Repair and Diagnosis: Tools and Equipment

DIGITAL VOLT/OHM METER
Use a digital volt/ohm meter (DVOM) with a minimum 10 mega-ohms internal impedance when testing an ECU 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 ECU circuits and components.


TESTING PROCEDURES
Always follow recommended testing procedures. Never ground or apply voltage to a circuit unless specified by a testing procedure. ECU'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 ECU and cause a system failure.