Internal harness with the lock-up TCC solenoid for 2003-2006 GM 4L60E. Fixes TCC and shift solenoid circuit faults caused by cracked wires or a dead solenoid.
A 2003-2006 Silverado 1500, Sierra 1500, Tahoe, Yukon, Suburban or Avalanche whose 4L60E loses converter lockup when it gets hot, sets P0740 or P0742, or throws a handful of unrelated solenoid codes on the same drive is a classic candidate for a new internal harness. This assembly is the 2003-and-later style harness, crossing to 350-0061, with the on/off TCC solenoid already molded onto it. It is the harness alone, so it suits a truck whose solenoids are newer or already tested good, and it costs less than buying a full solenoid kit when the wiring is the actual fault.
For 2003 GM moved to a revised internal harness. It still enters the case through the round pass-through connector, but its routing, branch lengths and TCC solenoid differ from the early version. From the connector it feeds the 1-2 and 2-3 shift solenoids, the 3-2 control solenoid, the pressure control solenoid, the TCC PWM solenoid and the pressure switch manifold, which also carries the fluid temperature sensor. The on/off TCC solenoid is part of the harness itself. All of these solenoids work off the same regulated actuator feed oil, roughly 115 psi according to Sonnax, so the hydraulic side is common to them and the harness is the only thing that tells each one when to act. One rubbed-through wire can take out lockup, a shift or line pressure control depending on which branch it is.
ATRA's bulletin on 4L60E and 4L80E limp mode with solenoid codes points to wiring and connector problems as the most likely cause, so start there. Inspect the case connector for fluid that has wicked up the harness, check the vehicle-side wiring back to the PCM, then measure each circuit from outside while flexing the connector. Our P0785 and limp mode guide explains why multi-code failures so often turn out to be wiring, and the P0740 diagnosis guide covers the converter clutch circuit by itself. If the codes point at line pressure instead, read the P0748 pressure control guide first.
Listed for the 2003-2006 GM 4L60E, and also used in 4L65E and 4L70E units built with the 2003-up harness. It will not install in a 1993-2002 transmission; those take the earlier 350-0025 harness. GM kept refining this family through the later 2000s, so compare the connector shapes, branch layout and TCC solenoid in the photos with the harness in your pan, or send us the year and VIN and we will confirm. The rest of our electrical and hard parts are on the 4L60E parts page.
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Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
GM redesigned the internal harness and TCC solenoid for 2003. The routing and TCC solenoid differ, so the early and late harnesses do not interchange.
4L65E and 4L70E units built with the 2003-up style harness use the same design. Compare the connectors and layout to your existing harness before installing.
No. This is the harness with the on/off TCC solenoid attached. The shift, 3-2, pressure control and TCC PWM solenoids plug into it and are sold separately or as a kit.
The solenoids share a power feed and the same harness, so one damaged wire or terminal can set codes for several of them. That is why the harness is worth checking before buying solenoids.
A filter, a pan gasket and Dexron VI fluid. Clear codes after the case connector is plugged back in, since disconnecting it sets codes of its own.
