Or you can go to your local AutoZone and they'll read it for free.

Or you can make it blink out codes yourself.  Here's the procedure from the
2002 Pathfinder service manual (I'm assuming it is the same for '01).

They recommend you use a watch with a second hand to do the timing on this.

1. Insure the accelerator pedal is fully released, then turn the ignition on
(warning lights on, but don't start the engine) and wait 3 seconds

2. Repeat the following procedure quickly five times within 5 seconds:
   1)  fully depress the accelerator pedal.
   2)  fully release the accelerator pedal.

3.  Wait 7 seconds.  fully depress the accelerator pedal and keep it down
for approximately 10 seconds until the MIL starts blinking.

4.  Fully release the accelerator pedal.  ECM has now entered Diagnostic
test mode II and will blink out self diagnostic results.

It blinks out 4 digit codes, 10 blinks represents the digit zero.  The 1,000
digit blinks on for .6 seconds and off for .6 seconds.  The other digits
blink faster - .3 seconds on, .3 seconds off.  Digits are separated by the
light going off for 1 second.  The change from one four digit code to the
next is indicated by the light going off for 1.8 seconds.

It keeps blinking out the code(s) until you stop it.  A code of "0000" means
no problems detected.

To erase the stored codes (and reset the light), while it is blinking out
the codes, press the accelerator pedal down and hold it for more than 10
seconds.  (If you don't want to erase/reset it, just turn off the key.)

Post whatever code(s) you get and somebody here will probably look it up for
you.