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Test 7: ECM Communication Problem

  1. Perform sequence control. See SEQUENCE CONTROL  under SELF-DIAGNOSTICS. While performing sequence control, backprobe connector and measure voltage between ground and terminals No. 5, 12 and 14 at ABS/TCS control unit. Voltage should change from 2 volts or less to 4-5 volts. If voltage is as specified, replace ABS/TCS control unit. If voltage stays at 4-5 volts, replace ABS/TCS control unit. If voltage stays at 10-14 volts, go to next step. If voltage stays at 2 volts or less, go to step 4).
  2. Turn ignition off. Disconnect Engine Control Module (ECM) and ABS/TCS control unit connectors. Measure voltage between ground and terminals No. 5, 12 and 14 at ABS/TCS control unit 16-pin harness connector. See Figure . Voltage should be zero volts. Turn ignition on. Measure voltage between ground and terminals No. 5, 12 and 14. Voltage should be zero volts. If voltage is as specified, go to next step. If voltage is not as specified, repair wiring as necessary.
  3. Turn ignition off. Reconnect ABS/TCS control unit connectors. Backprobing connector, measure voltage between ground and terminals No. 5, 12 and 14 at ABS/TCS control unit 16-connector. See Figure . Voltage should be 2 volts or less. Turn ignition on. Backprobing connector, measure voltage between ground and terminals No. 5, 12 and 14. Voltage should be 2 volts or less. If voltage is as specified, replace Engine Control Module (ECM). If voltage is not as specified, replace ABS/TCS control unit.
  4. Turn ignition off. Reconnect ECM and ABS/TCS control unit connectors. Turn ignition on. Backprobing connector, measure voltage between ground and terminals No. 47, 73 and 74 at engine control module connector. See Fig 1 . If voltage is not 4-5.4 volts, go to next step. If voltage is 4-5.4 volts, go to step 6).
    Fig 1: Engine Control Module Harness Connector Terminals
    G96H20484Courtesy of SUBARU OF AMERICA, INC.
  5. Turn ignition off. Disconnect ECM and ABS/TCS control unit connectors. Measure resistance between ground and terminals No. 5, 12 and 14 at ABS/TCS control unit 16-pin harness connector. If all resistance readings are infinite, replace ECM. If any reading is not infinite, repair wiring harness as necessary.
  6. Turn ignition off. Disconnect Engine Control Module (ECM) and ABS/TCS control unit connectors. Measure resistance between terminals No. 5 at ABS/TCS control unit 16-pin connector and No. 73 at ECM connector. See Figure and Fig 1 . Measure resistance between terminals No. 12 at ABS/TCS control unit 16-pin connector and No. 74 at ECM connector. Measure resistance between terminals No. 14 at ABS/TCS control unit 16-pin connector and No. 47 at ECM connector. If all resistance readings are one ohm or less, replace ABS/TSC control unit. If any resistance reading is more than one ohm, replace wiring harness as necessary.
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