Powertrain, generic · Transmission

P0845 Transmission Fluid Pressure Sensor/Switch B Circuit

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. P0845 is the general circuit fault of switch or sensor B. In GM's 2006 Allison table it belongs to the switch on shift valve S2: if the switch reports pressure for more than 0.04 s with the valve at rest, the valve is commanded again; if the fault persists, the case is classed as electrical (with P0768), mechanical or sporadic. Type A, MIL after one trip.

Likely causes

Pressure switch or sensor B faulty or stuck
Sticking shift valve or dirt in the valve body
Harness or connector at the gearbox: fluid wicking, corrosion, chafing
Fluid level low or fluid contaminated
Transmission control module faulty

Symptoms

  • Check engine or transmission warning lamp on
  • Limp mode with a fixed gear, harsh or missing shifts

Repair estimate

DifficultyHardWorkshop job
Parts and labour€150–900
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

P0846P0847P0848P0849P0840P0768

References: gsi.ext.gm.com, law.cornell.edu.