Electronic Control Unit (ECU)

1. Diagnosis of fuel injection system is accomplished by removing connector from ECU and checking all electric circuits ending at connector. The tests will indicate condition of components and wiring leading to tested terminal or sensor.
2. If there is a problem after all tests are completed, and no malfunction was found, the ECU is most likely at fault. Replace ECU and recheck system to ensure that problem has been resolved.
3. Always check and repair all circuits before substituting a new control unit. If a new control unit is installed first, a faulty circuit may destroy new control unit in same manner as old one. There is no testing procedure for the ECU other than substitution.
4. To gain access to the ECU and harness connector, remove kick panel located in front of right front door. Disconnect wiring harness from ECU by pressing up on lock spring on top end of connector while pulling outward and down on top of connector. Do not pull connector straight out. See Fig 1 .
   Fig 1: Volvo ECU Harness Connector Removal

   Courtesy of VOLVO CARS OF NORTH AMERICA.
   NOTE: The connector terminals are now accessible, but should not be used for testing on their front side. Front of connector terminals can easily be damaged by test equipment.
5. To perform tests, cut boot clamp off of end of connector and slide cover off of connector. Always test from backside of connector. Terminal numbers are shown on both sides of connector.

Engine Speed Signal From Ignition Control Unit - Connect a voltmeter between fuel injection ECU terminal No. 1 and ground. Turn ignition on. Voltmeter should indicate battery voltage. Crank engine with starter. Voltmeter should indicate battery cranking voltage. If voltmeter does not indicate properly, check wiring harness.