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Home >> Volvo >> 1986 >> 245 Base, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Fuel Injection System - BOSCH LH >> Testing >> Electronic Control Unit (Ecu)
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Electronic Control Unit (Ecu)

  1. Turn ignition off and disconnect connector from control unit. Remove panel beneath right side of dashboard, door step molding, protective moling and side panel. Lift catch upward and fold connector downward.
    CAUTION: Iginition must be off when disconnecting/connecting connector.
  2. Remove Plastic cover from connector.
    CAUTION: Do not insert instrument probe into front of connector. Experience has shown that this can case damage and introduce faults. Check terminals in holes through side of connector. Don't press too hard on terminals, only enough to make good electrical contact. Terminal number is stamped on side of connector.
  3. Check ground connections. Connect an ohmmeter between ground and terminals 5, 11, 19, 25 at the ECU. The resistance should be nearly 0 in all cases. Check that resistance is 0 even when the ohmmeter is connected between 11 and 19. Ground wires are connected to intake manifold.
  4. Check Lambda sond shielding wire. See Fig 1 . Check that the wire is connected to terminal 5. Check the ground connection between valve cover and firewall.
  5. Check that test point is not grounded. Connect ohmmeter between ground and terminal 12 (BL:W), 222. Connect ohmmeter between ground and terminal 22 (P), 149. Resistance should be infinite in both cases.
  6. Check the engine speed signal from the ignition system control unit. Connect a voltmeter between ground and terminal 1. Operate starter motor. Voltmeter should give the following readings:
    • Ignition Off equals 0 volts
    • Ignition On equals current from battery (ca 12V)
    • Starter motor in operation equals at least half current from battery.
  7. Check current supply. Turn ignition on. Connect a voltmeter between ground and terminal 18. Voltmeter should show battery voltage. Check for voltage when operating starter motor. Turn ignition off.
  8. Check fuel injection relay by connecting a voltmeter between ground and control unit terminal 9. Ground terminal 21. Relay should make circuit and meter should show battery voltage. The ground connection at 21 should remain in place.
  9. Check air mass meter circuit by moving the rubber cover on air mass meter to one side. Connect a voltmeter between air mass meter terminal 5 and 1. Voltmeter should show battery voltage. Ground terminal 17. Pump relay should activate fuel pumps and pumps should start operating. Connect a voltmeter between ground and terminal 87/2 in main relay. Meter should show battery voltage. Disconnect ground leads from terminal 17 and 21.
  10. Check Injector Circuits. Turn ignition off. Connect an ohmmeter between pump relay terminal 87/2 and ECU terminal 13. Correct resistance should be approximately 4 ohms. If meter shows approximately 5.3 ohms, either an injector or injector wire is defective. If meter reads approximately 8 ohms, 2 injectors or injector wires are defective. If meter shows 16 ohms, 3 injectors or injector wires are defective. Injectors may be tested separately. Each injector should have a resistance of 16 ohms.
  11. Check air contol valve. Connect an ohmmeter between terminal 87/2 on main relay connector and terminls 23 and 10 on control unit. Resistance should be approximately 20 ohms in both cases at 20°C (68°F).
  12. Check preheating resistor in Lambda sond. Connect ohmmeter between ground and terminal 87/2 on main relay connector. Resistance of cold Lambda sond (20°C = 68°F) = 3 ohms. Resistance of warm Lambda sond (above 350°C - 662°F) = 13 ohms. Reconnect the connector.
  13. Check air mass meter. Connect ohmmeter between terminals 6 & 7. Resistance should be approx. 3.7 ohms. Connect ohmmeter between 6 & 14. Resistance should be 0 and 1000 ohms depending on position of CO-screw.
  14. Check coolant temperature sensor. Connect ohmmeter between ground and terminal 2. Resistance is temperature-dependant. See TEMPERATURE RESISTANCE TABLE for coolant temperature sensor. If incorrect check resistance at sensor to see if fault is due to sensor or wiring. Check ground wire connected to intake manifold.
    TEMPERATURE RESISTANCE

    Applciation Ohms
    -10°C (14°F) 8260-10560
    20°C (68°F) 2280-2720
    80°C (176°F) 290-364
  15. Check throttle switch. Connect ohmmeter between ground and terminal 3. Resistance should be 0. Depress accelerator pedal slightly. Resistance should increase to infinity, switch opens. Connect a voltmeter between ground and terminal 12. Resistance should be infinity, switch open. Depress accelerator pedal slightly. Resistance should decrease to 0, switch closed. If incorrect measure resistance at switch to see if fault is due to switch or wiring. Check ground wire connected to intake manifold.
  16. Check assemble connector.
    CAUTION: Ignition must be off when disconnecting/connecting connector.

    Connect connector to control unit. Start the engine, if it does not start, then test with a new control unit.

  17. Check Lambda sound. Connect CO-meter. Connect meter to adapter next to the catalytic converter. Use 5151. See Fig 1
    WARNING: CO-meter adapter can be extremely hot.
    Fig 1: Meter To Adapter Connection
    G50F00294

    Warm up the engine. Disassemble the Lambda sond connector. Ground the wire that leads to the control unit. CO should increase to show that the wire and control unit are OK. Connect a voltmeter to Lambda sond. Meter should deflect ot show that the Lambda sond functions. If the CO is as specified, the voltage should be approximately 0.5-1.0 volt. Assemble the Lambda sond connector.

  18. Check air mass meter burn-off current.
    NOTE: Engine must be warm. Coolant temperature above 60°C (140°F).

    Connect a voltmeter between terminals 1 and 4. Increase engine speed to above 2100 rpm. Turn off engine. After 4 seconds meter pointer should deflect for 1 second. Disconnect voltmeter. Refit rubber cover. Disconnect CO-meter.

    WARNING: CO-meter adapter can be extremely hot.

    If no faults are found during fault tracing procedures and engine is still rough, then connect a new control unit and reinstall all panels, etc.

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