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. P0873 means switch C reports no pressure although its clutch should be applied. GM checks it when the 2-6 brake is commanded above 700 kPa and sets it after 15 counts on the 6L80 or 20 on the 2010 6T70, without MIL. Allison sets it after 0.125 s (2006) or 0.175 s (2007) without pressure at an applied valve, then tells electrical from mechanical by the companion solenoid code, 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
- Code stored in the gearbox module; on GM without MIL, on Allison with MIL
- Shift shock or slip in gears using clutch C
Most likely causes
- Signal wire or connector open (gearbox pass-through, harness)
- Pressure switch does not close (diaphragm, seal)
- Clutch pressure does not build: low fluid, leak, regulator valve
- Gearbox module input
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.
What each character of P0873 means
- P: Powertrain: engine and transmission
- 0: Generic code: same on every make
- 8: Transmission
- 73: Specific fault in that system
Frequently asked questions
Can I keep driving with code P0873?
Drive gently to a repair shop. If it slips, you hear clunks, or it loses its gears, do not keep driving.
What causes code P0873?
The most common causes are: signal wire or connector open (gearbox pass-through, harness); pressure switch does not close (diaphragm, seal); clutch pressure does not build: low fluid, leak, regulator valve.
Related codes
- P0870Transmission Fluid Pressure Sensor/Switch C Circuit
- P0871Transmission Fluid Pressure Sensor/Switch C Circuit Range/Performance
- P0872Transmission Fluid Pressure Sensor/Switch C Circuit Low
- P0878Transmission Fluid Pressure Sensor/Switch D Circuit High
- P0990Transmission Fluid Pressure Sensor/Switch E Circuit High
- P0761Shift Solenoid C Performance/Stuck Off
Sources
- gsi.ext.gm.com: 11OBDG07 TRANS Diagnostics
- gsi.ext.gm.com: 10OBDG08 TRANS Diagnostics
- gsi.ext.gm.com: 07 GRP15 Allison 1000
- 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.