P0874: Transmission Fluid Pressure Sensor/Switch C Circuit Intermittent

What does P0874 mean?

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. P0874 reports short dropouts or flutter of the C signal without a lasting low or high. It is documented only in GM bulletin 21-NA-033 for the Corvette C8 dual clutch, with MIL: dirt and sticking valves are cleaned, the clutches relearned, and only then the circuit traced. Thresholds are not published.

The code tells you which monitor failed, not which part is broken. Test before replacing parts.

Symptoms

• Warning lamp coming and going
• Occasional harsh shift or limp mode

Common causes

• High Loose contact or corrosion at connector or harness
• Medium Dirt or sticking valve (dual clutch)
• Medium Sensor or switch with dropouts
• Low Low fluid level, pressure drops in corners

Likelihood is a general estimate across vehicles; your make and model may differ.