Worn or burnt friction plates on clutch or band B, reducing its ability to hold torque; Low transmission fluid level caused by a leak, preventing proper hydraulic pressure to apply the element; Degraded transmission fluid that has lost its friction modifiers and viscosity, leading to inconsistent clutch engagement; Sticking or leaking valve body solenoids or shift valves that control fluid pressure to element B; Failed or contaminated transmission fluid pressure sensor giving inaccurate feedback to the control module; Internal seal failure or cracked piston in the clutch pack for element B, causing pressure loss; Wiring or connector issues at the transmission control module or solenoid pack that interrupt control signals

DTC codes / P07xx · Transmission / P079B

P079BTransmission Friction Element B Slip Detected

Q: What does code P079B mean?

Transmission Friction Element B Slip Detected. P079B indicates that the transmission control module has detected an excessive amount of slip in friction element B, which is a clutch or band inside the transmission that engages a specific gear ratio. The computer compares input and output shaft speeds and flags the code when the expected speed reduction does not match what the sensors report, meaning the friction element is not holding as it should.

P079B indicates that the transmission control module has detected an excessive amount of slip in friction element B, which is a clutch or band inside the transmission that engages a specific gear ratio. The computer compares input and output shaft speeds and flags the code when the expected speed reduction does not match what the sensors report, meaning the friction element is not holding as it should.

SystemPowertrain

Code typeGeneric (all makes)

SeverityHigh

Fix difficultyProfessional

AreaTransmission

Symptoms you may notice

Illumination of the check engine light or transmission warning light, often with no other noticeable symptoms at first
Harsh or delayed shifts, especially when the affected gear is engaged
Slipping sensation during acceleration, where engine speed rises without a corresponding increase in vehicle speed
Transmission may enter limp mode and stay in a single gear to protect itself
Shuddering or vibration during gear changes that involve friction element B
Poor fuel economy or elevated transmission fluid temperature due to prolonged slip

Common causes, most likely first

Worn or burnt friction plates on clutch or band B, reducing its ability to hold torque
Low transmission fluid level caused by a leak, preventing proper hydraulic pressure to apply the element
Degraded transmission fluid that has lost its friction modifiers and viscosity, leading to inconsistent clutch engagement
Sticking or leaking valve body solenoids or shift valves that control fluid pressure to element B
Failed or contaminated transmission fluid pressure sensor giving inaccurate feedback to the control module
Internal seal failure or cracked piston in the clutch pack for element B, causing pressure loss
Wiring or connector issues at the transmission control module or solenoid pack that interrupt control signals

How to diagnose and fix it

Check transmission fluid level and condition; top off or replace fluid if it is low or burnt-smelling
Inspect for external fluid leaks at the pan, cooler lines, and seals, and repair as needed
Use a scan tool to read live data and compare input and output shaft speeds to confirm slip under load
Perform a pressure test at the transmission test ports to verify hydraulic pressure to element B
Remove the transmission pan to inspect for debris, clutch material, and check solenoid resistance and operation
If internal wear is confirmed, remove and disassemble the transmission to replace the affected clutch pack or band and reseal the unit
After repairs, clear the code and perform a relearn or adaptation drive cycle to verify the fix

What a slip code really tells you

A P079B can be set by a simple low fluid level or a clogged filter, so always verify fluid condition and level before condemning the transmission internals.
The code does not always mean the friction element itself is worn; a faulty pressure solenoid or a sticking valve can cause the same slip symptom by delivering incorrect pressure.
Some vehicles use adaptive shift strategies that can mask early slip, so the code may appear only after the wear has progressed significantly.
A contaminated mass airflow sensor or engine performance issue can alter engine torque calculations and indirectly trigger transmission slip codes, so check engine data first.
After replacing a clutch pack or valve body, many transmissions require a adaptive relearn procedure; skipping it can cause the code to return immediately.

Can I keep driving with P079B?

Driving with P079B is not recommended because continued slip generates excessive heat and can turn a repairable clutch wear issue into a complete transmission overhaul. If you must move the vehicle, keep speeds low, avoid hard acceleration, and have it diagnosed by a transmission specialist as soon as possible.

Tools that help

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