4L70E Internal Wiring Harness 2006, new and ready to install. Fits the 4L70E. Ships fast from the USA.
If your 2006-or-later Silverado, Sierra, Tahoe, Yukon, Escalade or Trailblazer SS with the 4L70E is throwing input speed sensor codes, refusing to lock up the converter or dropping into a single gear, the internal wiring harness is one of the first things worth suspecting. This is the later-style harness, interchange number 350-0078 (also listed as 77995C) and cross-referenced to GM 24234121. It is built for the 2006-on 4L65E and 4L70E with the input speed sensor mounted on the pump, and it comes with the TCC lock-up solenoid already attached.
Everything electrical inside the case runs through this one assembly. It takes the signals from the case connector on the side of the transmission and carries them to the shift solenoids, the pressure control solenoid, the TCC solenoids and the pressure switch assembly on the valve body. On the 4L70E it also handles the input speed sensor lead that runs to the back of the pump, which is the big change from earlier 4L60E-style harnesses. The computer compares input speed to output speed to judge clutch slip, so if that circuit opens or shorts, it loses its picture of what the transmission is doing and starts protecting itself.
Transmission Digest documents a known 4L70E failure where the input speed sensor wiring is not clipped into its brackets on the back of the pump and the spinning reverse input drum cuts through it, setting P0716 or P0717. A fresh harness routed correctly fixes that for good.
Pull the codes and note whether several unrelated solenoid circuits are failing together; that points at the harness or connector rather than one bad solenoid. Wiggle-test the case connector with the engine running while watching live data. With the pan off, check the harness for chafed spots near the drum and check resistance from the case connector to each solenoid. Rule out the TCM side too: the same article notes the ISS ground can be lost inside the TCM, which is fixed with an external ground rather than a new harness. If the problem is pressure-related rather than electrical, read our pressure control solenoid guide first, and the 4L70E common problems guide covers the rest.
This harness is listed for 2006-and-later 4L65E and 4L70E transmissions that have the input speed sensor on the pump. That covers the 4L70E in full-size GM trucks and SUVs from 2006 on. Earlier 4L60E and 4L65E units without the pump-mounted sensor use a different harness, which we carry as the 2003-2006 internal harness. The quickest check is to look at the back of your pump: if there is a speed sensor bolted to it, this is your harness. When in doubt, compare your old part number or send us the year and VIN. Every part for this unit is on the 4L70E parts page.
The harness is serviced with the pan and filter off. Unplug each solenoid and the pressure switch, remove the TCC solenoid bolts, and push the case connector out from inside. Route the new harness exactly like the original and clip the input speed sensor lead into every bracket on the pump so it cannot touch the reverse input drum. Make sure the speed sensor has its O-ring and retaining bolt, since a missing one lets fluid push out of the vent. Replace the case connector O-ring, refill with Dexron VI, and clear codes. If the pressure control solenoid is original, this is a good time to swap it with a 4L70E pressure control solenoid, and if the pump is suspect while you are at the speed sensor, the 2006 4L70E pump is the matching unit.
| Fits | 4L70E 2006 |
| Part type | Internal Wiring Harness |
| Condition | New |
| Brand | GM |
| Ships | From the USA |
| Warranty | 1-year |
Yes. It comes with the torque converter clutch lock-up solenoid attached, so you do not need to buy one separately.
Probably not. This version is for 2006-and-later 4L65E and 4L70E units with the input speed sensor on the pump. Earlier units without that sensor use the 2003-2006 harness we also carry.
Yes. A chafed input speed sensor lead behind the pump is a documented cause on the 4L70E. Check for a lost TCM ground and a missing sensor O-ring or bolt as well.
No. It is replaced with the pan and filter removed. You only need to pull the unit if the speed sensor lead or pump area needs work you cannot reach.
GM specifies Dexron VI for the 4L70E. Fill to level and check it hot after the repair.
