Transmission fluid pressure switches C and D report whether a clutch circuit is pressurised. They are more widespread than A and B: GM's 6L80/6L90 and 6T40/6T70 six-speeds put switch C on the 2-6 brake and D on the 1-2-3-4 clutch, Allison uses them for its third shift valve and its reverse switch, Ram's RFE gearboxes for the clutch pressure switches in the solenoid block. Ford reports pressure faults under its solenoid codes. P0871 means the switch does not follow the command or gear. On Ram's RFE it is the overdrive clutch switch: open in gears 1 to 3, closed in 4 to 6; it closes at about 1.5 bar and opens at 0.75 bar. Sonnax blames worn valve body bores in about 90 % of cases; on 2024 trucks it came with P0868 from a broken rear thrust washer. Allison 2006: switch without pressure 5 s after command, type A.
Medium severity. Can I keep driving?Drive gently to a repair shop. If it slips, you hear clunks, or it loses its gears, do not keep driving.
Symptoms
- MIL or transmission warning lamp on
- Limp mode, often in 2nd or 3rd gear
- Harsh engagement, neutral feeling in 4th gear
Most likely causes
- Worn valve body bores or shift valve plugs
- Mechanical damage: thrust washer, clutch seals
- Pressure switch faulty (lip seal)
- Dirt or sticking valve (dual clutch)
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: hard
- It can trigger limp mode.
- It affects emissions.
What each character of P0871 means
- P: Powertrain: engine and transmission
- 0: Generic code: same on every make
- 8: Transmission
- 71: Specific fault in that system
Frequently asked questions
Can I keep driving with code P0871?
Drive gently to a repair shop. If it slips, you hear clunks, or it loses its gears, do not keep driving.
What causes code P0871?
The most common causes are: worn valve body bores or shift valve plugs; mechanical damage: thrust washer, clutch seals; pressure switch faulty (lip seal).
Related codes
- P0870Transmission Fluid Pressure Sensor/Switch C Circuit
- P0872Transmission Fluid Pressure Sensor/Switch C Circuit Low
- P0873Transmission Fluid Pressure Sensor/Switch C Circuit High
- P0876Transmission Fluid Pressure Sensor/Switch D Circuit Range/Performance
- P0868Transmission Fluid Pressure Low
- P0841Transmission Fluid Pressure Sensor/Switch A Circuit Range/Performance
Sources
- sonnax.com: 1438 dodge rfe pressure switch diagnosis code p087
- gearsmagazine.com: dodge rfe pressure switch diagnosis and code p0871
- static.nhtsa.gov: MC 11014507 0002
- gsi.ext.gm.com: 2006trans9
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.