P0796: How to Diagnose & Fix — Pressure Control Solenoid 'C' Performance or Stuck Off

The 35R clutch wave plate inside the 6T70/6T75 six-speed transaxle cracks and fractures, allowing the 35R clutch piston to overstroke and leak apply pressure. The result is a hard flare or slip in 3rd and 5th gear and eventually a complete loss of reverse. Failures typically begin after about 25,000 miles and are extremely common on the early Lambda Acadia; GM eventually extended coverage on the wave plate to 10 years/120,000 miles. Debris from the broken plate circulates through the transmission, so a simple plate swap is often not enough on high-mileage units.

Owners of the 300-series Land Cruiser and closely related TNGA-F Toyota/Lexus models have reported delayed engagement, low-speed hesitation, or abrupt 10-speed automatic shifts, especially when cold or during rolling stops. Toyota service literature for related powertrain calibration concerns points to software logic rather than hard-part failure in many cases. Complaints typically describe inconsistent throttle response paired with a sudden downshift or lurch.

Gen 5 Camaros with the 6L50/6L80/6L90 six-speed automatic commonly exhibit a 2-3 upshift 'flare' where engine RPM briefly rises before the gear engages, sometimes followed by a firm bump. GM issued bulletins calling a mild 2-3 slip/flare a 'normal characteristic,' but worsening flare typically indicates a real hydraulic leak, most often at the 3-5-Reverse clutch drum or clutch-regulator valve, and can throw pressure/ratio codes. Left unaddressed, slipping accelerates clutch wear.

P0700 is not a specific fault by itself — it is an umbrella/MIL-request code the ECM stores whenever the transmission control module (TCM) detects an internal transmission problem and asks the ECM to turn on the check-engine light. On the Silverado 1500 it almost always appears alongside more specific companion codes, and the underlying failure follows two dominant, well-documented patterns depending on the transmission. On trucks with the 6L80 six-speed automatic (many 5.3L and 6.2L V8 trucks, plus 2014-onward 4.3L V6 trucks; 2015-onward 6.2L trucks use the 8L90 eight-speed instead), the internal TEHCM (Transmission Electro-Hydraulic Control Module — GM's combined valve body, solenoids, pressure switches, and TCM in a single pan-mounted unit) develops internal circuit-board/solenoid faults from heat and fluid degradation, throwing P0700 together with codes like P0796, P0777, P0842, or P0973 and dropping the truck into limp mode. On older/base trucks with the 4L60E four-speed (2007-2013 4.3L/4.8L), the same P0700 is typically triggered by a failed shift solenoid (P0753/P0758) or a faulty internal mode switch. Because P0700 is a stored 'passenger' code, a scan tool that can talk to the TCM (not just a basic reader) is required to pull the specific sub-code that identifies the actual failed component.

First-generation Enclaves (2008-2017) use the 6T70/6T75 6-speed automatic, whose stamped-steel 35R wave plate can crack at the teeth after enough shift cycles. When it fractures, the transmission abruptly loses 3rd, 5th, and reverse gears, and debris can damage the valve body, drums, and torque converter. Failure typically occurs in higher-mileage 2008-2012 builds.