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Auto Parts and Repairs
Oxygen Sensors
Check Engine Light
1995-2005 Chevy Cavaliers

Which sensor downstream or upstream causes the MIL light to come on?


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2004-11-22 10:13:00
2004-11-22 10:13:00

About 30 things can cause the light to come on. TAke it to auto zone and have the codes read for free.

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Get the check engine light looked at, the code will specify if it is the upstream or downstream sensor. The upstream will be on the exhaust manifold, and the downstream will be on the pipe after the catalytic converter.

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The upstream 02 sensor is usually located shortly after the exhaust manifold, before the converter. That is the one that controls how the car runs. The downstream sensor, after the converter tells the computer if the converter is doing it's job or not. It does not affect performance, but you might have to live with a check engine light being on. There are probably 2 of each on a V6.

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Upstream sensor located by engine,or downstream sensor in exhaust under car ,or if blinking ,possible catalytic converter failure

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NO, you cannot do this, this will compound your problem and eventually damage the engine and/or catalytic converter to the point that they/it must be replaced, all three failures are very expensive repairs. The faulty O2 sensor must be identified and replaced. There are 4 set-ups: Single sensor; Dual "upstream" <both sensors are pre-cat>; Dual upstream/downstream <one sensor is pre-cat, one sensor is post-cat> and Quad sensor <two sensors are pre-cat, two sensors are post-cat>. The upstream controls the fuel mixture and the downstream monitors the catalytic converter. BANK 1 is always the number 1 spark plug side and SENSOR 1 is always upstream. Once the fault is corrected the ECM must be cleared with a scanner to shut off the light.

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The code that came up should have specified a location. Left, right, upstream, downstream, etc.


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