2001 Mazda Protege Check engine warning light

  • 131,000 MILES
Check engine light comes on. Had diagnosed by mechanic, changed Map sensor and check for vacuum leaks. Mechanic said no vacuum leaks. Light still comes on, most of the time. What should I look for?
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Saturday, November 16th, 2013 AT 2:15 AM

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There's over a thousand potential diagnostic fault codes, and many that pertain to any one sensor circuit. Need to know the exact fault code number to know how to start diagnosing the problem. Be aware that fault codes never say to replace parts or that they're defective. They only indicate the circuit or system that needs further diagnosis. When a sensor is referenced in a code, that sensor is actually only bad about half of the time. It is just as likely there is a wiring problem related to that sensor.

Also, there's always a long list of conditions that must be met to set a fault code, and one of them is certain other codes can't already be set. The computers continually run a number of self-tests, and they compare various sensor readings and operating conditions to each other to determine when there's a problem. If there's a code related to a sensor that is used as a reference or for comparison to another sensor, the computer knows it can't rely on those readings so it suspends some of the tests it runs. Once the problem is solved and the fault codes are erased, the tests resume. THAT'S when a totally different problem may be detected for the first time and the Check Engine light may turn on again. You could have a completely different problem. That's why we need to know the code number. We also need to know the symptoms. There's a lot of things to check related to a fault code. Knowing the symptoms can shorten that list of suspects.
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Saturday, November 16th, 2013 AT 3:22 AM

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