code" (P0300) is even harder to diagnose because there can be numerous causes. A random misfire usually means the air/fuel mixture is running lean. But the cause might be anything from a hard-to-find vacuum leak to dirty injectors, low fuel pressure, a weak ignition coil(2), bad plug wires or compression problems.
For a detailed look at all the operating parameters that can set trouble codes, Click Here to view a PDF file on GM 4.6L diagnostic parameters.
The best advice in situations like this is to take your car to a repair facility that has the proper tools and expertise to accurately diagnose the fault.
|04-23-2012, 12:36 PM||#3|
Join Date: Oct 2008
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