A P1844 DTC for a Subaru indicates that there is an intermittent signal coming from the ‘A’ circuit in the transmission fluid pressure sensor. This vital transmission part is responsible for telling the ECU how much fluid pressure exists inside of the transmission. If there isn’t enough, then key systems will begin to shut down in order to avoid catastrophic failure.
How Serious is the Code?
Since your transmission operates on hydraulic pressure, not having enough will cause major damage to the internal components. To avoid this, and automatic transmission is fitted with a sensor that will trip if not enough pressure is present. If your vehicle has a P1844 diagnostic trouble code, then either the transmission fluid pressure sensor has failed. Or worse, there is an issue causing a reduction in transmission fluid pressure.
Symptoms of a P1844 include:
- Slow shifts
- Limp mode
- No vehicle movement
- Failed engine starts
- Dirty transmission fluid
- Clogged transmission filter
- Blocked hydraulic passage
- Failed transmission pump
- Failed pressure regulator system
- Failed transmission seals
- Failed transmission fluid pressure sensor
How to Diagnose the Code?
The first thing that should be done when diagnosing a P1844 OBDII diagnostic trouble code, is to check the condition that the level of the transmission fluid. If the transmission is clean and of the proper viscosity, then a pressure test should be performed on the transmission to determine if it is making enough hydraulic pressure. If it isn’t, then further tests will need to be performed to determine the source of the problem. If enough pressure is being made, then a new transmission fluid oil pressure switch will need to be installed.
What Repairs Will Fix P1844?
- Change transmission fluid/filter
- Flush transmission
- Replace transmission fluid pressure sensor
- Replace transmission seals
- Install remanufactured transmission