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ECU Power Circuits

  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, 28 and 29 of ECU connector. All terminals should have battery voltage except for terminal No. 29, which should have .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. On 240, also check connectors under instrument panel, near glove box.
    • No. 27 - Replace defective solenoid valve relay.
    • No. 28 - Replace defective pump motor 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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