www.transmissionrepaircostguide.com
Typed "P0871" into Google and you can read articles until blue in the face. The above link has a decent overview of the issue.
A few comments, not just for this specific code but all codes in general:
- While in the description it mentions fluid pressure sensor or switch, the codes does NOT say that the only possible issue is a bad sensor. It is saying that the signal the ECM is receiving from the sensor is outside of normal range. Point being just don't blindly go throw a new sensor at it. While it could be a bad sensor, it could also be the sensor is working correctly and saying something else is causing the pressure to be off.
- Are you experiencing any of the symptoms stated in the article, besides just the check engine light? You can determine if the code is active or store with a scanner. Check engine and other warning lights don't necessarily only come on when the problem is active. For example, there is always a chance the ECM read a low trans pressure for maybe 5 seconds which is long enough to trigger the light, then the pressure went back to normal. The check engine light will remain on for a certain period of time or until "cleared" with an OBD reader. Most codes will keep the check engine light on for a certain number of key cycles even if it's not active (the issue does not continue to occur. If there are no obvious driveability issues it's pretty common to clear the code and see if it comes back on or not.
- The article has some basic recommendations for trouble-shooting the issue. Always start with the easy and free/cheap ones before starting to throw parts at it. For this code some of the causes could simply be low trans fluid level, dirty (dark/black) trans fluid, the engine getting hot, and do a visual inspection of all of the wiring around the trans for signs of obvious damage.
