Automotive engine wire harness inspection and replacement methods Oct 23, 2023

Automobile wire harness fault type

1. Natural damage

The use of wire harness exceeds the use period, making the wire aging, the insulation layer is broken, the mechanical strength is significantly reduced, causing short circuit between the wires, open circuit, taking the iron, etc., resulting in the wiring harness burning out. Wiring harness terminal oxidation, deformation, resulting in poor contact, etc., will cause electrical equipment can not work normally.


2. The cable harness is damaged due to an electrical fault

When the electrical equipment overload, short circuit, iron and other faults, may cause wiring harness damage.


3. Human fault

When assembling or repairing auto parts, metal objects will crush the wiring harness, causing the insulation layer of the wiring harness to break; The auto wiring harness is improperly positioned; The lead position of the electrical equipment is connected incorrectly; The positive and negative battery leads are reversed. When inspecting a circuit fault, random connection, random cutting of the wiring harness wire, etc., can cause the electrical equipment to work abnormally, and even burn the wiring harness.


Inspection method of automobile wire harness


1. Visual inspection method

When a certain part of the automobile electrical system fails, there will be smoke, sparks, abnormal noise, burnt odor, high temperature and other abnormal phenomena. By listening, touching, smelling and seeing the sensory organs of the human body, the car wiring harness and electrical appliances are visually inspected, and then the fault is determined, which greatly improves the maintenance speed. For example, when the car line fails, there will often be smoke, sparks, abnormal noise, burnt odor, high temperature and other abnormal phenomena. Through visual inspection, the location and nature of the fault can be quickly determined.


2. Instrument inspection method

The method of diagnosing the fault of automobile circuit by using the comprehensive fault diagnosis instrument, multimeter, oscilloscope, current clamp and so on. For electronic control system vehicles, the fault diagnosis instrument is generally used to find the fault code to confirm the fault range. Then use a multimeter, current clamp or oscilloscope to check the voltage, resistance, current, or waveform of the relevant circuit, and diagnose the fault point of the wire harness lead.


3. Tool inspection method

The test light inspection method is more suitable for checking the short circuit fault of the conductor. The use of temporary test light method should pay attention to the power of the test light should not be too large, especially when testing whether the control output terminal of the electronic controller has an output and whether there is enough output, to prevent the use of controller overload damage. It is best to use diode test lights.


4. Check method for wire crossover

The crossover method means that a wire will be suspected of having a fault after short-connecting the line, observe the change of the instrument pointer or the working condition of the electrical equipment, so as to determine whether there is a break or poor contact fault in the circuit. Crossover refers to the operation of connecting two points in a circuit with a wire, and the potential difference between the two points of the circuit is zero, not a short circuit.


Repair of wiring harness


Minor mechanical damage, insulation damage, short circuit, loose wiring, corrosion of wire joints or poor contact can be repaired. Cable harness fault repair, must completely eliminate the root cause of the failure, to prevent the failure to occur again may often be due to the vibration friction of the wire and metal parts caused by the root cause.


Replacement of wiring harness

For wiring harness aging, serious damage, internal wire short circuit or internal wire short circuit failure, usually need to replace the wiring harness.


1. Check the cable harness quality before replacing the cable harness.


In order to ensure that the harness is safe and reliable, it must be strictly controlled before use, should be certified and inspected, and should not be used when defects are found to prevent the harm caused by unqualified products. Conditions, it is best to use instruments to check.


Check whether the wiring harness is damaged, whether the connector is deformed, whether the terminal is corroded, whether the connector itself, the wiring harness and the connector are in poor contact, and whether the wiring harness is short-circuited or short-circuited. The inspection of the wire harness is essential.


2. Remove the fault of all the electrical equipment on the car before replacing the wiring harness.


3. Replace the cable harness.


(1) Prepare the tool for removing and assembling the wiring harness.

(2) Remove the battery of the faulty vehicle.

(3) Disconnect the connector of the electrical equipment connected to the wire harness.

(4) Keep good work records throughout the process.

(5) Loosen the wiring harness fixing.

(6) Remove the old wiring harness and assemble the new wiring harness.


4. Verify the correctness of the new wiring harness connection.


Whether the wiring harness connector is correctly connected to the electrical equipment is the first thing to confirm, but also to ensure that the positive and negative connections of the battery are correct.


When checking, you can show the cable that is not connected to the battery, and use the lamp (12V, 20W) to do the test light. Before this, the other electrical equipment on the car should be turned off, and then the test light string is connected between the negative battery and the frame. As soon as there is a problem with the circuit, the test light starts to brighten.


When the circuit is troubleshooting, take off the light bulb and connect it with a 30A capacity fuse between the negative battery terminal and the frame. At this time, the engine should not start, the corresponding power equipment on the car should be connected one by one, and the relevant lines should be comprehensively inspected one by one.


5. Power working inspection.


If the electrical equipment and related lines are confirmed that there is no problem, you can take off the fuse, connect the battery to the wire, and carry out power inspection.


6. Check the installation of the cable harness.


Preferably, the wiring harness installation should be checked to ensure that the wiring harness is installed correctly and securely.





Although the hidden hidden trouble of automobile wiring harness is strong, as long as the practical work of automobile maintenance is combined with careful research and application of modern technical means and methods, the fault diagnosis still has rules to follow; Similarly, in the work of wire harness repair and replacement, research should be strengthened, and maintenance norms should be constantly improved to ensure the safety and reliability of vehicle use and maintenance.

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