DTC P0842: Transmission Fluid Pressure Sensor/Switch "A" Circuit Low: Notes

DTC detecting condition:

Immediately at fault recognition

Trouble symptom:

Shift characteristics malfunction

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)>BASIC DIAGNOSTIC PROCEDURE .

Wiring diagram:

CVT control system Ref. to WIRING SYSTEM>CVT CONTROL SYSTEM .

Courtesy of SUBARU OF AMERICA, INC.

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. Read the data of [Actual line press.] using Subaru Select Monitor. Ref. to TRANSMISSION (DIAGNOSTICS)>DATA MONITOR .
Is [Actual line press.] 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 transmission connector.
4. Measure the resistance between TCM connector and transmission connectors.
  Connector & terminal
  
  (B54) No. 3 - (E42) No. 15:
  
  (B54) No. 4 - (E42) No. 18:
  
  (B54) No. 17 - (E42) No. 3:
Is the resistance less than 1 Ω?

Yes: Go to 3.

No: Repair the open circuit of harness.
CHECK HARNESS .
Measure the resistance between TCM connector and chassis ground.

Connector & terminal

(B54) No. 4 - Chassis ground:

(B54) No. 17 - Chassis ground:

Is the resistance 1 MΩ or more?

Yes: Go to 4.

No: Repair the short circuit of harness.
CHECK TRANSMISSION HARNESS .
CAUTION: Start work after ATF cools down.
1. Remove the transmission oil pan.
2. Disconnect the line pressure sensor connector.
3. Measure the resistance between transmission connector and line pressure sensor connector.
  Connector & terminal
  
  (T19) No. 3 - (AT2) No. 1:
  
  (T19) No. 15 - (AT2) No. 3:
  
  (T19) No. 18 - (AT2) No. 2:
Is the resistance less than 1 Ω?

Yes: Go to 5.

No: Replace the transmission harness. Ref. to CONTINUOUSLY VARIABLE TRANSMISSION (TR690)>TRANSMISSION HARNESS .
CHECK TRANSMISSION HARNESS .
Measure the resistance between transmission connector and chassis ground.

Connector & terminal

(T19) No. 3 - Chassis ground:

(T19) No. 18 - Chassis ground:

Is the resistance 1 MΩ or more?

Yes: Go to 6.

No: Replace the transmission harness. Ref. to CONTINUOUSLY VARIABLE TRANSMISSION (TR690)>TRANSMISSION HARNESS .
CHECK LINE PRESSURE SENSOR POWER SUPPLY .
1. Connect the TCM connector.
2. Connect the transmission connector.
3. Turn the ignition switch to ON.
4. Measure the voltage between line pressure sensor connector terminals.
  Connector & terminal
  
  (AT2) No. 1 (+) - (AT2) No. 3 (-):
Is the voltage 4.5 V or more?

Yes: Replace the control valve body. Ref. to CONTINUOUSLY VARIABLE TRANSMISSION (TR690)>CONTROL VALVE BODY .

No: Check for poor contact of connector, and if no fault is found, replace the TCM. Ref. to CONTINUOUSLY VARIABLE TRANSMISSION (TR690)>TRANSMISSION CONTROL MODULE (TCM) .