Transmission Friction Element Slip Detected (P079B)
The P079B code indicates that the transmission control module (TCM) has detected unexpected slip in one of the transmission's friction elements, such as a clutch or band. This slip occurs when the actual gear ratio differs from the commanded ratio, often due to worn clutches, low fluid pressure, or hydraulic circuit issues. Prolonged slip can cause overheating and severe internal damage.
01. Most Common Causes
- Low transmission fluid level or degraded fluid
- Worn or burnt clutch plates/bands
- Faulty transmission solenoid or valve body
- Internal hydraulic leak or pump failure
02. Symptoms You Will Notice
- Harsh or delayed shifting
- Transmission slipping or flaring between gears
- Check Engine Light illuminated
- Reduced fuel economy and acceleration
03. Step-by-Step Diagnosis
Step 1: Scan for codes and record freeze frame data.
Step 2: Check transmission fluid level, color, and smell for burning.
Step 3: Perform a pressure test and inspect solenoids/valve body.
Step 4: If no external issues, remove transmission for internal inspection.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
No, driving with a slipping transmission can cause catastrophic failure. Have it towed to a shop.
How much does it cost to fix?▼
Diagnosis is $50-$150. Repairs range from $200 for a fluid change to $3,000+ for a rebuild or replacement.