3 Oxygen sensors and it did not tell them which one was bad

JOHN_H

MEMBER
2001 DODGE CARAVAN
6 CYL
AWD
AUTOMATIC
123,000 MILES

2001 Dodge Grand Caravan ES AWD with 3.8l engine I have a check engine light and brought it to AutoZone for a reading. They told me it was an Oxygen Sensor. They said there were 3 sensors and it did not tell them which one was bad. Any ideas on how to determine which one is bad without spending the money for all 3? (I was going to buy one and go around swithcing them out). NOTE: I already tried to "clear" the code, but the check engine light came back on within a week. Thank you!

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CH112063

MECHANIC
1,320 POSTS

Upstream o2 sensor before catalytic converter, downstream o2 sensor in back of catalytic converter. This way the PCM can test he catalyst at all times when hot and in a closed loop condition. The scanner will always say upstream or downstream. OK

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Saturday, May 8th, 2021 AT 5:37 PM

CH112063

MECHANIC
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Upstream o2 sensor in front of cat. Converter downstream o2 sensor is behind cat converter. The PCM compares these two to check the converter at all times. Try a different scanner, it will specify which one is not giving a proper response while hot in closed loop. OK be careful

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Saturday, May 8th, 2021 AT 5:37 PM

JOHN_H

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4 POSTS

Thank you. I'll go to Advance Auto instead of AutoZone and use their scanner. Hopefully it gives the detail needed. I also read somewhere that if I turn the ignition OFF-ON, OFF-ON, OFF-ON it shows the code on the digital mileage readout as Pxxxxx. I am on a biz trip right now, but will try both of these when I return.

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Saturday, May 8th, 2021 AT 5:37 PM

JOHN_H

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The OFF-ON, OFF-ON, OFF-ON trick worked! It showed P0135 (upstream 02 sensor) is faulty! .I ordered an upstream o2 sensor from RockAuto. Since I heard it was a real pain to replace this one, I am going to bring it to my favorite garage for them to replace it for me (plus some other work of course). I will let you know if this works.

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Saturday, May 8th, 2021 AT 5:37 PM

CH112063

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Yeah, good Idea, if after replace ment, the code shows up again, remember that it only senses oxygen, it may be good, but it is showing amount. Tell me if you still need me. Joe

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Saturday, May 8th, 2021 AT 5:37 PM

JOHN_H

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Yup, this worked! I just got the van back from my mechanic. I purchased the Denso O2 front (upstream) oxygen O2 sensor from RockAuto for just over $50 and paid my mechanic $50 to replace it. So, I now have it all working for $100. Much cheaper than having my dealer do it - I believe the sensor alone was $100.

Thanks for all the help!

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Saturday, May 8th, 2021 AT 5:37 PM

CH112063

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Yeah, it is expensive. It will tell the engine how to adjust its fuel and timing delivery. If one or more injectors or if fuel pressure is low, a code will come back. The replacement is I believe the same size wrench as a spark plug but it has the wire, so it is 50 bucks just for the socket. I have had some good luck with Nippodenso. Good. If gas is going to exist, there will soon be at least 5 and even 12 o2 sensors and who knows how many valves. I'm glad to hear you are ok.

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Saturday, May 8th, 2021 AT 5:37 PM

SQM

MECHANIC
6,383 POSTS

Hello,

I have attached the oxygen sensor replacement procedures for anyone else might be looking to replace them.

Also included troubleshooting steps for the code P0135.

Please let me know of any questions.
Thank you.

https://www.2carpros.com/articles/how-to-replace-an-oxygen-sensor

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