P0844 code definition
The storage of a P0844 trouble code means that the Powertrain Control Module (PCM) has detected a deviation in the voltage signal received from the transmission fluid pressure sensor circuit. Some related codes include P0840, P0841, P0842, P0843, P0845, P0846, P0847, P0848, and P0849.
What the P0844 code means
The PCM uses data from the transmission fluid pressure sensor/switch to determine if the right amount of pressure is present for proper vehicle operation. When the pump pressure varies from what is needed, a P0844 trouble code is stored and the Check Engine light illuminates.
What causes the P0844 code?
A faulty electronic pressure control solenoid, blockage within the fluid passages of the transmission, a bad transmission fluid pressure sensor, a low fluid condition, dirty transmission fluid, a mechanical failure of the transmission, or even a faulty PCM or Transmission Control Module (TCM) are some common causes for the storage of a P0844 trouble code.
What are the symptoms of the P0844 code?
The symptoms of a P0844 trouble code range from no obvious signs to the inability to shift properly, and even a failure of the torque converter to work properly. Some other common symptoms of a P0844 trouble code include difficulty in shifting, transmission overheating, and a reduction in the vehicle's fuel efficiency. Also, when this code is stored, some PCMs can place the vehicle transmission into Limp-in mode.
How does a mechanic diagnose the P0844 code?
Mechanics need an advanced scanner, digital volt/ohmmeter, manual pressure gauge, a hydraulic pressure diagram, and a manufacturer's wiring diagram to properly diagnose a P0844 trouble code. In addition to this equipment, the mechanic should perform the following steps:
- Inspect the wiring, connectors, and components associated with the transmission, looking for any that have corrosion or damage.
- The mechanic should also check the transmission fluid, looking for a burnt smell or that looks abnormal in any way.
- If this is the case, the mechanic should pull the transmission pan and look for any signs of debris, such as from the clutch. This is an indicator that the transmission needs rebuilding and the torque converter replaced.
- Once fixed, the mechanic should fill the transmission fluid to a level to allow for repair of any leaks.
- After all leaks are fixed, the mechanic should fill the transmission fluid to an appropriate level. The mechanic should then clear the code, start the car, and allow it to reach a normal operating temperature.
- Test drive the vehicle to see if the transmission works smoothly and if the trouble code returns.
- If the trouble code returns, hook the scanner to the diagnostic connector and download any stored trouble codes, as well as the freeze frame data.
- Hook a manual pressure pump to the transmission to check the pressure of the hydraulic pump. The mechanic should use a hydraulic pressure diagram while doing so, comparing their findings with the manufacturer's specifications. The mechanic should also test the electronic pressure regulator at this time.
- Test the torque converter to see if it has gone bad.
- If the code returns after clearing it, the mechanic should use a digital volt/ohmmeter to check the reference voltage and ground signal of the transmission fluid pressure sensor, electronic pressure control solenoid, and all related circuits. If the voltage or ground are open, test the circuits for resistance and continuity. The mechanic should first disconnect all related control modules though to prevent controller damage.
- Clear the code to see if it returns. If it does, check the PCM to see if it has gone bad.
- Clear the codes once again, and re-test the system to see if the code persists.
Common mistakes when diagnosing the P0844 code
Often, mechanics erroneously replace a high pressure pump in response to this code when the problem actually lies with the transmission pressure sensor, electronic pressure control solenoid, or faulty wiring. This misdiagnosis of the problem usually results in the code returning.
How serious is the P0844 code?
The seriousness of a P0844 trouble code can range from not serious at all to an inoperable vehicle that fails to shift properly, if at all. A driver of a vehicle that has a stored P0844 trouble code should have the problem diagnosed and fixed as soon as possible to avoid any potential issues.
What repairs can fix the P0844 code?
To repair a P0844 trouble code, the mechanic should do the following:
- Replace any faulty or damaged wiring, connectors, or components.
- Rebuild the transmission if it was damaged due to a low fluid condition. The mechanic should also install a new torque converter when rebuilding the transmission.
- Repair any leaks detected in the transmission.
- Replace the hydraulic pump. The mechanic should keep in mind that this process requires the removal and partial disassembly of the transmission, so they should plan accordingly.
- Replace the torque converter if found to be faulty.
- Replace the transmission fluid pressure sensor, electronic pressure regulator, or electronic pressure control solenoid if faulty.
- Replace the PCM if bad. The mechanic should keep in mind that PCM failure is rare and the component should only be replaced after everything else has checked out. PCM replacement also requires the mechanic to reprogram it.
Need help with a P0844 code?
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This article originally appeared on YourMechanic.com as P0844 OBD-II Trouble Code: Transmission Fluid Pressure Sensor/Switch A Circuit Intermittent and was authored by Cheryl Knight.