Transmission Friction Element Slip Detected
The P079C code indicates that the powertrain control module (PCM) has detected unexpected slip in a transmission friction element, such as a clutch or band. This slip occurs when the actual gear ratio differs from the commanded ratio, often due to worn friction material, low fluid pressure, or hydraulic circuit issues. Prolonged slip can cause overheating and internal damage.
1. Symptoms You Will Notice
- Hesitation or delayed engagement when shifting
- Transmission slipping or flaring between gears
- Check Engine Light illuminated
- Burning smell from transmission fluid
2. Most Common Causes
- Excessive wear of friction element 'C' (clutch discs, plates, or band)
- Hydraulic pressure leak in the circuit for element 'C'
- Faulty or stuck transmission control solenoid
- Worn or damaged valve body control valve
- Improper transmission fluid level or condition (low, contaminated, wrong type)
- Leaking seals or O-rings on the friction element
- Faulty transmission input or output speed sensor
- Internal mechanical transmission issues (pump, relief valve)
- Outdated or corrupted TCM software
3. Step-by-Step Diagnosis
Step 1: Check transmission fluid level and condition; top off or replace if necessary.
Step 2: Scan for additional codes and perform a transmission pressure test.
Step 3: Inspect wiring and connectors to transmission solenoids and sensors.
Step 4: Perform a clutch/band apply test using a scan tool to identify the slipping element.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
No, continued driving can cause severe internal damage. Have the vehicle towed to a shop.
How much does it cost to fix?▼
Diagnosis typically costs $50-$150. Repairs range from a simple fluid change ($100-$250) to a full rebuild ($1,500-$4,000).
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.