O2 sensors very low readings - Engine Troubleshooting


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O2 sensors very low readings

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cipi64
New User

Jul 11, 2012, 10:47 AM

Post #1 of 4 (1785 views)

O2 sensors very low readings	Sign In

2002 Mazda MPV ES, 3L, 95K

Engine idles rough, but no significant loss of power during driving (though there is some hesitation accelerating).

All 4 HO2 sensors read very low voltages, never more than 0.2V and pretty steady (no oscillation). There are two banks (one for each side of the V6 motor), one upstream of cat and the other one downstream.
There is noticeable exhaust odor near the front of the car, one mechanic sugested that the front exhaust manifold leaks another pointed at two flexible pipes (under the car). Before i put a couple of thousands in exhaust parts i am trying to understand how is it that these readings can be so low on both banks.

Thanks for your feedback.

O2 voltage chart:

http://cdn.2carpros.com/...large.jpg?1342029044

(This post was edited by cipi64 on Jul 11, 2012, 11:41 AM)

Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Jul 11, 2012, 3:05 PM

Post #2 of 4 (1737 views)

Re: O2 sensors very low readings	Sign In

What codes is it setting?

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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.

cipi64
New User

Jul 11, 2012, 3:52 PM

Post #3 of 4 (1727 views)

Re: O2 sensors very low readings	Sign In

I originally had P0134, P0131 and P0151.
I noticed on page 01-02A-68 of the workshop manual that P0131 and P0151 ought to be ignored until P0134 is fixed. Because i disconected the battery as part of other troubleshooting steps all these codes got erased and i haven't seen them back yet.

thanks for looking

Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Jul 11, 2012, 4:20 PM

Post #4 of 4 (1721 views)

Re: O2 sensors very low readings	Sign In

Those are all lean codes which agrees with your findings. The first thing I would look for are vacuum leaks or air leaks in the intake snorkel.

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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.

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