What the P0764 code means
A P0746 code indicates a problem with a shift solenoid and voltage readings that are out of parameters.
What causes a P0764 code?
Since the mid 1980s, virtually every vehicle has been designed with a computer controlled automatic transmission. The computer governs shift points and gear selection by managing the transfer of automatic transmission fluid (ATF) in the unit’s internal passages and hydraulic circuits. Shift solenoids are used to actuate these functions.
The powertrain control module (PCM) relies on sensors for information on throttle position, engine load, engine RPMs and vehicle speed to determine the proper gear ratio. In an instance where the proper gear ratio doesn’t match the gear ratio detected by the PCM, a code will be registered and the PCM may light the malfunction indicator lamp (MIL). Some vehicles require several failure cycles before the MIL will be lit.
Causes, then, can include:
- Failed shift solenoid
- Blockages within internal ATF passages
- Internal mechanical failures
- Dirty or contaminated transmission fluid
- Failed PCM
- Failed transmission control module
- Low ATF level
What are the symptoms of a P0764 code?
Some P0764 codes may present no symptoms at all. Other symptoms can include:
- Harsh shifts
- Failure of the transmission to engage
- Failure to shift into a particular gear
- Stored code
- Lit MIL
- Poor fuel economy
- Limp-in mode
How does a mechanic diagnose a P0764 code?
Vehicles with OBD-II PCM systems use inputs on engine/turbine RPMs, transmission output speed and vehicle speed to calculate various engine drivability factors. This is essential for proper engine performance and fuel efficiency and engine/transmission longevity. The PCM initiates downshifts and upshifts and determines shift points by using shift solenoids.
Multiple shift solenoid codes are an indicator that a transmission slippage or delayed-engagement incident has occurred. The transmission is designed with a high pressure pump, driven by the torque converter, which circulates ATF through internal passages in the transmission housing and valve body. When transmission pressure is too low to enact gear changes, these codes may register.
A scanner/code reader and a digital volt/ohmmeter will be needed for a successful diagnosis.
Start off any transmission diagnostics by inspecting the transmission fluid on the dipstick. Top off fluid if low.
Fluid that appears dirty or smells burned should be considered as a potential cause. Burned fluid is a strong indication that the transmission was operated with a low level of ATF and may also mean catastrophic internal damage and failure.
If fluid smells or looks burned, drop the transmission pan to check for clutch materials or other debris in the pan. If such debris is found, a total rebuild of hard and soft parts, ATF flush/replacement and a new torque converter will likely be needed.
If no debris is present in the transmission pan, inspect the transmission’s internal wiring and connectors. Look out for shorted/burned wiring and replace as needed. Most applications will call for a complete replacement of the internal transmission wiring harness if problems are noted.
If all wiring/connectors/components are in good working order, connect the scanner/code reader to the diagnostic port. Record any stored trouble codes and freeze frame data. This information can be very helpful in tracking down intermittent conditions which may have resulted in a trouble code.
Clear diagnostic codes and test drive the vehicle to see if codes return. If not, the problem may be an intermittent condition which may need to be allowed to worsen and return in order to make a correct diagnosis.
Fill the transmission with ATF, and test drive to see if codes and symptoms return. If the transmission is shifting normally at normal operating temperature and the code doesn’t return, chances are the problem was due to low ATF level/pressure. If the code returns and transmission slips or shows delayed engagement, use a manual pressure gauge to check pump pressure.
Find a hydraulic pressure diagram for the vehicle and thread the end of the gauge to the proper port on the transmission housing. Record pump pressure and compare with manufacturer’s specs.
Low pump pressure can be due to clogged internal passages, a failed pump, failed electronic pressure regulator or failed solenoids. Pump replacement will mean transmission removal and partial disassembly.
If the transmission operates normally but the code immediately returns, check the affected shift solenoid for reference voltage and ground signals.
If reference voltage and ground circuits are open, check continuity and resistance in all circuits with the digital volt/ohmmeter. Be certain to disconnect any related control modules beforehand, to prevent controller damage.
Repair/replace any circuits and connectors as needed. Retest the system to see if repairs were successful. Use the factory wiring schematic and test the affected solenoid and all related circuits for continuity/resistance. Compare to factory specs.
Repair/replace any system circuitry/connectors/components that do not comply with factory specs. Retest the system.
If all system circuits are intact, use the scanner to attempt to manually activate the shift solenoid in question. If the shift solenoid is functioning properly and circuits are within manufacturer’s specs, suspect the PCM but remember that failed PCMs are rare.
If the shift solenoid will not activate manually, replace the solenoid and retest the system again.
Common mistakes while diagnosing P0746 code
More often than not, shift solenoid circuit malfunctions can trigger this code; instead of addressing circuit problems, the solenoids themselves are often misdiagnosed and replaced in error.
How serious is a P0764 code?
A P0764 code can result in a transmission that won’t shift, shifts harshly, won’t engage or goes into limp-in mode. A P0765 code should be addressed and repaired right away.
What repairs can fix a P0746 code?
Additional comments for consideration for P0764 code
Code setting parameters for a P0764 code can vary greatly from one manufacturer or even one manufacturer’s model to the next. Since misdiagnosis is easy and common with this code, it’s important to use a careful, process-of-elimination method to diagnose and repair a P0764 code.
Need help with a P0764 code?
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