This description is a little lengthy, but I was able to fix the P1271/P1275 problem on my wife's car, and since most forums I have seen seemed to end up with no resolution, with a trip to the junkyard the only solution, I think I may be able to help someone to keep from going crazy with this.
I got the P1271 and P1275 codes on my wife's 2002 GMC Envoy, and after going through all the forums, I still could not get the problem resolved. Several years after we bought the car used, we were going past Corsicana, TX, and got the Reduced power msg. We drove for miles with the car barely moving, but after diconnecting, then reconnecting the battery, I was able to get it running ok again. The car was still under dealer warranty, and the dealer replaced the power control module, but the problem came back a few months later and continued for years.
Several months ago I had to disconnect the connectors on the power control module to replace the valve cover gasket, but a few days later the
p1271 and P1275 errors began happening on a daily basis. I pulled the connectors off again (ALWAYS with the battery disconnected), inspected them, sprayed them with alcohol, put them back on, then off several times, as I used to do in repairing computers, blew them clean with my air compressor, then put them back on. The problem remained.
Finally, despite the warnings on the forums, I purchased the Accelerator pedal sensor from AutoZone ($80 plus), checked out both the old one and the AutoZone one with my needle meter, and the new one was not as smooth as the old one. To check I just put the ohmmeter on different pins on the sensor until I found the 4 configurations for the 2 sensors. You can't check it with a digital meter. You have to watch the needle move smoothly as you press on the pedal. It is the same as checking a throttle position sensor. The sensor arm slides on a circular coil, and if it gets worn, the needle will jump forward and backward erradically as it makes and breaks the connection instead of going up smoothly, and that will trigger the error.
Still I put in the new sensor, but it failed numerous times daily, more than the original sensor. I finally went ahead and bought the shop manual off Ebay, got the pin configurations, and proceeded to test. I tested the +5 volt wires at the accelerator pedal end (white/black +5, brown ground for sensor1, then tan +5 and purple ground for sensor2) using several state-of-the-art safety pins shoved into the holes and got 4.95 volts on each, which was perfect.
The power control module has 3 connectors, but the BLUE connector has the accelerator pedal wires. As the connector is plugged in, pin 1 is at the bottom right, pin 2 is next to it on the right (not across). The thin black plastic cover covering the wires can be popped off with a small screwdriver in case you have to push a pin back out. The connector is held on with just 1 screw, so after disconnecting the battery and pulling the connector back, I proceeded to stick wires into pin 2 and pin 10 to measure the resistance while pressing the accelerator pedal, when I noticed pin 2 was pushed way back into the socket. That appeared to be the problem. So with my handy dandy safety pin I pushed it back in and screwed the connector back in. Two days later my wife got the P1271 error again. So I pulled the connector back off, and the pin was pushed back in again. I stuck a wire into the pins around it with no problem, but the wire would not go into pin 2. The pin was defective. It had to have been defective when it came new from the dealer back in 2002, and the only connection it had was when the male pin was pushing against the female pin because it could not go in. I actually broke the pin trying to force it in, but a quick trip to Radio Shack and a new pin fixed the problem - but only for 2 days. AAAAUUUUUYUGGGGHHHGH!
Then removing the connector I ohmed out the wires going to the accelerator pedal while pushing in the pedal, and the needle on the meter jumped up and down like crazy. How could it have gone bad so soon? I put my meter back on the old pedal sensor, which appeared to be perfect, then took the new sensor out and put the old one back in. I then rechecked the new one I just took out, and it was normal again, though clearly not as smooth as the original OEM sensor. I have seen this occur many times when working on switches and circuit boards in computers. If you get the switch or board too tight, it warps and becomes erratic or doesn't work at all. So I made sure the old one I put back in was not screwed in too tight, rechecked it with my ohmmeter after it was installed, and it was still perfect. Also the accelerator pedal switch protrudes on both sides where the pedal swivels, so the metal mount in the car has a hole in it where the sensor protrudes, but the hole does not seem to match the sensor very well, so it could apply unneeded pressure if it does not line up.
Three weeks later with no errors and having clearly identified and resolving several problems leads me to believe the problem is fixed.
In summary:
(1) The original cause of the problem was a defective pin in the BLUE connector on the power control module.
(2) When replacing the original OEM sensor with the new Radio Shack sensor, I introduced a new problem. The new sensor was not as smooth as the OEM sensor.
(3) When I put in the new sensor, I got it too tight, and although it worked fairly well outside the car, it was very erratic in the car, and that caused the problem to continue. You have to recheck it in the car after it has been tightened down or you may just make the problem worse. Also the hole in the metal mount may not have lined up with the protrusion on the sensor, causing it to warp. Maybe a metal washer placed on each of the 3 screws between the the sensor and the metal mount would have moved the sensor out far enough so a misaligned hole would not have caused the sensor to warp.
In any case, mine is FIXED! Hope this bit of nerve-wracking info helps someone.