Replaces the chafed or heat-damaged internal solenoid harness inside 2006-2009 Allison LCT 1000, 2000 and 2400 units behind the 6.6L Duramax.
If your 2006-2009 Chevrolet Silverado or GMC Sierra HD with the 6.6L Duramax keeps dropping into limp mode and the solenoid codes change every time you scan it, the internal wire harness is a prime suspect. This is the harness for the Allison 1000 six-speed (also built as the 2000 and 2400 Series) that carries power and ground from the 20-pin case connector to the seven solenoids and the pressure switch on the valve body. It replaces GM 29543336 and crosses to Rostra 350-0087, Transtar 121446C, GFX 411511BDR, Natpro 35869D and WIT 116446B.
The Allison 1000 has no shift cables or vacuum modulator. Every shift, every clutch-to-clutch handoff and converter lockup is commanded by the TCM through solenoids, and on the 2006-2009 six-speed there are seven of them: PCS1, PCS2, shift solenoids SS1, SS2 and SS3, the TCC solenoid with its red connector, and the modulated main pressure (G) solenoid. All of those circuits run through this one harness, sitting in hot fluid inside the pan. The plastic jacket and wire insulation harden with heat cycles, and where the harness runs close to the case and valve body it can rub through. Once a conductor is chafed, the TCM sees an open, a short to ground or an out-of-range current, and it protects the transmission by locking a gear.
Codes that jump between unrelated solenoids point at shared wiring, not seven solenoids failing at once. Unplug the case connector and ohm each solenoid circuit through the harness. Sonnax publishes the 2006-2009 resistance values: about 5.5 ohms for PCS1, PCS2 and TCC, and about 22 ohms for SS1, SS2, SS3 and the G solenoid. An open or a reading that changes when you wiggle the harness, or a circuit showing continuity to the case, is a wiring fault. Then drop the pan and look for scuffed insulation and green or cracked connectors. Our Allison 1000 limp mode guide walks the full diagnostic order, and the valve body testing guide covers the hydraulic faults that can set similar codes.
This harness is the 2006-2009 six-speed layout used in Chevrolet and GMC 2500HD and 3500HD Duramax trucks (LBZ and LMM). Be careful about two look-alikes. The 2004-2005 five-speed also has seven solenoids, so solenoid count alone does not prove you have the six-speed. And the 2010-up valve body was fully redesigned, so later harnesses are not the same part. Transmission Digest's valve body ID article also lists GM 29543334 for the 2006-2009 harness, so check the number on your old harness against this one, or send us your year and VIN and we will confirm before it ships. You can browse everything we carry for this unit on the Allison 1000 parts page.
If the pan comes down full of clutch material, or the codes are ratio and slip codes instead of circuit codes, the harness is not your whole problem; see our Allison 1000 fluid and filter specs before you button it up.
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Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
It is listed for the 2006-2009 six-speed. The 2004-2005 five-speed also uses seven solenoids, but it is a different valve body generation, so do not assume interchange. Match the number on your old harness or send your year and VIN.
A single bad solenoid usually sets the same code every time. A chafed harness tends to set codes on different circuits, often intermittently and when hot. Ohm each circuit at the case connector and compare to the published values: roughly 5.5 ohms for PCS1, PCS2 and TCC and 22 ohms for the shift and G solenoids.
Normally no. With the pan and filter off you can unplug the solenoids and pressure switch, release the case connector and unclip the harness from its tabs. It is a pan-down job on the truck.
Use an Allison-approved fluid. Allison now recommends TES 668 across the 1000 Series, and TES 668 fluids are backward compatible with TES 295 fluids already in the unit.
Clear the stored codes and confirm each solenoid command with a scan tool. A harness swap does not change the clutches, so adaptive values usually do not need resetting unless other repairs were done at the same time.
