Powertrain, generic · Transmission

P0873 Transmission Fluid Pressure Sensor/Switch C Circuit High

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

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.

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

Symptoms

  • Code stored in the gearbox module; on GM without MIL, on Allison with MIL
  • Shift shock or slip in gears using clutch C

Repair estimate

DifficultyHardWorkshop job
Parts and labour€200–1,500
Time1–5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

transmission fluid pressure sensortransmission valve bodytransmission wiringtransmission control module

Related codes

P0870P0871P0872P0878P0990P0761

References: gsi.ext.gm.com, gsi.ext.gm.com, gsi.ext.gm.com, gsi.ext.gm.com.