Installs the pressure switch discs and seals on GM 6L45/6L50/6L80/6L90/6T70/6T75 valve bodies to fix rough 1-2 shifts without swapping the whole TEHCM.
If your Silverado, Sierra, Tahoe, Yukon, Escalade or heavy-duty 6L90 truck bangs into second, flares on the 2-3, or sets a fluid pressure switch circuit code such as P0842 or P0843, the problem may live in a part the size of a shirt button. The pressure switches built into the GM six-speed control module are sealed by tiny laminate discs and rubber seals, and when those wear out the computer stops getting a true pressure signal. This 124740-TL30 style kit is the set of four hand tools that lets you replace those discs and seals cleanly, and it includes five seals and five discs so you can finish one module without a second order.
The 6L80 and 6L90 use a TEHCM, a combined control computer and solenoid body that bolts to the valve body. Built into it is a row of pressure switches, each fed by a clutch apply circuit. Oil pressure pushes on a thin laminate disc, the disc moves the switch contact, and the computer uses that signal to confirm a clutch actually applied and to learn how fast it did. The discs and seals are small and soft, and trying to seat them with a screwdriver or a pick almost always folds a disc edge or rolls a seal lip. The four tools in this kit solve that one job:
Not every harsh shift is a switch. Start with fluid level and condition, then read switch status on a scan tool while you drive and see which switch is late or stuck. Our 6L80 P0842 fluid pressure switch guide walks through the circuit checks, and the 6L80 common problems and fixes guide covers the other failures, such as a worn valve body bore or a weak pump, that cause similar shifts. If line pressure itself is low, new discs will not cure it.
The listing covers the GM 6L45, 6L50, 6L80 and 6L90 rear-drive units and the first-generation 6T70 and 6T75 front-drive units, and it is meant for use with the F 124740-30K seal and disc service pack. Manufacturer part number B-124740. The 6L90 is the heavy-duty version found in 2500 and 3500 trucks and vans, and it shares the same module design, so the kit handles both. Second-generation 6T70 modules changed, so confirm a Gen 1 module before ordering for a front-drive vehicle. If you are not sure what your truck has, send us the year and VIN, or browse our 6L80 transmission parts page.
Disconnect the battery and drop the pan, then remove the valve body with the TEHCM attached. Separate the module on a clean bench, pick out the old discs and seals, and inspect each bore for scoring. Seat the pusher piston, place a new laminate disc and work the laminate tool all the way around, then lubricate the seal with Dexron VI and press it in with the plunger and installer. Do every switch on the module, not only the one that set a code. Reassemble, torque the valve body bolts in the factory sequence, and refill with Dexron VI using a GM ATF filler adapter, since these units have no dipstick. Set the level hot on the check plug, reset adapts, and drive a relearn. If the bores are worn or the module board has failed, a 6L80 valve body with solenoids is the better fix.
| Fits | GM 6L45, 6L50, 6L80, 6L90, 6T70 (Gen 1), 6T75 (Gen 1) |
| Kit contents | Pusher piston, seal plunger, seal installer, laminate installation tool, 5 seals, 5 laminate discs |
| Rebuilds | One TEHCM pressure switch assembly |
| Interchange | Works with F 124740-30K service pack |
| Manufacturer part number | B-124740 |
Yes. The 6L90 uses the same style of TEHCM pressure switches as the 6L80, and the kit is listed for the 6L45, 6L50, 6L80 and 6L90 plus Gen 1 6T70 and 6T75 units.
The kit includes five rubber seals and five laminate discs, which is enough to rebuild the switches on one module. The four tools are reusable for more modules with a refill pack.
Fluid pressure switch circuit codes such as P0842 and P0843 are the most direct match. It can also stop harsh shifts and failsafe events caused by a bad switch signal. It will not fix a failed solenoid or a damaged circuit board.
Dexron VI. Fill through the case fill point and set the level at operating temperature on the check plug with the engine running.
No programming is needed because the calibration does not change. Reset transmission adapts with a scan tool and drive the truck through a relearn so shift timing is learned again.
