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]
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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Re: How do I find out Which Oxygen Sensor is Bad,...
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
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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.
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.
Hope this helps you or future parties of intrest. P1131 Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 1 P1151 Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 2 I would get under your stang and gently clean outside portion of o2 sensors using a scotch brite. Also if you have so dielectric grease pull electrical connections to o2 sensors clean them and add grease. These trick eliminated the o2 sensor OBD1 codes on my 1987 Ford mustang gt
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
It looks like you have two separate issues happening. Bank 1 would be the left side of the engine if you were standing in front of the truck looking at the engine. The "upstream" oxygen sensor will be on the exhaust pipe coming from the bank one side of the truck IN FRONT of the catalytic converter. From the codes, it appears that the upstream sensor has gone bad, but the oxygen sensor behind the catalytic converter, or "down stream" is fine.
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.
To identify if it is a bad coil, swap the #5 cylinder coil with another coil, and see if the misfire follows the relocated coil.
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.