Four-solenoid 4L80E/4L85E kit with a new internal wiring harness, pan filter and pan gasket, for curing shift, EPC and TCC solenoid codes in one service.
When a heavy-duty GM truck or van with the 4L80E or 4L85E (RPO MT1) starts throwing a mix of shift solenoid, pressure control and converter clutch codes, chasing one part at a time gets expensive. This kit replaces all four solenoids and the wiring that feeds them: the EPC pressure control solenoid, shift solenoids A and B, the TCC PWM solenoid, a new internal harness with the round case connector, a deep pan filter and a pan gasket. It is aimed at P0751 and P0756 shift solenoid performance codes, P0748 EPC faults, firm or slipping shifts and a converter that will not lock or release.
Shift solenoids A and B are simple on/off valves; the computer switches them in pairs to put the shift valves in the position for each gear. The EPC solenoid is the one that controls line pressure. It is fed by the actuator feed limit (AFL) valve, which Sonnax describes as the regulated supply to the solenoids, and the computer varies its current to raise or lower pressure. The TCC PWM solenoid is pulsed rather than switched, which lets the computer ramp the converter clutch on smoothly. The harness carries all of those signals to the gray pass-through connector in the case.
Separate electrical faults from hydraulic ones first. P0748 is an electrical code, so a resistance check of the EPC through the case connector and at the solenoid usually settles it. P0751 and P0756 are performance codes, and they can set with healthy solenoids. Sonnax documents that the EPC solenoid's constant modulation wears the AFL valve bore, and a worn AFL drops solenoid feed pressure and line pressure. If line pressure checks low with the gauge, a solenoid kit alone will not cure it. Our EPC solenoid guide gives the pressure test, and the 4L80E common problems guide helps rule out worn clutches.
Listed for the GM 4L80E and 4L85E (MT1), with cross references GM 24210864, 24248892, 24230288, 24230289 and 24200161. The harness in the photos has the later gray case connector. GM changed the 4L80E harness and EPC plug over its production run, and Sonnax sells an adapter specifically for fitting an early ('92-'02) EPC solenoid into a late ('03-later) unit, so the two styles do not plug straight into each other. Pull up the numbers on your old harness and EPC solenoid and compare them with the list above, or send us the year and VIN and we will confirm fitment. Every other part for this unit is on the 4L80E collection page.
Drain the deep pan and remove it, then pull the filter straight down and confirm its seal came out with it. Unplug the harness at the pass-through and each solenoid and unclip it from the valve body. Remove the A and B solenoids with their brackets, then the EPC and TCC PWM solenoids. Coat every new O-ring in clean ATF, seat each solenoid squarely, and lay the harness exactly where the old one ran. Check the case connector's retention tabs while you are there. Install the new filter and gasket, torque the pan bolts evenly in a cross pattern, refill with Dexron VI, and check the level hot. Clear codes and drive through every gear and a lockup.
If the pressure test pointed at the valve body, the 4L80E valve body is the next step, and towing trucks benefit from the 4L80E shift kit installed on the same service.
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Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
MT1 is GM's regular production option code for the 4L80E. It is printed on the service parts sticker in the glovebox or door, which is a quick way to confirm which transmission your truck has.
P0748 is an electrical fault in the pressure control solenoid circuit. P0756 is a performance fault, meaning shift solenoid B was commanded but the gear did not change as expected, which can be the solenoid or low feed pressure from a worn valve body.
The harness shown has the later gray case connector, and the early and late EPC plugs differ. Compare your old harness and EPC numbers with the cross references, or send us the VIN and we will check.
Yes. The kit includes a deep pan filter and a pan gasket along with the four solenoids and the internal harness.
Dexron VI, which meets GM's current specification and is approved for older Dexron III applications. Set the level hot with the engine idling.
