Replaces the two shift solenoids, the TCC lockup solenoid and the EPC pressure solenoid on 1991-2003 GM 4L80E and 4L85E valve bodies.
This is a new four-solenoid set for the early-harness GM 4L80E and its 4L85E sibling, built 1991 through 2003 with the MT-1 RPO code. Those transmissions sit behind the 5.7L, 7.4L, 8.1L and 6.5L diesel in three-quarter and one-ton Chevrolet and GMC pickups, Suburbans, Express and Savana vans and motorhome chassis. If your truck has quit upshifting, slams into every gear, or cruises the highway without converter lockup, these four parts are the ones on the valve body that control all of it. The set replaces OE 24230288 and 24230289 (shift A and B), 24210864 (TCC) and 24243101 (EPC). All four are new, not rebuilt cores.
The 4L80E has no throttle cable and no governor. Every gear change is an electrical command. Shift solenoids A and B are simple on/off valves, and the on/off combination of the pair tells the shift valves which of the four gears to hold. The TCC solenoid opens to apply the converter clutch once the truck is cruising. The EPC solenoid is different: it is a force motor that turns a varying current from the computer into line pressure, so it decides how firmly every clutch pack and the band are squeezed. That makes it the part with the most power to burn up a transmission when it drifts.
Separate circuit codes from performance codes. A circuit code means the computer sees an open, a short or wrong current, so test resistance at the case connector to find out whether it is the solenoid or the internal harness. A performance code means the solenoid clicks but the hydraulics do not follow, and that can be a worn valve body. Sonnax lists low solenoid feed pressure and repeat solenoid codes among the recurring 4L80-E complaints, and a new solenoid will not cure a worn feed valve bore. Run a line pressure test too. Our EPC solenoid symptoms guide has the pressure chart, and the shift solenoid A and B guide walks through the code tree.
Fits GM 4L80E and 4L85E transmissions from 1991 through 2003 with RPO MT-1. It does not fit the 2004-and-later units, which use a different connector and solenoid family. One more early-year detail: ATRA documents that 1991-1993 units left the factory with a silver Bosch EPC solenoid and 1994-on units with a black Holley design, and the two are not interchangeable. If your 1991-1993 truck still has its original valve body and silver force motor, send us your year and VIN before ordering. Everything else for this unit is on the 4L80E shop page.
Since all four parts live on the valve body, you pay the labor of dropping the pan once whether you change one or all four. Drain, pull the pan and filter, then change the solenoids one at a time so no plug ends up on the wrong part. Put a film of clean ATF on each O-ring and make sure it seats square in its bore. Inspect the case pass-through connector while the pan is off; Sonnax notes its plastic retention tabs commonly break, letting the connector push into the pan area and leak. If the internal wiring is brittle or the insulation is cracked, replace it with the 1994-2003 internal wiring harness now rather than chasing intermittent codes later. Refill with Dexron VI, which Pennzoil rates as back serviceable for older Dexron III units, clear codes and road test through all four gears and lockup.
If you only have a shift code and the rest of the unit is healthy, the A and B shift solenoid pair is the lower-cost option.
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Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
No. It is for 1991-2003 4L80E and 4L85E units with RPO MT-1. The 2004-and-later transmissions use a different connector and solenoid family; see the 2004-up kits on our 4L80E shop page.
Yes, the listing covers 1991-2003 4L85E units as well as the 4L80E.
Often it is the EPC circuit. When the computer sees EPC current that does not match what it commanded, it sets code 73 or P0748 and commands maximum line pressure, which makes every shift harsh. Confirm the code and the wiring before replacing parts.
ATRA notes 1991-1993 units used a silver Bosch EPC solenoid and 1994-on units a black Holley design, and they are not interchangeable. Look at your old EPC and send us your year and VIN if it is the silver early style.
Clear the codes and road test through every gear and converter lockup so the computer can see normal operation, then check the fluid level hot.
Dexron VI ATF. It is back serviceable for the Dexron III these trucks originally specified.
