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Electronic Control Unit (Ecu)

NOTE: Ignition must be off when connecting or disconnecting the ECU. Remove wiring harness connector from ECU, prior to testing. Repair any problems as they are found, before proceding to next step in test procedure. Always probe from rear of connector to avoid elarging connector pin holes.
  1. Connect negative lead of voltmeter to a good ground near the ECU. Check for battery voltage at pin 18 of ECU harness connector when ignition is turned to "RUN" position. See Fig 1 . Battery voltage should be present. If no voltage is present, check fuse 22. Go to step 2).
    Fig 1: Saab ECU Harness Connector Pin Locations Locations are shown as viewed from rear of connector.
    G35434
  2. Check ECU ground locations by connecting a test light between pin 18 and pins 5, 11 and 25 of ECU harness connector. Test light should light at all three pins (5, 11 and 25).
  3. Connect test light between pin 1 of ECU harness connector and vehicle ground. Test light should pulse when engine is cranking. To check power output to ECU, ground ECU harness connector pin 21 and check voltage at pin 9. Twelve volts should be present and relay should be heard to "pull down".
  4. Ground pins 21 and 17 at ECU harness connector. Check voltage at Green/Red wire of 3-terminal limp-home test connector (connector is located near evaporator housing). Battery voltage should be present. If voltage is okay, pump and system relays are operating properly; proceed to TEMPERATURE SENSOR test. If voltage is not okay, go to SYSTEM RELAY TERMINALS test.
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