Allison transmission valve body failure and limp mode
POWER TRAIN, POWER TRAIN:AUTOMATIC TRANSMISSION:FLUID/LUBRICANT:VALVES/VALVE BODY
18 NHTSA complaints · 2023-06 → 2026-07
“2024 GMC DENALI HD with approx. 12, 500 miles: The truck is constantly going into limp mode. Driving down the road, first it feels like the wheels lock up with a loud noise. Immediately goes into limp mode and check engine light comes on. Took it to the dealer yesterday 6/3/25…”
“Code P0777 – "Pressure Control Solenoid 'B' Stuck On" – Reduced Propulsion / Reduced Engine Power Initiated While merging onto the interstate, this code triggered a reduction in engine power, limiting my speed to 35 mph on a highway with a posted limit between 40-70 mph.”