4L60E Internal Wiring Harness with TCC Solenoid 2003-2006

This is the internal wiring harness for 2003-2006 GM 4L60E transmissions, sold as one assembly with the lock-up torque converter clutch (TCC) solenoid attached. It crosses to OE reference 350-0061. The harness runs from the round pass-through connector in the case to the shift solenoids, EPC solenoid and pressure switch manifold on the valve body. Confirm your unit is a 2003 or later. The 1993-2002 harness (350-0025) is routed differently and uses a different TCC solenoid, so the two do not interchange.

After years in hot fluid the insulation gets brittle and cracks, wires rub through where they cross the valve body, and the case connector pins corrode or wick fluid. The TCC solenoid also fails on its own. Typical symptoms: the converter will not lock up or drops out at highway speed, cruise RPM runs high, TCC codes such as P0740, P0742 or P0743 set, or shift solenoid circuit codes come and go. Since the TCC solenoid comes on the harness, replacing both together saves chasing one broken wire.

Check the outside first. Unplug the case connector and look for fluid or green corrosion on the pins, and inspect the wiring back to the PCM. If that is clean and the codes stay, go inside.

To replace it, drain and drop the pan and pull the filter. Unplug the harness from each solenoid and the pressure switch manifold, remove the TCC solenoid bolts, squeeze the tabs on the case connector and push it into the case. Route the new harness exactly like the old one, keep it clear of the manual valve linkage, snap the connector through the case and bolt the TCC solenoid down. Install a new filter and pan gasket, refill with Dexron VI, and clear codes before the road test.