Check terminals visually

Fig 1: Checking Contact Resistance And Oxidation

Courtesy of VOLVO CARS OF NORTH AMERICA.

NOTE:

When checking the engine control module (ECM), do not remove the control module from the car before the main relay has interrupted the power supply. This may take up to 4 minutes after the ignition has been switched off and the engine cooling fan (FC) has stopped running.

Inspect the terminals visually when checking, or taking readings from, opened connectors.

Checks:

Check for oxidation. This can cause poor connections in the terminals
Check for damage to pins and terminals. Check that they are properly inserted into the connector. Check that the cable is properly connected to the pin or terminal. Check pins and terminals particularly carefully
Use a separate male terminal to check the female terminal. Check that they are secure: Pull on the pin.