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Ecu Power Circuits

WARNING: This page is about a different car, the 1990 Volvo 760 and 1990 Volvo 740. However, it is still accessible from the selected car via links, so may be relevant.
  1. Turn ignition on. Disconnect ECU connector. See Figure and Figure . Connect negative lead of DVOM to ground. Check for voltage at terminal No. 25 (while depressing brake pedal), and at terminals No. 27, No. 28 and No. 29 of ECU connector. All terminals should have battery voltage present except for terminal No 29 (.5-1.0 volt).
  2. If no voltage is present at following terminals, perform appropriate repair:
    • No. 25 - Check brake light switch. Replace if defective.
    • No. 27 - Replace defective solenoid relay.
    • No. 28 - Replace defective pump relay.
    • No. 29 - If voltage reading at terminal No. 27 is correct, voltage at terminal No. 29 should be .5-1.0 volt. If voltage at terminal No. 29 is not correct, replace solenoid relay.
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