Check Engine Light On With Code PO138 Is That Before Or After Catalytic Converter Oxygen Sensor

Posted in Oxygen Sensors | Asked on Aug 12, 2010

If after the catalytic converter oxygen sensor where can i find a good website that shows how to replace it(DIY) with pictures/photos without buying haynes/chiltons repair manual ? would adding fuel injector cleaner/seafoam/or the tightening the gas tank lid works ?

There are 3 Answers for "Check Engine Light On With Code PO138 Is That Before Or After Catalytic Converter Oxygen Sensor"

  1. tech1 says:

    that code is pre cat easy to change and needs only a wrench

  2. Dave3507 says:

    PO138 21 Downstream H02S shorted to voltage Harness and connector / Downstream HO2S

    This code is for the O2 Sensor behind the cats.
    Your O2 Sensor has gone bad.

    The sensor is on Bank 1 Sensor 2. Meaning driver’s side, sensor behind the catalytic converters.
    This code is indicating the voltage the O2 sensor is detecting is too high. Generally a O2 sensor generates it’s own electricity and send the signal to the computer to control the air/fuel mixture or to check to make sure the Catalytic converters are working efficiently. They usually have a range of 1-5VDC. The OBDII Computer on your car is detecting a high voltage. In your case, the O2 sensor involved is checking to make sure your cats are working.

    When a O2 sensor goes bad, it is common to find this problem of high voltage triggering the code.

  3. tronary says:

    PO138 o2 sensor circuit high voltage (bank 1 sensor 2) This does not indicate a bad sensor. If it was bad there would be no signal or an erratic signal. High voltage could indicate a rich mixture in the exhaust system and possibly a bad cat. This sensor is after the cat. Bank one varies depending on where the # 1 cylinder is on the engine, left or right side. You need a scanner that can produce a graph to check o2 sensors properly. Injector cleaner in the tank may help as a dirty injector can cause rich mixture. You can add the cleaner and have Auto Zone or some auto supply turn off your check engine lite and wait to see if it comes back on. It won’t go off by itself. If your car is a little sluggich or is starting to lack power you have a cat.problem. A continuing rich mixture will damage the cat by overheating it. NEVER replace a part till you know the problem.

    http://www.autotap.com/technical_library.asp ^(http://www.carparts21.com/goto/http://www.autotap.com/technical_library.asp)
    Go here and get educated about sensors.

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