Subaru Coupes/Sedans/Wagons 1985-1996 Repair Guide

Electronic Control Unit (ECU)

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OPERATION



The Electronic Control Unit (ECU) is required to maintain the exhaust emissions at acceptable levels. The module is a small, solid state computer which receives signals from many sources and sensors; it uses these data to make judgments about operating conditions and then control output signals to the fuel and emission systems to match the current requirements.

Engines coupled to electronically controlled transaxles employ a Vehicle Control Module (VCM) to oversee both engine and transaxle operation. The integrated functions of engine and transaxle control allow accurate gear selection and improved fuel economy.

In the event of an ECU failure, the system will default to a pre-programmed set of values. These are compromise values which allow the engine to operate, although at a reduced efficiency. This is variously known as the default, limp-in or back-up mode. Driveability is always affected when the ECU enters this mode.

REMOVAL & INSTALLATION



Except SVX
  1. Disconnect the negative battery cable.
  2.  
  3. If equipped with an air bag system, allow at least 10 minutes between the time the battery is disconnected and removing the ECU. This will allow time for the air bag module to power down.
  4.  
  5. Remove the lower trim panel retainer screws from below the steering column. Lift the panel off and place aside.
  6.  
  7. If equipped, remove the metal knee panel behind the trim panel, by removing the retainer screws.
  8.  
  9. Remove the retainer screws securing the ECU to the bracket next to or below the steering column.
  10.  
  11. Lower the ECU enough to access the control harnesses attached.
  12.  
  13. Disengage the harnesses from the ECU, by pushing in the lock tab and pulling the pug out of the ECU.
  14.  
  15. Remove the ECU.
  16.  

To install:
  1. Attach the harnesses to the ECU. Make sure the lock tab engages into place.
  2.  
  3. Position the ECU to the bracket, and secure in place with the retainer screws.
  4.  
  5. Install the metal knee panel, if equipped, using the retainer screws..
  6.  
  7. Install the trim panel and retainer screws.
  8.  
  9. Connect the negative battery cable.
  10.  

SVX

See Figure 1

Click image to see an enlarged view

Fig. Fig. 1: The ECU is located next to the driver's kick panel-SVX

  1. Disconnect the negative battery cable.
  2.  
  3. If equipped with an air bag system, allow at least 10 minutes between the time the battery is disconnected and removing the ECU. This will allow time for the air bag module to power down.
  4.  
  5. Remove the lower trim panel retainer screws from below the steering column. Lift the panel off and place aside.
  6.  
  7. Remove the metal knee panel behind the trim panel, by removing the retainer screws.
  8.  
  9. Remove the retainer screws securing the ECU to the bracket to the left of the steering column.
  10.  
  11. Lower the ECU enough to access the control harnesses attached.
  12.  
  13. Disengage the harnesses from the ECU, by pushing in the lock tab and pulling the pug out of the ECU.
  14.  
  15. Remove the ECU.
  16.  

To install:
  1. Attach the harnesses to the ECU. Make sure the lock tab engages into place.
  2.  
  3. Position the ECU to the bracket, and secure in place with the retainer screws.
  4.  
  5. Install the metal knee panel, if equipped, using the retainer screws.
  6.  
  7. Install the trim panel and retainer screws.
  8.  
  9. Connect the negative battery cable.
  10.  

 
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