P0777 on Chevrolet: How to Diagnose & Fix

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 (2007-onward 5.3L and 6.2L V8 models), 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 (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.

Gen 5 Camaros with the 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.

First-generation Traverse models built with the 6T70/6T75 six-speed front-drive automatic use a 3-5-R clutch cushion (wave) plate that on early production was improperly heat treated and left too brittle. Repeated compression cycles during 2-3 and 4-5 shifts crack the plate; once it fractures, the vehicle loses 3rd, 5th and reverse, and the debris migrates through the transmission, plugging the filter and scoring other components so what began as one $50 plate becomes a full rebuild. GM acknowledged the condition with Special Coverage Adjustment #14404, extending coverage to 10 years/120,000 miles for affected build ranges. Owners on Traverse Forum describe the classic progression: a late or flared 2-3 shift for weeks, then an abrupt no-reverse.

Equinox models with the GM 6T70/6T75 six-speed automatic suffer shudder, harsh or delayed shifts, slipping, and loss of reverse. A common root cause is failure of the 3-5-reverse wave plate, which can crack and cause extreme shudder when reverse is engaged and eventual loss of drive. Overheated/degraded fluid that loses viscosity accelerates internal wear. Failures typically appear between roughly 60,000 and 150,000 miles. Owners report bucking when engaging gear, failure to shift out of 2nd, and inability to engage reverse.