Computers and Control Systems: Service Precautions

DVOM PRECAUTIONS
^ Never connect any tester (voltmeter, ohmmeter, etc.) to the Engine Control Module (ECM) when its connectors are disconnected. Attempting to do so may cause damage to the ECM.
^ Be sure to use a digital multimeter whose minimum resistance is more than one megohm per volt. Any other digital multimeter should not be used because accurate measurements are not obtained. (Use J 39200 or equivalent.)
^ When checking voltage at each terminal of the connector which is connected to ECM, be sure to connect negative (-) probe to body ground and, using a jumper wire connect the positive (+) probe to connector terminal being tested. Applying probes of digital multimeter improperly may cause a sensor or ECM to be shorted and damaged.