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Home >> Volvo >> 1992 >> 940 GL, AW70 >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Self-Diagnostics - Fuel Injection >> Diagnostic Unit Led Does Not Flash
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Diagnostic Unit Led Does Not Flash

  1. If Red LED light will not flash when button is pressed or code will not flash, check grounds on intake manifold and for oxygen sensor. Check fuel pump relay and oxygen sensor heater fuses No. 4 and 6 (240), No. 1 and 11 (740) and No. 30 and 31 (940).
  2. If fuses are okay, go to next step. If any fuse is blown, check wiring for short. Remove glove box and right kick panel. Check ground wires at ECU. Ensure ignition is off. Remove fuel injection ECU fuses (in-line fuse near battery on 240, No. 1 on 740 and No. 31 on 940).
  3. Remove connector from ECU. Remove cover from connector. Check voltage for ECU memory by connecting voltmeter between terminal No. 4 and ground. Reading should be 12 volts. If 12 volts are not present, check wire between fuse and ECU connector.
  4. Turn ignition on. Connect diagnostic unit select cable to socket No. 2. Connect voltmeter between terminal No. 12 and ground. Reading should be 12 volts. If 12 volts are not present, check wire between diagnostic unit and ECU. Press button on diagnostic unit. Reading should be zero volts. If 12 volts are present, check diagnostic unit.
  5. Connect voltmeter between Blue wire in diagnostic unit connector and ground. Reading should be 12 volts. If 12 volts are not present, check circuit between ignition switch and diagnostic unit connector. Turn ignition off. Connect ohmmeter between Black wire in diagnostic unit connector and ground. Reading should be zero ohms.
  6. Connect ohmmeter between selector cable end and pin under function select button. Ohmmeter should indicate infinity. Press function select button, reading should be zero ohms. Connect a diode tester between LED on diagnostic unit and selector cable end.
  7. Connect Red lead of diode tester to pin under LED and Black lead to selector cable. If diode tester gives reading, LED is okay. If diode tester does not give reading, replace diagnostic unit. Turn ignition on. Connect voltmeter between terminal No. 35 on ECU connector and ground.
  8. Reading should be about 12 volts. Voltage should also be present in start position. Turn ignition off. Separately connect ohmmeter between ground and ECU terminals No. 5, 17, 19 and 29. Reading should be zero ohms.
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