The use of an analog (needle type) voltmeter is required if codes are to be read without a scan tool. Although the analog meter may be used for some component testing, the use of a high-impedance digital volt-ohmmeter is recommended for its accurate readout without affecting the circuit being tested.
The digital voltmeter or multimeter must be a high impedance unit, with 10 megohms of impedance in the voltmeter. This type of meter will not place an additional load on the circuit it is testing; this is extremely important in low voltage circuits. The multimeter must be of high quality in all respects. It should be handled carefully and protected from impact or damage. Replace the batteries frequently in the unit.
Other necessary tools include a quality tachometer with inductive (clip-on) pickup and a fuel pressure gauge with system adapters. A vacuum gauge may be required for certain test procedures.