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Diagnostic Trouble Codes
When your vehicles computer detects a fault it will alert you by setting a trouble
code and possibly lighting your check engine light.
Trouble codes can be classified as pending or current. Usually if a pending code
has been set it is because a fault was detected once. Pending codes usually mature
into current codes.
Diagnostic Codes may also leave a Freeze Frame which may leave clues as to the conditions
at the time of the setting of the code. This can be useful in trying to duplicate
the problem.
Here is a screenshot showing Diagnostic Trouble Codes and Freeze Frame from a Ford
E150 van. It shows that the vehicles computer was not reading enough EGR flow. This
could be caused by two things.
1. Either the EGR was actually not flowing due to a plugged passage, bad valve,
ect.
2. The sensor that reads the opening of the valve did not correctly relay
the correct flow to the engines PCM Module.
It is very common that the sensor is the culprit as it was here.
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