DTC P0843: Transmission Fluid Pressure Sensor/Switch "A" Circuit High: Notes

WARNING: This page is about a different car, the 2021 Subaru Impreza. However, it is still accessible from the selected car via links, so may be relevant.

1. -

DTC detecting condition:

Immediately at fault recognition

Trouble symptom:

Shift characteristics malfunction

Wiring diagram:

CVT control system Ref. to WIRING SYSTEM (IMPREZA MODEL)>CVT CONTROL SYSTEM .

Courtesy of SUBARU OF AMERICA, INC.

CAUTION:

Use CHECK BOARD when measuring the TCM terminal voltage and resistance.
After servicing or replacing faulty parts, perform the last step of the basic diagnostic procedure. Ref. to TRANSMISSION (DIAGNOSTICS) (IMPREZA MODEL)>BASIC DIAGNOSTIC PROCEDURE .

CHECK INPUT SIGNAL FOR TCM .
1. Start the engine.
2. Warm up until the ATF temperature reaches to 40 - 70°C (104 - 158°F).
3. Depress the brake pedal, and shift the select lever to "D" range.
4. Shift the select lever to "P" range.
5. Stabilize the engine speed at idle.
6. Using the Subaru Select Monitor, read data of [Actual Secondary Pressure] in the [Data Monitor] of [Transmission]. Ref. to TRANSMISSION (DIAGNOSTICS) (IMPREZA MODEL)>DATA MONITOR .
Is [Actual Secondary Pressure] 0.5 - 1.5 MPa?

Yes: Check for poor contact of connector.

No: Go to 2.
CHECK HARNESS .
1. Turn the ignition switch to OFF.
2. Disconnect the TCM connector.
3. Disconnect the secondary pressure sensor connector.
4. Turn the ignition switch to ON.
5. Measure the voltage between TCM connector and chassis ground.
  Connector & terminal
  
  (T10) No. 5 (+) - Chassis ground (-):
  
  (T10) No. 33 (+) - Chassis ground (-):
Is the voltage approx. 0 V?

Yes: Go to 3.

No: Repair the short circuit of harness.
CHECK HARNESS .
1. Turn the ignition switch to OFF.
2. Measure the resistance between TCM connector terminals.
  Connector & terminal
  
  (T10) No. 5 - (T10) No. 33:
Is the resistance less than 1 Ω?

Yes: Repair the short circuit of harness.

No: Go to 4.
CHECK POWER SUPPLY FOR SECONDARY PRESSURE SENSOR .
1. Connect the TCM connector.
2. Turn the ignition switch to ON.
3. Measure the voltage between secondary pressure sensor connector terminals.
  Connector & terminal
  
  (AT6) No. 1 (+) - (AT6) No. 3 (-):
Is the voltage 4.5 V or more?

Yes: Replace the secondary pressure sensor. Ref. to CONTINUOUSLY VARIABLE TRANSMISSION (TR580 IMPREZA)>SECONDARY PRESSURE SENSOR . If the replacement of the sensor do not eliminate the malfunction, replace the TCM. Ref. to CONTINUOUSLY VARIABLE TRANSMISSION (TR580 IMPREZA)>TRANSMISSION CONTROL MODULE (TCM) .

No: Check for poor contact of connector, and if no fault is found, replace the TCM. Ref. to CONTINUOUSLY VARIABLE TRANSMISSION (TR580 IMPREZA)>TRANSMISSION CONTROL MODULE (TCM) .