Power Steering Assist Disabled

Trouble symptom: 

• There is no assist due to power supply voltage failure.
• The STEERING warning light is normal but there is no power steering assist (steering feels heavy).

1. CHECK BATTERY. 

   Check the battery. Ref. to STARTING/CHARGING SYSTEMS(H4DOTC)>General Description . Ref. to STARTING/CHARGING SYSTEMS(H4DO)>Battery>INSPECTION .

   Is the check result OK?

   • Yes  : Go to 2. 
   • No  : Charge or replace the battery.
2. CHECK BATTERY TERMINALS AND FUSE. 

   Check the battery terminals and the fuse.

   Is the check result OK?

   • Yes  : Go to 3. 
   • No  : Repair or replace faulty parts.
3. CHECK DTC. 

   Using the Subaru Select Monitor, read all DTCs.

   Is DTC related to VDC system or ignition power supply system displayed?

   • Yes  : Perform the diagnosis according to DTC. Ref. to BRAKE CONTROL (DIAGNOSTICS)>List of Diagnostic Trouble Code (DTC) .
   • No  : Go to 4. 
4. CHECK DATA MONITOR. 
   1. Start the engine.
   2. Display the data monitor [Engine Speed] of the power steering control module using the Subaru Select Monitor.

   Is [Engine Speed] the same as that in the combination meter?

   • Yes  : Go to 5. 
   • No  : Check the CAN communication. Ref. to LAN SYSTEM (DIAGNOSTICS)>Basic Diagnostic Procedure .
5. CHECK DATA MONITOR. 

   Display the data monitor [EPS Status] of the power steering control module using the Subaru Select Monitor.

   Is [Assist limitation] displayed?

   • Yes  : It is possible that temporary assist limitation has occurred due to overheat protection. Stop the engine for approx. 10 minutes, and check.
   • No  : Go to 6. 
6. CHECK DATA MONITOR. 
   1. Using the Subaru Select Monitor, display the data monitor [Torque sensor main output][Torque sensor sub output] of the power steering control module.
   2. Move the steering wheel to the left and right.

   Do the values of [Torque sensor main output] and [Torque sensor sub output] change along with the operation?

   • Yes  : Go to 7. 
   • No  : Check the installation status of torque sensor, and check.
7. CHECK DATA MONITOR. 

   Display the data monitor [IG voltage] of the power steering control module using the Subaru Select Monitor.

   Is [IG voltage] stable? (While wiggling the harness)

   • Yes  : Go to 8. 
   • No  : Check the ignition switch and IG voltage harness, and repair the defective part.
8. CHECK CONNECTOR. 
   1. Turn the ignition switch to OFF.
   2. Disconnect the connector (B450).

   Are there any damages to terminal or other parts either on the power steering control module side or on the connector side?

   • Yes  : Repair the terminal.
   • No  : Replace the power steering control module. Ref. to POWER ASSISTED SYSTEM (POWER STEERING)>Power Steering Control Module .
   NOTE:

   • Power steering assist is not started unless both of the ignition switch ON signal and the engine speed signal are input.
   • In any of the following cases, the power steering assist is limited and steering wheel operation may become heavy.

     If the steering wheel is held to an end for a long time, or the steering wheel turning to right and left at slow speed is repeated during parking, the assist limitation (overheat protection control) may operate to prevent failures by overheat.

     In this case, by stopping the engine for approx. 10 minutes for cooling, the assist will start operating. While assist limitation (overheat protection control) is in active, Assist limitation is displayed in the EPS operating condition in the Subaru Select Monitor "Data monitor".

   • History can be confirmed on Overheating protection intervention history or IGN count from overheating protection (most recent) of "Data monitor".
   • The overheat protection control system is normal operation, therefore, the STEERING warning light will not come on and there will be no DTC displayed.
   • If the power steering system connector is disconnected while cooling under the overheat protection control, different DTC may be recorded. If there is no DTC and assist limitation is in active, stop the engine for approx. 10 minutes for cooling.