Testing the upstream oxygen sensors (O2S11 and O2S21), on your OBD II equipped 4.0L Ford Aerostar, Explorer, Ranger, or Mountaineer, can be accomplished in a few easy steps and in this article I'll show you how.
As you might already be aware, if you've done some research... quite a few things can cause the PCM (Powertrain Control Module = fuel injection computer) to think that the oxygen sensor or sensors have failed when they haven't. So testing them before replacing them is a good idea.
Here, at glance, are the main points of this article:
TIP 1: To test the O2 sensors, with the test info in this article, you'll need a scan tool that has Live Data capability.
You don't need an expensive $2K to $5K (US) scan tool to do it. I have written this article so that you can accomplish the O2 sensor tests with a generic scan tool (Don't have a scan tool? Need a scan tool? Check out my recommendation: Actron CP9580 Scan Tool).
TIP 2: The test info in this article will show you how to test the oxygen sensors in action and on the car... no need to remove them.
A failed or failing upstream oxygen sensor does not cause sever drive-ability issues. For the most part, your 4.0L equipped Ford vehicle will run pretty good. This doesn't mean you won't see or feel some symptoms. Here are the most common symptoms:
If you've been wondering exactly what the heck each Diagnostic Trouble Code means in plain English, this is the section for you:
P0131: Upstream Heated Oxygen Sensor (HO2S11) Circuit Out Of Range Low voltage (Bank 1).
P0133: Upstream Heated Oxygen Sensor (HO2S11) Circuit Slow Response (Bank 1).
P0151: Upstream Heated Oxygen Sensor (HO2S21) Circuit Out Of Range Low voltage (Bank 2).
P0153: Upstream Heated Oxygen Sensor (HO2S11) Circuit Slow Response (Bank 2).
The oxygen sensor test, in this article, will help you to diagnose any of the above Diagnostic Trouble Codes.
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