P0871

P0871 sets when the overdrive (5th gear) hydraulic pressure switch returns an open or shorted state inconsistent with the commanded gear, most commonly on 5-speed and 6-speed automatics that use discrete pressure switches inside the valve body rather than full analog sensors. Cheapest first: verify transmission fluid level and condition at operating temperature, because low fluid or aerated ATF prevents the OD circuit from reaching pressure switch close-threshold (typically 30-60 psi) even when the solenoid is commanded on. Scan-tool the OD pressure switch PID and command a 4-5 upshift on a road test; the switch should toggle from open to closed within 0.3 seconds of the OD apply solenoid command. Caveat: the OD pressure switch is almost always integrated into the solenoid pack or valve body, so replacement is rarely sensor-only.

Vehicle-specific patterns: 2002-2010 Dodge Ram and Durango with the 545RFE shows P0871 most often from a stuck OD accumulator piston, not the switch, and the Sonnax accumulator repair kit is the durable fix. 2004-2010 Ford Explorer and F-150 with the 5R55W/5R55S sees P0871 from solenoid pack internal pressure switch failure at 80-120k miles. 2005-2013 Nissan Frontier and Xterra with the RE5R05A throws P0871 when valve body wear lets OD pressure bleed off below switch threshold. 2007-2012 GM with the 6L80 in early Silverado and Yukon applications sees the OD switch fail on the TEHCM. Estimated repair: $380 to $1900.