Powertrain, generic · Transmission

P0872 Transmission Fluid Pressure Sensor/Switch C Circuit Low

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. P0872 means switch C reports pressure while its clutch is exhausted. GM checks it only when the 2-6 brake is commanded below 50 kPa, after a temperature-dependent delay, and counts one fault per clutch change: 10 on the 6L80, 18 on the 2010 6T70; listed as 'special no trip', without MIL. Allison 2007 sets it when switch 3 reports pressure for over 20 ms with the valve at rest, type A.

Likely causes

Pressure switch stuck closed or shorted internally
Signal wire shorted to ground inside the gearbox
Clutch circuit does not exhaust: dirt, sticking valve
Gearbox module

Symptoms

  • Code stored in the gearbox module; on GM without MIL, on Allison with MIL
  • Harsh shifts, possibly substitute gear

Repair estimate

DifficultyHardWorkshop job
Parts and labour€300–1,500
Time1.5–5 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

P0870P0871P0873P0877P0989P0762

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