Powertrain, generic · Transmission

P0847 Transmission Fluid Pressure Sensor/Switch B Circuit Low

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. P0847 means the B signal is too low. Allison sets it when switch 2 reports pressure for over 0.04 s although valve S2 is at rest, type A; GM's CVT when the second pulley sensor falls below 3 % duty cycle for 0.3 s within 0.5 s, type A. Mitsubishi's bulletin for the F1CJC CVT asks for this circuit check before belt or pulleys are blamed.

Likely causes

Signal wire shorted to ground or, on GM duty-cycle sensors, open
Switch stuck closed or sensor faulty internally
5 V supply of the sensor missing
Shift valve stuck in the applied position, so the switch reports pressure correctly
Input of the control module faulty

Symptoms

  • Check engine or transmission warning lamp on
  • Limp mode with a fixed gear, harsh or missing shifts
  • CVT: ratio and power limited

Repair estimate

DifficultyHardWorkshop job
Parts and labour€120–900
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

P0845P0846P0848P0842

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