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Electronic Control Unit (Ecu) Test

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 proceeding to next step in test procedure. Always probe from rear of connector to avoid enlarging connector pin holes.
  1. Connect negative lead of voltmeter to a good ground near the ECU. Check for battery voltage at pin No. 18 of ECU harness connector with ignition on. See Fig 1 . Battery voltage should be present. If not, check fuse No. 22.
    Fig 1: 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 No. 18 and pins No. 5, 11 and 25 of ECU harness connector. Test light should light at all 3 pins.
  3. Connect test light between pin No. 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 No. 21 and check voltage at pin No. 9. Twelve volts should be present and relay should be heard to "pull down".
  4. Ground pins No. 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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