What are the chances of a fairly experienced mechanic missing the call on this? Check engine light comes on... Mechanic says O2 sensor is out of spec and replaces it... 3 - 4 weeks later the light is back off and on, then stays on. Gas mileage takes a dive. New mechanic says it's possibly the coolant temp sensor bad and telling the computer the engine temp is cold, hence a consistent richer fuel mixture. After a week or so of the rich mixture, the O2 sensor gives bad readings, showing up in the codes when the check engine light comes on. What are the chances a mechanic just goes for the O2 sensor and doesn't find the coolant sensor problem.... until it all happens again?

I don't see any posts about the coolant temp sensor being a common problem, unlike the numerous ones on the MAF and the harmonic balancer.

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John Myers
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