Powertrain, generic · Transmission

P0846 Transmission Fluid Pressure Sensor/Switch B Circuit Range/Performance

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

Transmission fluid pressure sensor/switch A and B are inputs inside the automatic gearbox. A switch only reports pressure present or absent, a sensor reports a value. The letter is the maker's choice: Allison 1000 uses A and B for the switches on shift valves S1 and S2, GM's CVT for the primary and secondary pulley sensors, GM's 2025 8-speed A for the lube pressure sensor; Ford reports pressure faults under its solenoid codes instead. P0846 is the plausibility fault of B. GM's CVT uses the same test as for A on its second pulley: pressure off target by 500 or 1500 kPa plus a ratio error above 0.2 for about 6 s, line pressure above 600 kPa, over 35 km/h, type A. Allison sets it when switch 2 stays without pressure 5 s after valve S2 is applied. On the Corvette dual clutch a sticking valve is the usual cause.

Likely causes

Dirty or sticking valve, worn valve body
Pressure sensor or switch drifting or sticking
Fluid level low, fluid aged or filter clogged
Mechanical damage: thrust washer, CVT belt or pulley, pump
Control module software

Symptoms

  • Check engine or transmission warning lamp on
  • Slipping or shift shock
  • CVT: ratio and power limited

Repair estimate

DifficultyHardWorkshop job
Parts and labour€150–2,500
Time1–8 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

P0845P0847P0848P0841P0868

References: gsi.ext.gm.com, gsi.ext.gm.com, static.nhtsa.gov.