• Soft shifts
  • High line pressure in Reverse
  • Low line rise in Drive


These problems can be caused by severe wear of the boost valve sleeve, allowing EPC and/or reverse oil leakage.


Install the Sonnax boost valve and sleeve kit which has upgraded materials, restores correct hydraulic clearances and is designed to prevent wear.

A4CF1, A4CF2

Boost Valve Kit
Part No. 84741-01K

You need this if... View Instructions Find a Distributor

Hyundai/Kia vehicles with A4CF1, A4CF2 transmissions may exhibit insufficient line rise in the drive ranges and excessively high pressures in reverse. This may be caused by continuous oscillation of the boost valve within the sleeve, creating excessive wear and a path for EPC and reverse pressures to leak. The Sonnax boost valve kit 84741-01K has upgraded wear-resistant materials and minimal clearance to prevent wear and restore proper hydraulic control. The two-spool lands have also been designed to provide more sealing engagement with the sleeve and annular grooves are added to hydraulically center the valve within the sleeve.

  • The boost valve kit eliminates wear with minimal clearance, has greater sealing integrity and annular grooves to hydraulically center
  • The boost valve kit is made from wear-resistant materials for durability
  • Valve
  • Sleeve

Sonnax valve body layouts provide a detailed overview of individual units making it quick and easy to determine what’s available for the specific valve body you’re working on. See all Sonnax valve body layouts.

Hyundai/Kia A4CF1/2 Valve Body Layout

Hyundai/Kia A4CF1/2 Valve Body Layout
  • A4CF1, A4CF2 Boost Valve Kit 84741-01K
  • A4CF1, A4CF2 Boost Valve Kit 84741-01K

You need this if...

A vacuum test at the ports indicated holds 18 in-Hg or more. If poor vacuum results are discovered at the OE pressure regulator valve, Sonnax PR valve kit [84741-03K] should be installed.

A4CF1, A4CF2 Boost Valve Kit Vacuum Test Locations