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Cod 51 means o2 sensor is bad but tell me please which o2 sensor is bad .upstream or down stream sensor

We located the mulfunction .its on o2 sensors but I am in doubt because I dont know which o2 sensor is bad downstream or up stream sensor

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  • 318 Answers

Oxygen sensors code sometimes produced because of some other problem, blocked exhaust or cat converter, over rice fuel supply or vacume leak in intake manifold giving a real lean mix and so o2 out of range in both casesw

Posted on Dec 10, 2012

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Posted on Jan 02, 2017

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SOURCE: Upstream O2 sensor location?

That is the first sensor closest to the engine. The downstream sensor is the one behind the converter.
Good luck.
Please rate this response , and let me know if ya need more help!

Posted on Aug 31, 2008

motor1258
  • 6674 Answers

SOURCE: 1997 Dodge Stratus V6 oxygen sensor location

Upstream, as in ahead of the converter, back toward engine. Start at converter and work your way back, should be on exhaust pipe or even on manifold.

Posted on Jan 11, 2009

emissionwiz
  • 76682 Answers

SOURCE: Does my 1999 Mercury Mystique have 4 O2 Sensors or am I wrong?

the sensors before the catalytic converters are the upstream sensors, the ones after the after the catalytic converters are the down stream sensors, Ford calls them the Catalyst efficiency monitors.

Posted on Apr 26, 2009

SOURCE: Getting PO141 trouble code when scanning! Car '03 accord, 2.4 ltr

i spoke to a honda tech , and he confirmed code p0141 on the 4cylinder model is the second sensor.

Posted on Aug 28, 2009

  • 105 Answers

SOURCE: 2001 elantra replaced cat o2 sensor upstream and

In reading what you've already done, I would suggest a Compression Test along with a vacuum gauge hooked up to the intake manifold. It may be that you're burning oil through your exhaust system in the catalytic converter. I've seen this with leaking or inoperative turbo-chargers. Pull all of your spark plugs, marking them as to what cylinder they went in with a Sharpie and if worn, replace them. Check the distributor cap & rotor button for wear or cross-firing. A Haynes Manual for your vehicle is available through most part stores which is truly effective for your DIYer. Bad plug wires can send unburned gases down through both O2 Sensors and the Catalyst. You may also want to check the plug wires and the coil(s). A fast way of checking plug wires is to grab all of them with your hand with the vehicle running and if you get "zapped"...you need spark plug wires. Remember, the codes you pull are just a general starting point as to where to start your diagnostics, not the exact problem itself. The computer doesn't monitor the mechanical aspect of your engine nor the fuel supply. The computer will take this as a given, so don't forget that when testing that it could be a compression problem or fuel problem, but as I first said...an oil leak fouling your exhaust system such as an inoperative EGR valve or oil leak on the exhaust side of the valve train.

I hope this Helps,

"00 Buck"

Posted on Jul 18, 2010

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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.


Bank one is front side of cat. It should also tell u if it's cat 1 or cat 2. Depending on make an modle an yr. Catalyst 1 bank 2 is left cat back sensor. Catalyst 2 bank 2 is right cat back sensor. U do not have to replace upstream also. My o2 sensor Catalyst 2 bank 2 went bad. Had engine code for burning rich bank 2. Replaced tha down stream sensor an fixed problem runs better an better gas. This was in 97 gmc suburban. Idk what vehicle ur askin about. An I'm not to familiar with much about cars jus trucks an suvs.

Jan 02, 2017 | Cars & Trucks

1 Answer

Where are o2 sensors location


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

O2 sensors are always in the exhaust stream, either in the exhaust manifold that is attached to the engine, or in the exhaust piping after the exhaust manifold. Some models have one for each bank of the engine, and some have only one sensor to monitor oxygen content. These engine sensors that the computer uses to "fix" or adjust the air/fuel ratio are called the upstream oxygen sensors. If the car is equipped (as most are today) with an oxygen sensor after the catalytic converter, this is called a downstream oxygen sensor. They are the same and do the same thing, but the downstream sensor is only used to monitor the efficiency of the converter. The upstream sensor(s) are what the computer reads to adjust or "trim" the fuel delivery.

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.

Aug 16, 2014 | Cars & Trucks

1 Answer

How many oxygen sensors are there on a 1996 ford explorer 8 cyl., 4.0 eng.


The answer depends on the type of exhaust system you have. You will have either 3 or 4 total O2 sensors on your V8. If you have single exhaust with a single catalytic converter then you will have 3 O2 sensors (2 upstream sensors & one downstream sensor - "up or down stream" meaning before of after the catalytic converter). If you have either dual exhaust and/or two catalytic converters then you have 4 O2 sensors (2 upstream & 2 downstream). If you have an MIL light (malfunction indicator light, or "check engine light") the code will indicate "front bank / bank one", which is one of the 2 upstream O2's before the catalytic converter(s), or "rear bank / bank two", which is one of the O2's after the catalytic converter(s).

Apr 22, 2012 | 1996 Ford Explorer

1 Answer

Downstream oxygen sensor location


Down stream o2 is always located after the catalytic converter,,Upstream o2 are before..The down stream o2 reads the effienciency of the converter

Sep 12, 2011 | 2006 Chrysler Town & Country

2 Answers

OXYGEN SENSOR ID


Only way to tell is count the number of wires coming from it. You also need to know if its the right or left bank and upstream or down stream. Upstream is before cat converters and by or in exhaust manifolds, down stream is behind converters and only measures converter effeciancy.

Mar 08, 2010 | 2001 Volkswagen Passat

1 Answer

I have 2008 toyoya tocoma truck only getting 13 mpg. the check engine light on, had it scope out said o2 sensor open, replced sensor had light cancel but came back on. still have problem


Are you sure you replaced the right 02 sensor? Some vehicles have up to 4 02 sensors and being the ones that have a seperated duel exhaust system. You will have an 02 sensor located upstream of the catalytic converter and one down stream of the converter so make sure you replaced the right on. If you used a scanner to tell you it was an 02 sensor it should have also told you bank one or bank two which translates to drivers side or passengers side will also tell you up stream or down stream.

Dec 01, 2009 | 2008 Toyota Tacoma

2 Answers

Im confused my car is a toyota camry 6cyl not 4cyl and some say it has 4 o2 sensors and others say it has 2, hum, wich is it???? please help and also is there a site where it shows me like a diagram as to...


I have no diagram,but there is what they call upstream,and down stream locations.Upstream,is above the cat-converter,the down stream is below the cat-converter.This would be per-side.You have a left,and a right exhaust manifold.The exhaust pipes run from each manifold(left and right)to the catalytic converters.So you would have to have on the left side a up stream o2 sensor,above the catalytic converter.and a down stream o2 sensor,below the catalytic converter.this would also be on the right side also,this would be the total of four(4) o2 sensors.I hope this is helpful.

Oct 16, 2009 | 1998 Toyota Camry

2 Answers

Exact location of downstream O2 sensor.


Downstream O2 sensor is after (downstream) the catalitic converter on the exhaust pipe. Upstream O2 sensor is after (downstream) the engine exhaust manifold - before (upstream) the catalitic converter. Upstream O2 sensor controls air-to-fuel ratio to yield a small excess oxygen. Downstream O2 sensor assesses the catalitic converter performance.

Sep 22, 2009 | 2003 Pontiac Vibe

1 Answer

Which O2 sensor for 2005 Dodge Ram Quad 5.7 (Hemi); the parts stores asked if I needed the 2,3 or 4 wire. My Vin starts with 1D7HA18DXXXXXXXXX


Which O2 sensor do you need, you have 4 O2 sensors in your Dodge ram. Is it the O2 sensor upstream or the down stream. I believe the down stream will have the 4 wire lead and the up stream will have the 3 wire leads. If you need the down stream O2 sensor which is the common one to go bad, you can look at the wire harness clip which is only 6 inches a way form the sensor after the catalytic converter. Good luck and hope this helps.

Jun 03, 2009 | 2005 Dodge Ram 1500

1 Answer

Installing 02 sensors


"Up-stream" means before the catalytic converters and are probably in the header pipe(s). The "down-stream" O2 sensors are behind the cats in the exhaust system, usually just behind them. Not the expert here on this particular car but there are probably 4 of these sensors. BMW exhaust systems are very tight on space, be careful tackling this job.

Jun 10, 2008 | BMW 545 Cars & Trucks

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