• Shift timing codes for any of the controlled gear commands
  • Erratic shift feel & engagements
  • Burnt clutches


The pressure reduction valve supplies a specific constant oil pressure to the control solenoids (EDS 1, 2, 3 & 4). If wear is severe, the pressure could be too high, causing aggressive shifts and harsh feel. If the pressure drops, the result will be slipping and clutch failure.


Oversizing the bore with Sonnax tool kit restores roundness, concentricity and finish. Reassembly of valve train with Sonnax oversized PR valve and matching spring completes the restoration to OE functionality.


Required tool kit F-85755-TL9 is no longer in production. Check with your distributor for availability.


Oversized Pressure Reduction Valve Kit
Part No. 85755-09K

Also fits ZF5HP19FL and ZF5HP19FLA.

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

The pressure reduction valve in the ZF5HP19, ZF5HP19FL and ZF5HP19FLA units is designed to limit solenoid feed oil pressure. Wear in the bore and on the valve spools can cause the feed oil pressure to be high or low depending on the severity and location of the wear. Wear at the balance end contributes to high pressure and harsh shifting, while wear around the regulating and limit spools will tend to cause clutch slippage and failure. Installation of the Sonnax oversized pressure reduction valve kit 85755-09K will restore OE pressure control and limits to the solenoid feed circuits.

  • Hardcoat anodized aluminum valve combats premature wear
  • Spring is recalibrated to match OE spring calibration
  • Valve
  • Spring
  • ZF5HP19 Oversized Pressure Reduction Valve Kit 85755-09K
  • ZF5HP19 Oversized Pressure Reduction Valve Kit 85755-09K

You need this if...

Vacuum tests at the ports indicated fails to hold the recommended minimum of in-Hg

ZF5HP19 Oversized Pressure Reduction Valve Kit Vacuum Test Locations