What Does P079B Mean?
The TCM has detected slippage in transmission friction element B. This friction element is not fully engaging during its commanded apply state, allowing rotational speed differences across the element. This slip may be felt as RPM flaring during shifts, delayed engagement, or a general lack of power transfer in the gears where element B is active.
Safety Warning
Slippage in friction element B can cause unpredictable power delivery and RPM flares. The vehicle may lose drive power momentarily during acceleration. Limit driving to essential trips only and avoid highway speeds. Continued operation will worsen damage rapidly.
Common Causes
35%
Worn friction element B clutch pack with reduced friction material
25%
Low or degraded transmission fluid causing insufficient clutch apply pressure
15%
Leaking piston seals or apply circuit for element B
15%
Pressure regulation fault reducing apply pressure to element B
10%
Warped clutch steels or glazed friction discs
Diagnostic Steps
1
Consult the clutch apply chart to identify which gears use friction element B, then verify slip occurs in those gears.
2
Monitor input vs output shaft speed RPM in the affected gears to quantify the degree of slippage.
3
Check transmission fluid level (hot and cold) and condition — low or burnt fluid is the most common correctable cause.
4
Perform a line pressure test in the gears where element B is applied to verify adequate pressure.
5
If pressure is normal, the friction element is worn internally — transmission teardown and clutch pack replacement is required.
6
Check for related solenoid or pressure codes that may indicate a hydraulic cause before condemning the clutch pack.
Estimated Repair Cost
$300 - $3,500
Parts + labor, varies by vehicle and location
The TCM has detected slippage in transmission friction element B. This friction element is not fully engaging during its commanded apply state, allowing rotational speed differences across the element. This slip may be felt as RPM flaring during shifts, delayed engagement, or a general lack of power...
The most common cause of P079B (Transmission Friction Element "B" Slip Detected) is: Worn friction element B clutch pack with reduced friction material
Typical repair costs for P079B range from $300 to $3,500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Slippage in friction element B can cause unpredictable power delivery and RPM flares. The vehicle may lose drive power momentarily during acceleration. Limit driving to essential trips only and avoid highway speeds. Continued operation will worsen damage rapidly.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P079B to identify the root cause.
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Quick Info
Category
Powertrain
System
Automatic Transmission
Difficulty
Type
Generic (SAE)
Recommended Tools
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