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Q: Check engine light - O2 sensor circuit + speed sensor circuit...

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My car started occasionally stalling out, usually when slowing down quickly for a turn lane. Last week, the check engine light came on. I assumed I needed a tune-up, so I took it to Autozone to buy spark plugs and get the OBII reading... reading said O2 Sensor, Sensor 1, Bank 1 low voltage. I went to a pull-a-part, found a 2010 Sentra and got an a/f sensor and replaced it. Check engine, still on. Took it to get another reading... Same O2 sensor code PLUS a low voltage code for the speed sensor. I really don't think I did any damage while installing the a/f sensor. Is this likely a problem with the wiring harness? Autozone guy said maybe a mouse was chewing the wires? I can't imagine that. What's my next step?

My car has 118000 miles.
My car has an automatic transmission.

A: Hi there. O2 sensor low voltage can be caus...

Hi there. O2 sensor low voltage can be caused my a number of things. Mass air flow sensor was only one of them. It can be a bad O2 sensor, coolant temperature sensor, or wiring issue.

What should be done is a proper diagnosis for the Check Engine Light. Using a complete scanner rather than just a code reader gives a technician the opportunity to not only read trouble codes, but to read voltages for individual sensors. While a code reader tells you the relevant system that set the Check Engine Light on, but with a number of possible causes, the full scan tool allows checking of each individual cause. Having a proper diagnosis will help you have this repaired correctly without replacing parts that are not faulty.

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