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U0679 Lost Communication With Transmission Fluid Pressure Sensor/Switch A

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

Automatic transmissions measure hydraulic pressure to confirm that a clutch or pulley really received the pressure the controller asked for. Which sensor is A varies: Ford's 2024 summary calls the sensors of its 10R60/10R80 and 8F units TFP A and B, analog with 0.5 to 4.5 V for 0 to 2,500 kPa, and sets P0841 when the reading sticks although the clutch still applies and releases. GM's 24OBDG07 assigns A to clutch 1 (P0842 below 220 mV, P0843 above 4,530 mV after 150 ms), while its CVT table 25OBDG03A uses A for the primary pulley. U0679 covers a digital sensor A that has gone silent. No manufacturer documents this code publicly. The transmission controller then loses its pressure feedback and may hold a gear or shift harshly.

Likely causes

Transmission internal harness or lead frame to sensor A damaged
Transmission case connector leaking oil or corroded
Pressure sensor A electronics failed
Transmission control module input or software fault

Symptoms

  • Harsh or delayed shifts
  • Transmission stays in a fixed gear
  • Check engine or transmission warning light

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–1,200
Time1–5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

transmission fluid pressure sensor avehicle bus wiring

Related codes

U067AP0840P0841P0842P0843P0844

References: fordservicecontent.com, gsi.ext.gm.com, gsi.ext.gm.com.