P079D: Transmission Friction Element D Slip Detected

What it means

Same condition as element A slip, applied to friction element D (fourth clutch or band).

At a glance

• Usually lights the check-engine light

How it works

The transmission control module compares input and output speed with the commanded gear to check whether friction element D is holding. It sets P079D when element D, which may be a clutch or band depending on the transmission, slips more than expected while applied.

Common causes

Most likely first.

1. Worn or damaged friction element D
2. Low or degraded transmission fluid
3. Hydraulic pressure loss or internal leakage
4. Valve body or control fault affecting element application

Symptoms

• Check engine or transmission warning light on
• Harsh, delayed, or missing shifts
• Possible limp mode (locked in one gear)
• Slipping or shuddering during gear changes

How to diagnose it

1. Save the freeze-frame data and check transmission live data for the gear command and input/output speeds when the slip occurred.
2. Check the transmission fluid level and condition using the vehicle maker’s specified procedure, since low or degraded fluid can reduce the pressure that holds element D.
3. Inspect the transmission wiring and connectors for damage, corrosion, or loose connections that could affect element D control.
4. Compare commanded and actual gear ratios during a controlled road test to confirm when element D slips and whether the problem occurs hot, cold, or under load.
5. If fluid and external wiring checks are satisfactory, have hydraulic pressure and valve-body operation checked against the manufacturer's specification.
6. If pressure control is sound but element D continues to slip, inspect the internal clutch or band and its seals for wear or damage.

Common fixes

• Correct the transmission fluid level or replace fluid that is degraded, using the specified fluid and procedure.
• Repair damaged wiring or clean and secure affected connectors.
• Repair a leaking hydraulic circuit or faulty valve-body component affecting element D.
• Replace worn element D friction parts or damaged apply seals.

Can I keep driving?

Avoid towing, hard acceleration, and long trips while the transmission is slipping; continued driving can overheat the fluid and damage internal parts. If shifts are missing, severe, or the vehicle enters limp mode, stop somewhere safe and arrange recovery.