Proper Tools and Testing Procedures

DIGITAL VOLT/OHM METER
Use a digital volt/Ohm meter (DVOM) with a minimum 10 mega-Ohms internal impedance when testing an Engine Control Module (ECM) or related components, unless use of an analog meter is specified by a testing procedure. Analog meters have low internal impedance and cause circuit "loading" in low voltage circuits, resulting in inaccurate measurements and possible damage to components. Use of a DVOM is necessary to obtain accurate measurements and avoid damaging low voltage ECM circuits and components.


TESTING PROCEDURES
Always follow recommended testing procedures. Never ground or apply voltage to a circuit unless specified by a testing procedure. ECM's provide a regulated constant low voltage source to some circuits, which may require a minimum resistance (impedance) to operate. Directly grounding or applying battery power to these circuits could damage the ECM and cause a system failure.