Circuit/System Testing

WARNING: This page is about a different car, the 2010 GMC Sierra, 2010 GMC Cab & Chassis Sierra, 2010 Chevrolet Silverado, and 2010 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

NOTE: You must perform the Circuit/System Verification first.

Perform the Line Pressure Check . Verify the transmission line pressures are within the specified ranges.
- If not within the specified ranges, refer to Fluid Pressure High or Low .
Ignition OFF, remove the control solenoid valve assembly. Refer to Control Solenoid Valve and Transmission Control Module Assembly Replacement .
Perform the Control Solenoid Valve and Transmission Control Module Assembly Solenoid Performance Test . Test all solenoids on the Q8 control solenoid valve assembly. A pressure change should occur for each solenoid valve.
- If the Q8 control solenoid valve assembly does not pass the performance test, replace the Q8 control solenoid valve assembly.
Listed in the chart below, are conditions for each component that could set DTC P0776 or P0777. Carefully inspect each component for that condition. Repair or replace as necessary.

DTC	Component	Condition
P0776	Control Valve Upper Body Assembly (304)	3-5-R Regulator Valve (336) stuck / sticking - debris, binding, damaged valve, or scored bore
P0777	Control Valve Upper Body Assembly (304)	B-2-6 Regulator Valve (334) stuck / sticking - debris, binding, damaged valve, or scored bore
P0776 P0777	Q8 Control Solenoid Valve Assembly (314)	O-ring seals leaking Valve body filter plate assembly cracked, blocked or damaged gasket seal
P0776 P0777	Control Valve Upper Body Assembly (304)	Actuator feed limit circuit supply fluid to solenoids restricted or not available (debris or sediment blockage) B-R-1 / 4-5-6 clutch regulator valve (327) not in the applied position - debris, binding, damaged valve, or scored bore 4-5-6 clutch boost valve (329) not exhausting - debris, binding, damaged valve, or scored bore
P0776 P0777	Torque Converter (w/Fluid Pump) Housing Assembly (2)	Fluid pump housing vanes / rotor / slide damaged / scored
P0776 P0777	A/Trans Fluid Pump Cover Assembly (219)	Isolator valve (236) stuck / sticking - debris, binding, damaged valve, or scored bore
P0776	1-2-3-4 and 3-5-R Clutch Housing Assembly (51)	3-5-R clutch backing plate retaining ring (400) not seated
P0776 P0777	1-2-3-4 and 3-5-R Clutch Housing Assembly (51)	1-2-3-4 clutch backing plate retaining ring (429) not seated, causing clutch pack / piston over travel
P0776	4-5-6 Hub / Shaft Assembly (58)	4-5-6 Hub / Shaft - broken hub weld