P0777 code definition
A P0777 trouble code signifies that the Powertrain Control Module (PCM) has detected a fault in one of the electronic pressure control solenoids or solenoid circuits. The hydraulic pressure regulated by the pressure control solenoids provides shift actuation for the automatic transmission and locks the torque converter into place when needed. Related codes include P0775, P0776, P0778, and P0779.
What the P0777 code means
Utilizing calculations based on the position of the throttle, the amount of load on the engine, and engine and vehicle speed help in determining how much pump pressure is needed for the vehicle to operate efficiently. When the amount of pressure desired does not match up with the actual amount produced, the PCM stores a P0777 code and illuminates the Check Engine Light. Keep in mind that some model of vehicles might require multiple failures in order for a Check Engine Light to be illuminated.
What causes the P0777 code?
Some common causes of a P0777 trouble code include failure of the electronic pressure control solenoid, blockage in the hydraulics inside of the transmission, transmission failure, dirty or low fluid, and a faulty PCM or Transmission Control Module (TCM).
What are the symptoms of the P0777 code?
Symptoms of a P0777 trouble code range from none at all to problems shifting, or even a failure on the part of the torque converter. In some cases, when this trouble code is stored, the PCM places the transmission into Limp-in mode. Some other common symptoms of a P0777 code include slipping, overheating, shifting problems with the transmission, and a decrease in the vehicle's fuel mileage.
How does a mechanic diagnose the P0777 code?
To diagnose a P0777 trouble code, the mechanic needs an advanced scanner, a hydraulic pressure diagram for the vehicle in question, and a digital volt/ohmmeter. Once the necessary tools are gathered, the mechanic should perform the following steps when diagnosing the code:
Start by checking the transmission level and condition.
Keep in mind that fluid which smells burnt or has an abnormal odor might indicate extensive damage to the transmission.
In this case, the mechanic should drop the transmission pan to see if any debris from the transmission is evident.
If no debris is detected, the mechanic should fill the transmission fluid to an appropriate level to find and fix any leaks.
*Once all leaks have been fixed, fill the transmission fluid to its normal level and start the vehicle, allowing it to reach a normal operating temperature.
Clear the code and test the system to see if the code returns. You can also download any freeze frame or stored codes at this time.
If the code returns, use a hydraulic pressure diagram to check the pressure created in the transmission. Compare your findings to the manufacturer's specifications.
Clear the code and test the system to see if it returns. If it does return, use the digital volt/ohmmeter to check the reference voltage and ground signals at the electronic pressure control solenoid producing the trouble code.
If the reference voltage or ground circuits test as open, use the volt/ohmmeter to check for continuity.
Retest the system by attempting to manually activate the electronic pressure control solenoid suing the volt/ohmmeter.
Test the PCM if no other problems are evident and the code persists.
Clear the code and test the system to see if the code returns.
Common mistakes when diagnosing the P0777 code
A common mistake made by mechanics when diagnosing a P0777 trouble code is to overlook faulty wiring and electronic pressure solenoids, and instead replacing a high pressure pump when it's not needed. This usually results in the return of the code.
How serious is the P0777 code?
While a vehicle that has a P0777 problem might not exhibit any outward problems, left unfixed, this code can result in problems with the transmission of the vehicle. Most often this materializes as problems shifting, up to and including failure of the torque converter. You can also expect to see a reduction in the vehicle's fuel mileage until the trouble code is fixed. A low fluid condition, if left unchecked, can result in damage to the transmission and require the mechanic to have to rebuild it.
What repairs can fix the P0777 code?
To repair a P0777 trouble code, the mechanic should perform the following steps:
Repair any leaks detected.
If the transmission has been damaged due to a low fluid condition, repair or rebuild the transmission, followed by a fluid flush and replacement. Then install a new torque converter before proceeding.
Replace any burnt or otherwise damaged wiring, connectors, or components.
Repair or replace the hydraulic pump. Replacement of the pump requires the mechanic to remove the transmission and partially disassemble it.
Replace the electronic pressure control solenoid if faulty.
Replace the PCM if found to be at fault.
Need help with a P0777 code?
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