DTC P0890: TCM Power Relay Sense Circuit Low: Notes

WARNING: This page is about a different car, the 2022 Subaru WRX. 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:

Improper gear shifting

Wiring diagram:

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

DC power supply circuit Ref. to WIRING SYSTEM>POWER SUPPLY CIRCUIT>WIRING DIAGRAM

Engine electrical system Ref. to WIRING SYSTEM>ENGINE ELECTRICAL SYSTEM>WIRING DIAGRAM

Courtesy of SUBARU OF AMERICA, INC.

CAUTION:

Use CHECK BOARD when measuring the TCM.ECM 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

CHECK HARNESS .
1. Disconnect the TCM connector.
2. Remove the main relay.
3. Measure the resistance between TCM connector and M/B.
  Connector & terminal
  
  (B67) No. 8 - (M/B) No. 3:
  
  (B67) No. 24 - (M/B) No. 3:
  
  (B67) No. 40 - (M/B) No. 3:
Is the resistance less than 1 Ω?

Yes : Go to 2.

No : Repair the open circuit of harness.
CHECK HARNESS .
1. Disconnect the ECM connector.
2. Measure the resistance between ECM connector and M/B.
  Connector & terminal
  
  (B61) No. 29 - (M/B) No. 4:
Is the resistance less than 1 Ω?

Yes : Go to 3.

No : Repair the open circuit of harness.
CHECK HARNESS .
1. Remove the M/B fuse No. 21.
2. Measure the resistance between TCM connector and chassis ground.
  Connector & terminal
  
  (B67) No. 8 - Chassis ground:
  
  (B67) No. 24 - Chassis ground:
  
  (B67) No. 40 - Chassis ground:
Is the resistance 1 MΩ or more?

Yes : Go to 4.

No : Repair the short circuit of harness.
CHECK RELAY POWER SUPPLY .
1. Install the M/B fuse No. 21.
2. Measure the voltage between M/B and chassis ground.
  Connector & terminal
  
  (M/B) No. 1 (+) - Chassis ground (-):
  
  (M/B) No. 2 (+) - Chassis ground (-):
Is the voltage 10 V or more?

Yes : Go to 5.

No : Repair the open or short circuit of harness.
CHECK MAIN RELAY .
1. Turn the ignition switch to OFF.
2. Check the main relay. Ref. to FUEL INJECTION (FUEL SYSTEMS) (H4DOTC)>MAIN RELAY>INSPECTION
Is the check result OK?

Yes : Go to 6.

No : Replace the main relay.
CHECK INPUT SIGNAL FOR TCM .
1. Connect all connectors.
2. Install the main relay.
3. Using the Subaru Select Monitor, read data of [Control module voltage] in the [Data Monitor] of [Transmission]. Ref. to TRANSMISSION (DIAGNOSTICS)>DATA MONITOR
Is [Control module voltage] 10 V or more?

Yes : Current condition is normal. Check for poor contact in connectors or harnesses, and repair the defective part.

No : Go to 7.
CHECK MAIN RELAY .
1. Turn the ignition switch to OFF.
2. Replace the main relay.
3. Using the Subaru Select Monitor, perform the clear memory of [Transmission]. Ref. to COMMON (DIAGNOSTICS)>CLEAR MEMORY
4. Read the DTC of [Transmission] using the Subaru Select Monitor. Ref. to TRANSMISSION (DIAGNOSTICS)>DIAGNOSTIC TROUBLE CODE (DTC)
Is DTC P0890 displayed?

Yes : Replace the TCM. Ref. to CONTINUOUSLY VARIABLE TRANSMISSION (TR690)>TRANSMISSION CONTROL MODULE (TCM)

No : The original main relay is defective.