OBD2 codes tests

obd2 codesPerforming OBD2 codes test needs serious analysis on what is the root cause of the fault code. Relying on the description of the fault alone is an expensive method of repair when it does not address the problem properly. One example is when analyzing OBD2 P0420 codes which detects CAT (catalytic converter) efficiency. Most often, most vehicle owners and a few mechanics will see this CAT code and go ahead and replace it along with their respective oxygen sensors. They will likely use an aftermarket parts to cut cost. This is a serious mistake since a lot of these aftermarket parts don't use stringent components use by the vehicle manufacturers. The end result is very much a disaster since after doing those things, those same fault codes re-appear.

As reported by various garages, here are some serious OBD2 Codes testing mistakes:

1.) One garage changed all of the CAT and downstream sensors but failed to find a previous garage using silicone adhesive which corrupted the the probe tips of the oxygen sensors. This lead to a faulty code reading. The customer suffered because that silicone should had been checked first instead of replacing the exhaust parts right away. If oxygen sensor obd2 codes testing were monitored by comparing the upstream and downstream voltage switching, this problem could have been avoided.

2.) An exhaust leak in the exhaust system can affect the CAT and oxygen sensor readings. A visual inspection should be done first if a fault CAT or oxygen sensor code is found. It saves time and will always earn customer respects if the problem is fixed by sealing the exhaust leak.

3.) Some great difficulty are encountered when using generic OBD2 scanners. When analyzing CAT problem, a good look at the scanner monitoring of the short and long fuel trims. This will help verify if the engine computer is in full control which can tested by inducing a vacuum leak or rich fuel condition which will be reported by the live datastream monitor of the scanner. Example is when the fuel trim has changed after the introduction of the vacuum leak, at least it shows that the engine computer controlling the fuel system.


A fuel lean condition can be manually induced if one of the vacuum hose cover is removed. It should make the fuel trim reading of the scanner response by making the fuel mixture from rich to lean. Most generic scanners should have these features before buying them.

The same effect can be seen if a bottled propane gas is sprayed in the throat of the engine air filter opening when the engine is running. If the scanner is hooked up while doing this, the fuel trim will change from lean to rich fuel mixture.

4.)Still a few garages are now finding that an upgraded computer data programming is required to fix the problem instead of the replacing the exhaust emission parts. The CAT alone can cost about a thousand dollars even using aftermarket parts.

Please go over these drop down menus below for testing different types of OBD2 codes for different makes of vehicles. A brief OBD2 test is included to give any type of fault OBD2 codes, the proper definition and testing of the OBD2 fault codes. Coverage of testing these OBD2 codes are for vehicles models made between 2006 to 2008.

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