First of all, understand there are over 2,000 problems the Engine Computer can detect. It will set a diagnostic fault code for each of them, but only about half of those problems relate to something that could adversely affect emissions. Those are the codes that turn on the Check Engine light.
For each of those diagnostic fault codes, there is always a long list of conditions that must be met for that code to be set, and one of those conditions is that certain other codes cannot already be set. When a sensor circuit, for example, has been detected as having a problem, any other circuit that uses its information for comparison cannot be tested because the computer knows it cannot rely on the information from the circuit with the defect. Some of the self-tests will be suspended. That means while you are driving and ignoring the Check Engine light, a minor problem could go undetected and could turn into a very expensive one. Also, another problem could develop and you will never know it because the warning light is already on. Some people say they know which fault code has been set, and it is not serious, so they think it is okay to keep driving with the Check Engine light on. That logic says it is okay to keep racing after the ambulance has left the race track. "No serious crash can occur because the ambulance is gone". Obviously that does not make sense. Neither does ignoring the Check Engine light because you know which fault code has been set.
Of those 1,000 plus fault codes related to emissions concerns, only about a dozen refer to your oxygen sensors, and they mean very different things. No fault code ever says to replace parts. They only indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition. When a part is referenced in a fault code, that part is the cause of the code only about half of the time. First you have to rule out wiring and connector terminal problems, and mechanical problems associated with that sensor.
The place to start is by having the diagnostic fault codes read and recorded. The people at many auto parts stores will do that for you for free. Once the code numbers are known, we can figure out where to start the diagnosis.
Monday, January 9th, 2017 AT 2:11 PM