|Code||Fault Location||Probable Cause|
|P0777|| Pressure control solenoid B -stuck on |
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|Wiring, pressure control solenoid|
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What Does Code P0777 Mean?
Automatic transmissions, whether conventional or continuously variable transmissions (CVT), use fluid pressure to actuate changes inside the transmission. This can be anything from initiating gear changes to torque converter lockup or just softening shift points for a smooth drive. The line pressures that control these functions are metered by pressure control solenoids.
Pressure control solenoid B performs some of these functions in your automatic transmission. Depending on the vehicle design, pressure control solenoid B assists in shift controls in higher gear ranges, performs torque converter lockup duties, or both. It does so by regulating fluid pressure to the internal drum bands and friction plate clutches.
Pressure control solenoids are electronically controlled through the powertrain control module or transmission control module. When the circuit is energized, pressure control solenoid B allows actuation of other transmission controls via fluid pressure. For example, on the GMC Acadia, actuating pressure control solenoid B allows actuation of the clutch boost valve and the clutch regulator valve.
When DTC P0777 is present, it indicates that pressure control solenoid B is stuck in the open position and the Check Engine light is illuminated.
What are the common causes of code P0777 ?
- lack of transmission fluid maintenance
- internal transmission control module short
- pressure control solenoid B failure
- dirt or obstruction in pressure control solenoid passage
What are the symptoms of code P0777 ?
With DTC P0777, there may be no discernable symptoms present other than a Check Engine light illuminated. The CEL could also be accompanied by one or more of the following:
- harsh gear engagement
- slipping transmission
- transmission flares while driving
- burnt transmission fluid
- limp mode
- transmission won’t engage drive
How do you troubleshoot code P0777 ?
Transmission pressure control solenoid problems are often misdiagnosed by cutting corners. In many instances, transmissions have been replaced or overhauled when a simple pressure control solenoid replacement would have corrected the condition at a much lower cost.
To diagnose DTC 0777, you’ll require a pair of leads to the battery or a 12V tester. You will also need a wiring schematic for your particular vehicle model which you can obtain from many parts retailers at no cost. You might need basic hand tools for component removal and inspection.
Pressure Control Solenoid diagnosis
Locate pressure control solenoid B on your transmission. The sensor is usually protected either by being mounted on the top or the side of the transmission. Disconnect the electrical connector from the pressure control solenoid.
Connect one lead between the battery’s negative terminal and the ground terminal on the solenoid connector. Connect another lead to your battery’s positive terminal and connect the lead the control circuit on the solenoid, listening for an audible click. Disconnect the positive lead and reconnect several times to ensure the click is consistent. If no click is heard, replace pressure control solenoid B.
Pressure Control Solenoid circuit inspection
If pressure control solenoid B clicks when powered up, ensure the circuit to the solenoid is proper. Because DTC P0777 indicates the solenoid is stuck on or energized, you need to check for a short to voltage on the control circuit.
Test the circuit with the key in the on position with the engine off. Using a 12V test light, connect to the negative battery terminal and probe the control circuit terminal on the wiring side of the connector. If the test light illuminates, there is voltage when there should not be. Trace the circuit back to the corresponding control module (TCM or PCM). Repair any sections of wire that are damaged and may be crossed with a voltage source and retest.
Control Module Issue
If power is still present when it should not be, the powertrain or transmission control module is at fault. Replace with a known good module and retest.
Physical Blockage in solenoid
If the electrical part of the pressure control system passes diagnosis, the problem may be an obstruction in the solenoid. Disconnect the electrical connectors and remove the pressure control solenoid from the transmission. Use care to prevent dirt and debris from entering the opening in the transmission. Test the solenoid once again, observing the solenoid operation if possible. If the solenoid clicks yet the position does not change, replace the solenoid with a new one.
Check for blockages in the passages in the solenoid. A small piece of dirt can block the solenoid from fully closing. If you can visibly see an obstruction, clear it gently. Re-install the pressure control solenoid and retest.
Clear the DTCs and road test, ensuring the transmission gets to full operating temperature. Accelerate and decelerate so the transmission goes through all the gear changes. If DTC P0777 resets, replace pressure control solenoid B.