Damaged or chafed wiring harness between the pressure sensor/switch 'D' and the transmission control module; Corroded, loose, or water-intruded electrical connector at the sensor or switch; Internally failing transmission fluid pressure sensor or switch 'D' that works intermittently; Low or contaminated transmission fluid causing erratic pressure readings that trigger the intermittent fault; Faulty transmission control module or a software calibration issue affecting signal interpretation; Debris or sludge blocking the hydraulic passage to the sensor, causing pressure pulsations that confuse the sensor

DTC codes / P08xx · Transmission / P0879

P0879Transmission Fluid Pressure Sensor/Switch 'D' Circuit Intermittent

P0879 indicates that the transmission control module has detected an intermittent fault in the electrical circuit for transmission fluid pressure sensor or switch 'D', which is typically used to monitor pressure in a specific hydraulic circuit such as a clutch pack or line pressure. The circuit works correctly at times but cuts out or sends erratic signals, so the module cannot trust the pressure reading and sets this code.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaTransmission

Symptoms you may notice

Illumination of the check engine light or transmission warning lamp, often with no other noticeable symptoms
Harsh or delayed gear shifts, especially when the transmission is cold or under load
The transmission may enter limp mode, sticking in a single gear or refusing to downshift
Intermittent slipping or flaring during acceleration when the faulty circuit acts up
A stored code that clears itself and returns after several drive cycles

Common causes, most likely first

Damaged or chafed wiring harness between the pressure sensor/switch 'D' and the transmission control module
Corroded, loose, or water-intruded electrical connector at the sensor or switch
Internally failing transmission fluid pressure sensor or switch 'D' that works intermittently
Low or contaminated transmission fluid causing erratic pressure readings that trigger the intermittent fault
Faulty transmission control module or a software calibration issue affecting signal interpretation
Debris or sludge blocking the hydraulic passage to the sensor, causing pressure pulsations that confuse the sensor

How to diagnose and fix it

Verify battery voltage and ground connections, then clear the code and test-drive to confirm it returns
Inspect the sensor/switch 'D' connector and wiring for corrosion, chafing, or loose pins, repairing as needed
Check transmission fluid level and condition, topping off or servicing fluid if it is low or burnt
Back-probe the sensor signal circuit and monitor live data for dropouts while wiggling the harness and driving
Test the sensor/switch 'D' with a multimeter for resistance or voltage changes that match pressure changes
Replace the faulty pressure sensor or switch 'D' if electrical tests confirm it is failing intermittently
If all external circuits and the sensor test good, diagnose the transmission control module and its software calibration

Intermittent faults hide in plain sight

A code that sets only once every few drive cycles often points to a wiring harness rubbed through at a bend or near a hot exhaust component, not a failed sensor.
Technicians who replace the sensor without wiggling the harness under load frequently see the code return because the intermittent short or open was in the connector all along.
Low transmission fluid from a slow leak can cause pressure pulsations that make sensor 'D' report erratic values, so always check fluid level before condemning electrical parts.
On some vehicles, a failing transmission control module ground can mimic a sensor circuit fault, so voltage drop testing the module ground is a worthwhile step.
This code does not always mean the transmission is mechanically damaged; many cases are resolved with a connector repair or fluid service.

Can I keep driving with P0879?

You can usually drive the vehicle short distances to a repair shop, but avoid heavy acceleration, towing, or long highway trips because the intermittent fault can cause harsh shifts or sudden limp mode. If the transmission slips or refuses to shift, stop driving and have it towed.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.