P079C

Code

Generic P — Powertrain

Transmission Friction Element C Slip Detected

Brand: Generic

Type: P — Powertrain

Views: UK: 21 EN: 28 RU: 25

AI status

Completed

ready

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Page language: EN

Causes

Low or incorrect transmission fluid level
Contaminated or degraded transmission fluid
Failed/weak transmission pressure control or shift solenoid
Blocked transmission fluid passages or clogged filter
Internal valve body fault or sticking valve
Worn or damaged clutch plates or friction material in Friction Element C

Symptoms

Delayed, harsh, or erratic shifts in affected gears
Loss of drive or inability to hold gear under load
Transmission slipping under acceleration or during gear changes
Diagnostic trouble code P079C stored (may be accompanied by other transmission codes)
Transmission shuddering or burning smell if friction material overheated
Check Engine or Transmission warning lamp illuminated

What to check

Retrieve freeze-frame and all stored transmission-related codes with a scan tool
Inspect transmission fluid level and condition (color, odor, particles) with warm engine, on level ground
Scan live PIDs: transmission fluid temp, commanded clutch state, solenoid commanded duty/current, turbine/input and output speed, calculated slip ratio
Check for related codes (solenoids, line pressure, speed sensors)
Visually inspect wiring and connectors for the solenoid(s) and TCM for damage, corrosion, or poor connections
Perform a basic pressure check (static/line pressure) if factory procedures available

Signal parameters

Transmission fluid temperature (°C/°F)
Line pressure (kPa/psi) or requested vs actual pressure
Commanded and actual clutch engagement state for Friction Element C
Shift/pressure control solenoid commanded duty cycle (%) and current (A)
Turbine (input) speed (rpm)
Output speed (vehicle speed sensor) (rpm)

Diagnostic algorithm

Read and record P079C and any related codes and freeze-frame data with a professional scan tool.
Verify vehicle symptoms via road test while monitoring live PIDs (line pressure, solenoid commands, input/output speeds, slip).
Check transmission fluid level and condition; correct level and replace fluid/filter if contaminated or burnt. Re-test.
Inspect wiring and connectors for the solenoid circuit; repair any damage and verify proper connector seating. Clear codes and retest.
Measure solenoid resistance and compare to specification. Command the solenoid with a scan tool to confirm operation and observe pressure/clutch response.
If electrical checks pass, perform a hydraulic/line pressure test per factory procedure to confirm pressure delivery to Friction Element C circuit.
If pressure is low or intermittent, inspect/repair valve body (sticking spools, bore wear), replace valve body components or replace solenoid as required.
If hydraulic pressure is correct but slip persists, remove and inspect clutch pack/drum/piston for wear or damage; replace worn friction plates or rebuild transmission as needed.
After repairs, clear codes and perform road test with data logging to confirm the fault is resolved. If unresolved, consult vehicle-specific service manual and TCM software updates or reprogramming procedures.

Likely causes

Low fluid level or degraded fluid reducing line pressure
Faulty pressure-control or shift solenoid controlling Friction Element C
Valve body spool or bore wear causing pressure loss to that circuit
Worn clutch pack or ruptured friction material in the C element
Open/short/poor connection in solenoid wiring or connector
Contamination blocking valve ports or filter

Fault status

⚠️ Status

TCM detected excessive slip of Transmission Friction Element C — the clutch is not transferring expected torque. Possible causes include low hydraulic pressure, faulty solenoid/valve body, internal leakage, or worn clutch pack. Further diagnosis required.

🔴 Repair difficulty: Hard

⏱️ Diagnostic time: 2.0-6.0 hours