U0679 code meaning
Lost Communication With Transmission Fluid Pressure Sensor/Switch A
Network system Generic code U06xx codes Check engine light
What U0679 means
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.
U0679 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyHard
- Typical labor1 to 5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0679
- Harsh or delayed shifts
- Transmission stays in a fixed gear
- Check engine or transmission warning light
Common causes of U0679
- Most likelyTransmission internal harness or lead frame to sensor A damaged
- PossibleTransmission case connector leaking oil or corroded
- PossiblePressure sensor A electronics failed
- Less likelyTransmission control module input or software fault
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Transmission fluid pressure sensor aVehicle bus wiring
What each part of U0679 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 79 | The exact fault in that area. |
What to do next
- Note U0679 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U0679
What does U0679 mean?
U0679 means "Lost Communication With Transmission Fluid Pressure Sensor/Switch A". Automatic transmissions measure hydraulic pressure to confirm that a clutch or pulley really received the pressure the controller asked for. It is a generic code, so it means the same on every make.
Is it safe to drive with U0679?
Drive gently and only to a workshop. With U0679 the car can go into limp mode (reduced power) to protect itself.
Will U0679 fail an emissions test?
Yes, it can. U0679 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is U0679 to fix?
Difficulty: hard. A typical repair takes 1 to 5 hours of work. This is a job for a workshop.
Will U0679 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.