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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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โˆ™ 2004-11-22 10:13:00
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Q: Which sensor downstream or upstream causes the MIL light to come on?
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How do you know which oxygen sensor is bad in a 2002 Dodge Caravan?

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.

What could be the cause of the emission control warning light to come on in a 2009 KIA RIO LX?

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

Where is the upstream oxygen sensor located on a 1999 Ford Taurus SE with a 3.0L V6 engine and how do you go about changing one if only the upstream is bad do i need to change the downstream as well?

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.

Can you wire two oxygen sensors to the same wires to get rid of my check engine light?

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.

2001 mistsubishi montero sport unlimited and the check engine light comes on because of a O2 sensor which one do you replace?

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

Where is the O2 sensor on an Oldsmobile alero?

That would depend on the size of the engine as well as if you are looking to replace the upstream sensor or downstream. Upstream simply means its in the exhaust system BEFORE the catalytic converter while downstream means that it is located after the converter. You need to have someone pull the DTC's, diagnostic trouble codes, from the ECM before you start replacing sensors. The code(s) you pull from that should point you in the right direction to which sensor is giving you a SES light or Check Engine light. I just recently pulled code P0420 on a 2000 Alero with the Quad4 engine. The code simply stated that the output on sensor 1 bank 1 was below threshold. I replaced the sensor and now everything is kosher. Some instances arent that lucky. Good luck with whatever you determine the cause is. Dale

On a 01 Dodge Caravan how do you know if you need a upsteam or downstream sensor?

The engine light code should say which is needed.

What causes the abs dashboard light to appear in a 2001 expedition?

light sensor

Would light come on if problem with catalytic converter?

If it has a downstream O2 sensor the check engine light will come on but if it does not the light may not come out. In most instances it will set the check engine light.

Where is the oxygen sensor reset 2002 Celica GTS?

There are two sensors in the exhaust system and both are located underneath the car. One upstream sensor that is before the catalytic converter (sensor 1, closest to the manifold) and one downstream of the converter (sensor 2). On a diagnostic tester, the code will come up Bank1 Sensor One or Bank1 Sensor Two. There is only one bank and two sensors. Once the sensor has been replaced, disconnect the negative battery terminal for about one minute and reconnect it. If the sensor replaced is installed correctly, the check engine light should go out and remain off.

What is the code p1405?

The code P1405 on a Ford means: PFE Sensor Circuit Upstream Hose. This code is usually caused by a faulty engine light.

S class 221 changed the lambda sensor upstream check engine light still comes on?

There is another problem. see related questions.

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