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Automatic Transmission

ZF9HP48, 948TE Line Pressure Control and Diagnostics

The nine-speed ZF9HP48 transmission developed by ZF and the 948TE made by Chrysler are very similar in almost every way and have some very unique characteristics and features. The units are utilized in the Acura TLX and MDX, Chrysler 200 Fiat, Honda CR-V, Jeep Cherokee KL and Renegade, Range Rover, and Land Rover, to name a few.

One unique feature is applying torque converter lockup on gears one to nine to further maximize fuel efficiency. This transmission platform is the first to use interlocking dog clutches in a passenger car. One of the unique features is how the line pressure is controlled, however.

These transmissions utilize a traditional pressure regulator valve and have an additional valve named the shift valve-system pressure valve, or SV-SP valve for short. The SV-SP valve uses the EPC pressure from the system pressure solenoid to regulate line pressure from the pump to the balance end of the pressure regulator valve.

Typically the OEM would use a valve spool on the pressure regulator valve itself for balance control. It is not entirely clear what motivated the designers to use this unique setup; instead, it can be speculated that one of the benefits is more precise control of line pressure.

ZF9HP48 & 948TE Line Pressure Control

So what does this mean to you? Take care when digging into these valve bodies and checking for wear. It has become common practice to look for wear at pressure regulator valve bores, especially the typically inboard balance spool where the primary force action occurs.

 But for this valve body, don’t overlook the SV-SP valve! It is highly active and feeds the pressure regulator valve, so wear at the SV-SP valve will affect line pressure control, shifts, and clutch durability.

Jason Larochelle is a Sonnax product support representative. He is a member of the Sonnax TASC Force (Technical Automotive Specialties Committee), a group of recognized industry technical specialists, transmission rebuilders and Sonnax technicians.

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