Question about 2001 Buick LeSabre

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How do I find out Which Oxygen Sensor is Bad, Upstream or Down-Stream ?? I Pop 2 Error Codes. #1- Spark Plugs, #2 O2 Sensor(s) [doesn't designate which one as my Car has 2]

3.8L V-6 Started out as a Intermittent Issue, Service Engine Light ON, later it went OFF, after 3 weeks of this, Light stayed on Continuous. Took it to an Auto Zone they Plugged In and It Popped the 2 Codes (Sorry misplaced the Codes). Plan on Replacing Plugs anyways. But, on the O2 Issue seems to be a Puzzle, and I really don't want to R & R 2 Parts if I don't have too.

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  • Red Wymer
    Red Wymer Apr 09, 2015

    Well Tried the Additive, and ran the Car for about 140 miles Freeway & stop 'n Go Traffic...Gas Consumption Decreased a Bit, Est. Mileage Increased a Bit, However still getting Hard Starting, AND Rough Idle (Cold)



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With out the codes cant tell which o2 sensor is causing the issue , before you change any sensors i'd recommend using a fuel addative , get one that cover the catalytic convertor as well as fuel and engine parts , give it a long run at a good speed to get the engine to a high operating temperature as most o2 sensor issues are because the tip is coated in carbon etc and cant detect the exhaust gases, another thing to check before replacing o2 sensors is the air intake pipe work as a split , tear etc in the air intake side will give a false reading on the exhaust side as the intake readings are affected by the split , hope this helps

Posted on Mar 30, 2015

Testimonial: "I have always been a Firm believer in Seafoam, so would One (1) Can be ample in a 16 Gallon Tank, or Two (2) Cans?? When I add this additive would it be better to run a Higher Octane Fuel than Regular Unleaded??"

  • 3 more comments 
  • steve Apr 01, 2015

    Hi, i'm in UK and we don't have seafoam over here , the addatives i could recommend are WYNNS or REDEX , both are available on the internet if there not in your stores , as i said make sure you get one that covers the cat convertor as well

  • Red Wymer
    Red Wymer Apr 01, 2015

    OK, found the Codes: P0171, P0102, P0300

  • steve Apr 01, 2015

    Hi Red, the codes as follows P0171 Lean fuel mix,P0102 Low air mass input,P0300 random misfires, these all could either be caused by a faulty o2 sensor or a leaking or worn, split in the air intake circuit ,i would check very carefully all the air intake hose's especially the ribbed ones for any sign of wear etc , then if all ok i would go ahead with the fuel addative which MUST cover the catalytic convertor , keep me posted when you have tried these steps and good luck

  • Red Wymer
    Red Wymer Apr 09, 2015

    Tried the Additive, Est. Mileage & Fuel Consumption Improved a bit, However, it is still Hard Starting, and Rough Idle (Lower than required) on a Cold Engine. When it warms up to Operating Temp. Idle improves but still not smooth...Highway Driving is Fine, Around Town is a Bit Sluggish

  • steve Apr 09, 2015

    change the plugs as you previously intended and have the codes reread , if no better get the cylinder compressions read , dont know your mileage but 14 years old engine may have low compressions, there are a few things that could cause these symptoms , as cant see vehicle i can only suggest the next step i would recommend keep me posted



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2 Answers

Where is the O2sensor bank 1 at with a code of P0420. AND do I need to replace both sensors upstream and down. Or just the one that is showing up on the obd scanner.

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One would need the year, make, model, and engine size to tell you exactly where they are and how many.

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So some older cars have only one o2 sensor. Not far from the engine in the exhaust stream. Some newer cars with dual exhaust (2 converters) may have four o2 sensors. 1 for each bank of the engine and 1 behind each catalytic converter. A 2005 Buick Century with a 3.1L engine, for instance, has only two o2 sensors: one (upstream) in the exhaust down pipe, and one (downstream) just behind the catalytic converter.

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What does po135, p1131, and p0305 mean on a ford f250 with a 4.6L 2007

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The misfire on cylinder 5 on the right side of the engine, 2nd one from the front, could be something as simple as a fouled spark plug or a coil malfunction.

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