Standard Operation and Maintenance Procedures for Digital Multimeters
(1) Unless otherwise specified during testing, do not test the ECU or sensors with an analog multimeter. Use a high-impedance digital multimeter with an internal resistance of at least 10 MΩ.
(2) First inspect the condition of fuses, fusible links, and terminals. Resolve faults in these areas before testing with a multimeter.
(3) When measuring voltage, the ignition switch must be in the ON position, and battery voltage should be no less than 11 V.
(4) When checking waterproof connectors with a multimeter, carefully remove the rubber boot. Do not apply excessive force to terminals when inserting test probes. Testing can be done from the rear side with wiring or from the front side without wiring.
(5) When measuring resistance, gently wiggle the wiring vertically and horizontally to improve measurement accuracy.
(6) When diagnosing an open circuit, disconnect the connectors from the ECU and the corresponding sensor first, then measure resistance between the relevant terminals to determine whether an open circuit or poor connection exists.
(7) When checking for a short-to-ground fault, disconnect the connectors at both ends of the circuit, then measure resistance between the test terminal and the vehicle body (ground). A resistance value greater than 1 MΩ indicates no fault.
(8) Before disconnecting wiring in the engine electronic control system, disconnect power by turning the ignition switch to OFF and removing the battery cable.
(9) Symbols for ground terminals on connectors vary by vehicle model. Identify them carefully according to the service manual.
(10) When measuring voltage between two terminals or two circuits, place the multimeter (voltage range) probes in contact with the two terminals or two wires to be tested.
(11) When measuring voltage at a single terminal or circuit, connect the positive probe to the test terminal or circuit, and the negative probe to ground.
(12) Checking continuity of terminals, contacts, or wiring means verifying whether current can flow without interruption. This can be done by measuring resistance using the resistance range of the multimeter.
(13) When measuring resistance or voltage, connectors are usually disconnected and separated into two parts: one is the connector of the sensor (or actuator), and the other is the harness connector for that sensor (or actuator).For example, after disconnecting an injector connector, one part is the injector connector, and the other is the injector harness connector or harness-side injector connector.During measurement, clearly identify which connector section is being tested.
