4F85

What the Code Means

Code 4F85 indicates a gear ratio plausibility error for clutch E. The cause depends on the transmission type: on the 6HP, it's input shaft bushing wear; on the 8HP, it's a failed D drum inner seal. Clutch E is engaged in specific gears, and slip or incorrect oil pressure triggers this code.

Symptoms

• Transmission warning light comes on
• Gear slip
• Harsh shifting
• Limp mode

Diagnosis and Repair

Step 1: Identify the Transmission Type

• For the 6HP: check the input shaft bushing for wear.
• For the 8HP: check the condition of the D drum inner seal.

Step 2: Check the ATF

• Make sure the ATF level and condition are correct.

Step 3: Replace the Faulty Components

• Replace the worn parts and clear the fault codes.

Secondary Damage

Continuing to drive can cause further damage to clutch E and adjacent components, eventually leading to complete transmission failure.