Check Key Switch Circuit

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.

Trouble symptom:

Engine does not start.

Trouble causes:

Key warning switch circuit malfunction
Key warning switch malfunction

Wiring diagram:

Immobilizer system Ref. to WIRING SYSTEM>IMMOBILIZER SYSTEM>WIRING DIAGRAM

Courtesy of SUBARU OF AMERICA, INC.

CAUTION:

When the body integrated unit (except for C0 model) or the immobilizer control module (C0 model) is replaced, registration of the immobilizer system is required. For details, refer to the "REGISTRATION MANUAL FOR IMMOBILIZER" provided as a separate volume.

CHECK POWER SUPPLY CIRCUIT .
1. Disconnect the connector from key warning switch.
2. Measure the voltage between key warning switch connector terminal and chassis ground.
  Connector & terminal
  
  (i181) No. 1 (+) - Chassis ground (-):
Is the voltage 10 V or more?

Yes : Go to 2.

No : Check the harness for an open or short between the key warning switch and fuse.
CHECK KEY WARNING SWITCH .
1. Insert the ignition key in the ignition switch. (OFF or ACC)
2. Measure the resistance between key warning switch connector terminals.
  Connector & terminal
  
  No. 1 - No. 2:
Is the resistance less than 1 Ω?

Yes : Go to 3.

No : Replace the key warning switch. Ref. to SECURITY AND LOCKS>KEY LOCK CYLINDERS
CHECK KEY WARNING SWITCH .
1. Remove the ignition key from ignition switch.
2. Measure the resistance between key warning switch connector terminals.
  Connector & terminal
  
  No. 1 - No. 2:
Is the resistance 1 MΩ or more?

Yes : Go to 4.

No : Replace the key warning switch. Ref. to SECURITY AND LOCKS>KEY LOCK CYLINDERS
CHECK DATA MONITOR .
1. Turn the ignition switch to ON.
2. Using the Subaru Select Monitor, check the following items under the [Data monitor] of [Body Control] or [Immobilizer]. Ref. to BODY CONTROL (DIAGNOSTICS)>DATA MONITOR Ref. to IMMOBILIZER (DIAGNOSTICS)>DATA MONITOR
  - Body Control (except for C0 model)
    - [key-lock warning SW Input]
  - Immobilizer (for C0 model)
    - key-lock warning SW Input
Is "ON" displayed?

Yes : Replace the body integrated unit (except for C0 and C5 models) or the immobilizer control module (C0 and C5 models). Ref. to BODY CONTROL/COMMUNICATION SYSTEM>BODY INTEGRATED UNIT Ref. to SECURITY AND LOCKS>IMMOBILIZER CONTROL MODULE

No : Go to 5.
CHECK HARNESS BETWEEN KEY WARNING SWITCH AND BODY INTEGRATED UNIT (EXCEPT FOR C0 MODEL) OR IMMOBILIZER CONTROL MODULE (C0 MODEL) .
1. Turn the ignition switch to OFF.
2. Disconnect the connector from the body integrated unit (except for C0 model) or the immobilizer control module (C0 model).
3. Measure the resistance between key warning switch connector terminal and body integrated unit (except for C0 model) or immobilizer control module (C0 model) connector terminal.
  Connector & terminal
  
  Body integrated unit (except for C0 model)
  
  (i181) No. 2 - (i82) No. 19:
  
  Immobilizer control module (C0 model)
  
  (i181) No. 2 - (i94) No. 3:
Is the resistance less than 10 Ω?

Yes : Replace the body integrated unit (except for C0 model) or the immobilizer control module (C0 model). Ref. to BODY CONTROL/COMMUNICATION SYSTEM>BODY INTEGRATED UNIT Ref. to SECURITY AND LOCKS>IMMOBILIZER CONTROL MODULE

No : Repair harness between key warning switch and body integrated unit (except for C0 model) or immobilizer control module (C0 model).