Matters needing attention in testing engine electronic control system with multimeter
(1) Unless otherwise specified during the test, pointer multimeters cannot be used to test computers and sensors, and high-impedance digital multimeters should be used. The internal resistance of the multimeter should not be lower than 1OKΩ.
(2) First check the condition of fuses, fusible links and terminals, and then check with a multimeter after troubleshooting these places.
(3) When measuring the voltage, the ignition switch should be turned on (ON), and the battery voltage should not be lower than 11V.
(4) When checking the waterproof connector with a multimeter, carefully remove the leather cover, and do not use too much force on the terminal when inserting the test pen into the connector for inspection. When testing, the test lead can be inserted from the rear end with wiring, or from the front end without wiring.
(5) When measuring resistance, gently shake the wire in the vertical and horizontal directions to improve accuracy.
(6) When checking the line open circuit fault, first disconnect the connector of the computer and the corresponding sensor, and then measure the resistance between the corresponding terminals of the connector to determine whether there is an open circuit or poor contact fault.
(7) When checking the ground short circuit fault of the line, the connectors at both ends of the line should be disassembled, and then the resistance value between the tested terminal of the connector and the body (ground) should be measured. Resistance value greater than 1MΩ is no fault.
(8) Before disassembling the electronic control system circuit of the engine, the power supply should be cut off first, that is, the ignition switch should be disconnected (OFF), and the wiring on the battery pole pile should be removed.
(9) The symbol of the grounding terminal on the connector varies with different models, and should be identified by referring to the maintenance manual.
(10) When measuring the voltage between two terminals or two lines, the two test leads of the multimeter (voltage file) should be in contact with the two terminals or two wires to be measured.
(11) When measuring the voltage of a certain terminal or a certain line, the positive test lead of the multimeter should be in contact with the terminal or line under test; and the negative test lead of the multimeter should be in contact with the ground wire.
(12) Checking the continuity of terminals, contacts or wires refers to checking whether the terminals, contacts or wires are energized and not disconnected, and can be checked by measuring the resistance value of the multimeter resistance file.
(13) When measuring resistance or voltage, it is generally necessary to disassemble the connector, so that the connector is divided into two parts, one part is called a sensor (or executive component) connector; the other part is called a sensor (or Actuating part) wire harness connector or a sensor (or actuating part) connector (or connector sleeve) on one side of the wire harness. For example, after removing the connector on the injector, one part is called the injector connector, and the other part is called the injector harness connector or the injector connector on the wire side. When measuring, it should be clear which part of the connector it is.
(14) All sensors, relays and other devices are connected to the computer, and the computer is connected to the executive components through wires, so when checking the fault, it can be tested on the corresponding terminal of the computer connector.
