We had a P2138 last May. There was a sudden loss of power and a SES light. We limped it home, I pulled the code, and rolled the dice on replacing the APPS without doing actual thorough diagnostics. IOW, I threw a part at the problem. I replaced the APPS myself. I didn't have time to shop around and get the best price on the part, I just bought it at the dealer the same day.
The Accelerator Pedal Position Sensor (APPS) is the pedal assembly minus the actual pedal. Part No. 18002-EH000, $250 at the dealer (May2012). It was in stock (what does that tell you?).
It took about an hour for me to replace, including taking pics. If you knew what you were doing, it could be done in a lot less time. I'm just now getting around to posting the pics, six months later
(click on any image for larger
The replacement APPS. The part you put your foot on does not come with it, but everything else does:
Pry up this cover:
Remove the 10mm nut below:
Next is the tricky part: removing the two plastic pins that retain the pedal to the link. Unless you know what you're dealing with, you'll break it (as I did). Fortunately, the part the breaks comes with the new APPS.
Use needle-nose pliers to squeeze the end of each pin. IIRC, the part needed to be squeezed on mine was facing the right side of the pedal, and I assume that bent-nose pliers would have been necessary.
I broke my link before I figured out how to remove the pins:
Better pic of the pins:
Jumping ahead of myself, here's the pedal with the new APPS:
Remove the vent from the left/upper side of the tunnel:
Carefully pull back the carpeting to reveal two more 10mm nuts to remove, then begin manouvering the old APPS down. I admit, I cannot recall if there was one more fastener higher, but I don't think so. Once you've begun to pull it down, you'll have to snake your hand to the top of it and remove one cable guide/clip, and then disengage the harness from the APPS.
Installation is the reverse of the above. Reconnecting the wire harness and the harness guide/clip was the hardest part of that.
When reassembled, run though the re-train procedure (search for it) to train the ECU to the new sensor. I cleared the P2138, retrained the ECU, and never had a recurrence of the problem.