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Someone told me it could be a minor leak somewhere but the check engine light does indicate the above on Mazda 626,year 2000. Could the code be misleading?

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what's the code? What engine size? –  Larry Jul 28 '11 at 5:58
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Is there more than one O2 sensor, have you replaced the correct one? Does the code indicate that the O2 sensor is giving invalid readings or poor readings? It could be another part that is not working correctly and the O2 sensor is detecting it. –  jzd Jul 28 '11 at 11:14
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Please edit your question to include more information about what symptoms the car is having, what you have replaced and checked already. –  Larry Jul 28 '11 at 16:40
    
The car runs great, no problem at all and it is even good on gas, just the check engine light got on when I filled the gas. I found this artile useful though here is the link –  Dave Jul 28 '11 at 19:38
    
Btw my question is really simple. Can the code be misleading? if yes what could cause it. Of course a mechanic would know :) –  Dave Jul 28 '11 at 19:41
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2 Answers 2

Certainly can be misleading. It's just saying that the values from the sensor aren't matching up with what the computer expects to be happening as it makes adjustments. Sensor could be bad, wiring could be bad, another sensor could be bad that makes the computer think that the O2 sensor should be doing something different, could be an exhaust leak, possibly a vacuum leak, potentially even a bad fuel injector, etc.

MIL codes are not definitive. They just tell you what the ECU has detected. It's the mechanic's job to investigate that to confirm (or deny) and then repair as needed.

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up vote 0 down vote accepted

The check engine light was on and it indicated 3 problems.

EGR Valve O2 Sensor Leak somewhere

I check it in two stores + my mechanic and the codes were consistent in all places. We though the problem is probably with electrical wiring since almost all causes show in AutoZone tips showed one reason as poor electrical connection.

A few days ago my battery died and my car will not start even if i drove it a couple of miles with a jump start. Got a new battery and check engine light disappear. All three codes clear for now but I will go to inspection and will re-edit this answer if my emission fails.

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Please ask your question about the downvotes on Motor Vehicle Maintenance & Repair Meta (meta.mechanics.stackexchange.com/questions/ask) –  Larry Aug 6 '11 at 18:02
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