GM 8L Gen. 2 Valve Bodies with TFPS Installed: Identification & Codes

Let’s take a look at the latest GM 8-speed transmission that, starting in 2023, comes equipped with a valve body that incorporates a transmission fluid pressure switch (TFPS). This valve body with the TFPS installed is officially designated by GM as a Generation 2 valve body and may be found in 8L45 and updated 8L80 units, though it has not yet been identified in any 8L90 applications. At the time of this article being published, the TFPS appears to be available only as part of a complete valve body assembly.

The purpose of the new TFPS is to monitor unit return lube pressure, which is 40 kPa (5.8 psi). Electrically, it has three wires: a 5 V reference, low reference (controller ground) and signal wire.

Determining Whether ’23-Later 8L Vehicle in the Shop has Gen. 2 Valve Body Installed

Wiring diagrams from tech resources such as ACDelco TDS^®, Shop Key-ProDemand^®, ALLDATA^®, etc. utilizing the VIN will easily identify the valve body generation. Inclusion of the pressure switch wiring in the diagram is the best method of determination I have found to date. The TFPS will be located on the valve body as shown in Figure 1. Refer to Figure 2 for vehicles that potentially have the Gen. 2 valve body installed.

Figure 1 – Transmission Fluid Pressure Switch Electrical Circuits

Figure 2 - Vehicles That Could Have Gen. 2 8L45/80 Valve Body Installed

Be aware that some of the vehicles listed may have a 10-speed transmission, and some 8-speed transmissions will use the previous design, Gen. 1 valve body. Considering accuracy, the VIN along with the wiring diagram is the best method of identification.

Observed Generational Differences

• There is a new clutch selector valve (CSV) and #4 checkball in the Gen. 2 valve body that work in conjunction with proportional control pressure (PCP) oil. The CSV is fed PCP enable oil in 6^th, 7^th and 8^th Gears through the S9 solenoid. The #4 checkball seats in 1^st through 5^th Gears, eliminating clutch oil to exhaust at the CSV.
• A lube regulator valve is not present nor shown in the available Gen. 2 valve body’s oil circuit diagrams.
• There are other physical differences in various valves and bore sizes. Pressure regulator valve and shuttle valve lengths and diameters are different. The TCC control valve diameter is also larger.
• All the clutch control solenoids are now fed with line pressure (Figure 3). This Gen. 2 unit does have an AFL valve present like in earlier valve bodies, but its job is now greatly reduced, with AFL feed oil limited to on/off S8 and S9 solenoids and several other valve body circuit variables.

Figure 3 - Gen. 1 vs. Gen. 2 8-Speed Valve Body Solenoid Supply

That’s it for now on this latest Gen. 2 8L valve body. Enjoy the data! Many thanks to Travis Ripplinger, Dave Van Setters and Shawn Stacey at Midway Transmissions.

Jim Mobley is a Sonnax technical communication specialist. He is a member of the Sonnax TASC Force (Technical Automotive Specialties Committee), a group of recognized industry technical specialists, transmission rebuilders and Sonnax Transmission Company technicians.