Engine Light Back On, Need Advice
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Joined: Jun 2018
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From: Chicago Illinois
Engine Light Back On, Need Advice
Okay so about two weeks ago my engine light came on. P0131. Bank 1 sensor 1 O2 sensor, low voltage. So I replaced the sensor. Today, codes P0131 and P0151 (both upstream O2 sensors low voltage), were thrown when my engine light came back on. What could be causing this? Car seems to be running fine. Someone told me it could be a dirty Mass Air Flow sensor, which could be throwing off the readings of the upstream O2 sensors? That's odd that they both went off at the same time, especially after I just replaced the one. Another thing I've heard is a vacuum leak.
Not sure if this matters, but the engine light came on under the exact same conditions both times. After about an hour of spirited driving with fairly regular wide open throttle pulls.
What do you guys think?
Not sure if this matters, but the engine light came on under the exact same conditions both times. After about an hour of spirited driving with fairly regular wide open throttle pulls.
What do you guys think?
Last edited by Evan97; Aug 25, 2019 at 10:48 PM.
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Joined: Sep 2013
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From: Cape Coral, Florida
Well first off just because a DTC says “O2 sensor” it’s not always a sensor issue !!...in your case since it’s setting BOTH up streams O2’s lean yes I’d look for a vacuum leak...what do your long term fuel trims look like both banks at idle ??...if they have not reached higher than 23% it will not set a lean DTC...a P0171/P074 !!...if the long terms fuel trims are higher than 10 % it is a concern...if your long terms are indeed higher than 10% run the engine at 3000 RPM for a few minutes...if you have a vacuum leak the short terms will go negative and the long terms will slowly follow !!...if fuel trims go from 10% to say 20% or higher at 3000 RPM you have either fuel delivery or MAF issues !!
If both O2 sensors are “fixed” lean in your case (below 450mv) spray some Brake Kleen into the engine and see if they respond by going rich (above 450mv) !!....you work at a Chevy Dealership ??m
PS— please include the year of your car in your thread to include current mods or in your profile...this helps us...“help you” !!..,and with a dirty MAF or air cleaner you will normally see negative fuel trims at idle that go positive at higher RPM !!
If both O2 sensors are “fixed” lean in your case (below 450mv) spray some Brake Kleen into the engine and see if they respond by going rich (above 450mv) !!....you work at a Chevy Dealership ??m
PS— please include the year of your car in your thread to include current mods or in your profile...this helps us...“help you” !!..,and with a dirty MAF or air cleaner you will normally see negative fuel trims at idle that go positive at higher RPM !!
Last edited by C5 Diag; Aug 25, 2019 at 09:03 PM.
