My check engine light came on and when I took it to an Auto Zone they could not read the codes. It seems the module does not work. I looked for the obvious loose wires but it looked OK. I disconnected the battery to reset the light but it came back on after a short while. I took it to another store to try again and again his code reader was getting no signal.. Where do I go from here? The truck runs OK but I want to check things out and take care of any potential problems.

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2001 Ranger Edge 3.0 2WD 108000 miles