Powertrain, generic · Transmission

P0849 Transmission Fluid Pressure Sensor/Switch B Circuit Intermittent

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. P0849 reports short dropouts of the B signal. GM bulletin 21-NA-033 for the Corvette C8 dual clutch lists it with P0841, P0844 and P0846: first the valves are cleaned and the clutches relearned, and only if the code comes back on its own is the circuit traced. Like the A counterpart P0844 it has no published thresholds.

Likely causes

Loose contact or corrosion at the gearbox connector or control unit
Dirt in valve or sensor causing signal jumps
Sensor faulty internally
Chafed spot in the harness

Symptoms

  • Warning lamp coming and going
  • Occasional shift shocks
  • Brief limp mode

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€100–800
Time1–4 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

P0845P0846P0847P0848P0844

References: static.nhtsa.gov, static.nhtsa.gov, law.cornell.edu.