Auto Relay Overview

Auto Relay Overview

Relay is a kind of automatic control device when the input quantity (electricity, magnetism, sound, light, heat) reaches a certain value, the output quantity will change in a jump. 

Automobile relays are relays used in automobiles. These relays have high switching power and high impact resistance and vibration resistance. The power supply in the car is now 12V, and the coil voltage is mostly designed to be 12V. 

Due to the battery power supply and unstable voltage; the harsh environmental conditions, the suction voltage V≤60%VH (rated operating voltage); the coil overvoltage is allowed to reach 1.5VH. 

The power consumption of the coil is relatively large, generally 1.6 to 2W, and the temperature rise is relatively high. The environmental requirements are quite demanding: in the engine compartment, the ambient temperature range is -40°C to 125°C, and the ambient temperature range for other locations is -40°C to 85°C; the relays used in the engine compartment must be able to withstand sand, dust, water, and salt, The infringement of oil; vibration and shock are quite harsh.

Auto Relay Classification

According to the difference of main functions, auto relays can be divided into the following types.

   ① Electrical switch type relay. For example, the fuel pump relay of Santana 2000GSi car AJR engine, which is installed in the central power distribution box, is used to control the power supply of electric fuel pump, air flow sensor, canister solenoid valve and oxygen sensor heater.

  ② Direction control type relay. For example, the relay of the electric seat system is used to control the current direction of the two-way motor. When the corresponding switch is manipulated for commutation, the relay causes the motor to rotate in different directions, so that the electric seat moves in different directions purpose.

   ③ Integrated relay. For example, the integrated relay in the headlight system of the Lexus LS400 car. Its function is to perform automatic extinguishment of the headlights, fog lights and rear fog lights, and cut off the path to the light control according to the signals from the GAUGE fuse and door control light switch. Switch current.

Another example is the start lock and reversing light relay (J226) of 01M automatic transmission (adopted by Volkswagen cars). It is composed of 2 relays and is installed on an additional relay bracket under the combination instrument. The number on the above is “175”, which is specifically installed at the 15th position of the relay box. When the shift lever is in the forward gear, J226 can control the starter circuit to not be energized to prevent the driver from misoperation; when the shift lever is in the R position, J226 turns on the reversing light. When J226 fails, the transmission will not enter the emergency state, and the A/T ECU will not record the failure code.

Auto Relay Selection Guide

  Automatic relays can be analyzed and studied item by item according to the following points: appearance and installation method; input parameters; output parameters; environmental conditions; electromagnetic compatibility; installation and use requirements.

   1. Shape, installation method, installation size

   Automotive relays must be selected according to the specific requirements of the vehicle, shape, installation method, and installation feet. The following principles are generally adopted:

   1. Products that meet the same load requirements have different dimensions. Depending on the allowed installation space, products with low height or small installation area can be selected.

   2. The installation methods of automotive relays are PCB board type, ISO socket installation type, ISO 280 socket installation type and shell fixing and card installation methods. For the relays with small size and infrequent replacement, the PCB board type is generally selected, and for the relays that are frequently replaced, the socket installation method is selected. For relays whose main loop current exceeds 20A, the socket quick connection type is generally selected to prevent large currents from passing through the circuit board and causing heat damage to the circuit board (except short-term working relays). For bulky relays, the shell-mounted type can be selected to prevent damage to the mounting feet under impact and vibration conditions.

   Second, input parameter selection principle

   The input parameters of automobile relay are: 12VDC input parameter, 24VDC input parameter, 12VDC pulse input parameter, 24VDC pulse input parameter. Consider the following parameters when selecting: Coil rated voltage Coil power consumption Operating voltage, release voltage Maximum continuous energizing current Coil Resistance Coil temperature rise Pulse width of pulse input parameters (magnetic holding relay).

   Input parameter selection concern:

  1. Ambient temperature: the impact of the ambient temperature and the coil temperature rise on the operating voltage is generally divided into the engine compartment (maximum temperature requirement is 125℃) and the cockpit (maximum temperature requirement is 85℃); the relay coil resistance varies with temperature Changes vary, and this has obvious effects on the relay operation and release voltage. Each time the temperature rises by 1℃, the coil resistance will increase by 4‰. When the relay coil is energized for a period of time, the coil heats up. At this time, the relay contact switching operation is performed, and the operating voltage is higher than the cold operating voltage.

   2. Operating voltage: When driving relays with transistors and integrated circuits, pay attention to the voltage drop of transistors and integrated circuits and the destructive effect of the relay coil back-EMF on transistors and integrated circuits.

  1. Rated voltage of the coil: After the normally open contact of the relay is closed, it is generally required that a voltage above the minimum operating voltage should be applied to the coil. It is not recommended to use a low holding voltage for automotive relays, because it will weaken the product’s vibration resistance when the vehicle is violently bumpy Misoperation may occur.
  2. The maximum working voltage of the coil: In order to meet the requirements of low operating voltage (60% rated voltage), automotive relays are generally designed to consume high power. The voltage value applied to the coil for a long time should generally be less than 120% of the rated voltage. For 130% rated voltage and above, you need to contact the relay manufacturer for technical support. Especially when it is used under high temperature, it will cause the coil temperature to be too high, and the aging will be accelerated-eventually the coil insulation will be damaged and the inter-turn short circuit will fail.

   5. Release voltage: The release voltage of the car relay is generally 10% of the rated voltage. When the residual voltage on the line is too large, the relay will not be released.

   3. Output parameters

The following parameters should be considered when selecting the relay output parameters: Number of contact groups Contact Form Contact Load Contact Material Electrical life, mechanical life 1, Load type Most domestic relay load capacity, only the maximum pure resistive load is marked, which gives the user There are two kinds of misunderstandings when selecting the relay load, which leads to mistakes in model selection. One of the misunderstandings is that users often use not purely resistive loads, but inductive, lamp, motor or capacitive loads. The load size is equal to or close to resistive loads; the second misunderstanding is that the load can It can adapt to the rated load. It should be noted that a relay that can reliably convert a 10A resistive load is not necessarily a 10A inductive load, and it may not necessarily be able to reliably convert a 10mA load. Because the failure mechanism of electrical contact under different load conditions is completely different. The power supply of the automobile system uses DC, and the DC voltage has no zero-crossing point, and the arc is generated at the moment of contact opening, and due to the continuous application of the applied voltage, only the arc is elongated and cannot be extinguished. The thermal energy of the arc will severely burn the contacts, and the DC current will always flow in one direction, which will aggravate the contact material transfer. The load capacity of most automotive relays is only nominally a resistive load, but the actual use of automotive relays is often not resistive loads, but inductive loads, lamp loads, and motor loads. Due to the high inrush current, the steady-state load of the contacts The size should be derated according to the size of the inrush current. It should be emphasized that contact failure is the main cause of relay failure. The electrical contact characteristics, failure phenomena and failure mechanism of the contacts in different load types and different load size conditions are different.

   2. Contact material The contact material is the most critical material used in the relay, and its performance determines the quality level of the relay.

   Fourth, the principle of time parameter selection

When selecting the time parameters of the relay, the following parameters should be considered: Pick-up time Release Time Pick-up rebound time Release rebound time The relay time parameters are defined as follows:

  Typical waveform diagram on the oscilloscope during time test ①Normally open contact ②Normally closed contact ③ Break-before-make contact O b s Cautions when selecting: Operating time Rebound Time Bridge time

  ④ Break-before-make contact r t c Release time Conversion time reaches stable closing time

   1) When using automotive relays, the time parameters are generally not concerned.

   2) Pay attention to the time when the car relay is combined, such as the flash frequency.

   V. Principles for selection of environmental conditions

  The following environmental parameters should be considered when selecting relays:

   1. Temperature

   1) Under high temperature conditions, the insulation material softens and melts; under low temperature conditions, the material cracks and the insulation resistance of the insulation decreases, resulting in failure. However, engineering plastics with excellent performance can meet the requirements.

   2) The alternating action of high and low temperatures causes the structure to loosen and the position of the moving parts to change, resulting in loss of control of suction and release, and poor or non-contact contact.

   3) At low temperatures, the moisture inside the relay condenses and freezes, resulting in reduced insulation performance.

   4) Under high temperature conditions, the coil resistance increases, and the suction voltage increases accordingly, resulting in non-suction or non-suction, causing the relay to fail.

   5) Under high temperature conditions, when the contact switches the power load, the arc interruption ability is reduced, the contact corrosion and metal transfer are increased, the possibility of failure is increased, and the life is shortened.

   2. Damp heat

  Damp heat poses a threat to the performance of the relay, the specific performance is as follows:

   1) Long-term humid heat will directly lead to a decrease in insulation resistance level, resulting in complete failure. Especially when the relay insulation is contaminated by sand and dust during long-term bare storage or use, then the heat and humidity will cause the insulation to fail.

2) Under the condition of humid heat, the coil is disconnected due to electrochemical corrosion or mildew, and the electrochemical corrosion and oxidation of the contacts are intensified; the corrosion rate of metal parts increases significantly, the performance of the relay deteriorates, and the working reliability deteriorates, so that Completely invalid.

   3) Under hot and humid conditions, when the contact is switched on while the load is live, the arcing phenomenon is intensified, resulting in shortened electrical life. For electronic products used in tropical and subtropical regions, the heat and humidity issues must be fully considered in product design and material selection.

   3. Sand and dust

   Sand and dust pollution lead to the failure of the relay, which has not attracted enough attention from users. Under natural environmental conditions or general industrial workshop environmental conditions, especially the electronic devices used in automobiles, sand and dust often penetrate into the relay through the heat dissipation holes and cracks. After a long period of time, after starting the machine, you can find the accumulation of dust, resulting in activity The components are not rotating (sliding) and are stuck; the electrical contact of the contacts fails; under the action of moisture, the corrosion of the metal parts increases, and the insulation performance of the insulating parts decreases, resulting in failure. Some relays for power protection and automotive relays have passed the inspection before leaving the factory. After one or two years of operation, the relays continue to malfunction. The hazards of sand and dust pollution must be fully considered when designing and using. Users put forward specific requirements according to practical needs.

   4. Chemical atmosphere pollution

Organic vapors, oxygen, sulfur dioxide, salt mist, etc. in the ambient atmosphere have an erosive effect on the relay contacts, metal parts, coils, and insulating parts, resulting in poor electrical contact of the contacts, resulting in failure; lead to rusty wire breakage and insulation The level drops. Chemically harmful gases are common in nature, but on different occasions, the types of harmful gases (steam) are different. The adoption of technological measures can reduce and eliminate their erosion, but the cost will increase significantly. Such as military sealed relays, through long-term high-temperature vacuum baking, filled with high-purity N2 in the relay cavity, using electron beam (or laser) for sealing welding, the leakage rate can reach 10-8pa.cm3/s; contact plating 1~3u gold. Civil relays are limited by price, and generally only plastic enclosures are used to mitigate the erosion of harmful gases (vapors) in the atmosphere. When using, according to the size of the relay load and the quality of the environment, the process holes can be opened as appropriate to improve heat dissipation capacity and reduce internal Organic vapor and sulfur dioxide pollute the contact surface.

   5. Mechanical vibration

   Relays will encounter vibrations in a certain frequency range and acceleration values ​​around strong power equipment and during transportation; random vibrations can represent the on-site vibration stress generated by missiles, high-thrust jets and rocket engines. The impact of vibration on the relay is shown in:

  A. Vibration may cause mechanical structural parts to loosen, fatigue and break;

  B. The closed contact is invalid due to the instantaneous opening of vibration greater than the time specified in the standard;

  C. The open contact is invalid due to the instantaneous closure of vibration for more than the time specified in the standard;

  D. Relative movement between moving parts, resulting in noise, wear and other physical failures.

   6. Shock

   Relays are often subjected to mechanical shock during transportation, handling, and use. The impact of shock on the relay is shown in:

   1) Due to the impact, the structure becomes loose, damaged, broken and loses its working ability.

   2) Due to the impact, the closed contact generates an instantaneous opening greater than the specified requirements and fails; the open contact generates an instantaneous closure greater than the specified requirements and fails. Therefore, with regard to (1), the relay is required to have impact resistance performance, and the measurement results of the specified items performed before and after the test should meet the product standard requirements. For (2), the relay should have anti-shock stability, and the contact state of the contacts should be dynamically monitored.

   V. Safety parameter selection principles

  Relay safety requirements consider the following parameters:

   1. Insulating material The insulating material used in the product should have good temperature resistance, and the long-term working temperature should reach 125℃.

   2. Insulation withstand voltage level The withstand voltage of the relay is divided into the withstand voltage between the contacts and insulation resistance; the withstand voltage between the contact coils and insulation resistance. Typical values ​​for automotive relays are 500 VAC withstand voltage and 100 MΩ insulation resistance.

   3. Electromagnetic compatibility Electromagnetic compatibility (EMC) is the ability of automotive relays to work without or without interference when working in an electromagnetic environment. EMC has become an important criterion for product quality. Electromagnetic compatibility (EMC) is divided into electromagnetic interference (EMI) and electromagnetic anti-interference (EMS). Since the automotive relay uses a unified power supply, high voltage will be formed when the relay coil is disconnected, which interferes with other systems and modules. Therefore, plug-in automotive relays usually have parallel resistance or diodes for transient suppression, making the coil back EMF less than 100V. When the relay contact is opened, an arc is generated and electromagnetic waves are emitted, which will affect the IC’s operation. If this happens, an arc extinguishing circuit can be added to the contact. The distance between the relay and the IC can also be increased appropriately.

Working Principle of Auto Relay

When a certain voltage or current is applied to both ends of the electromagnetic relay coil, the magnetic flux generated by the coil passes through the magnetic circuit composed of the iron core, the yoke, the armature, and the working air gap of the magnetic circuit. Under the action of the magnetic field, the armature attracts the pole surface As a result, the normally closed contact of the contact is opened, and the normally open contact is closed; when the voltage or current at both ends of the coil is less than a certain value, and the mechanical reaction force is greater than the electromagnetic attraction force, the armature returns to the initial state, and the normally open contact is opened. The normally closed contact is closed.

Then, the car relay can be regarded as an assembly composed of two parts: a control circuit for coil operation and a main circuit for contact operation. In the control circuit of the relay, there is only a small working current. This is because the contact capacity of the operating switch is small, and it cannot be used to directly control the load with large power consumption. It can only be controlled through the contact of the relay. On and off.

Relay is not only a control switch, but also a control object (actuator). Taking the fuel pump relay as an example, it is the control switch of the fuel pump, but the coil of the fuel pump relay can only form a loop through the ground point of the electronic control unit when the transistor in the electronic control unit is turned on.

Auto Relay Storage and Transportation Environment

Avoid direct sunlight and maintain normal temperature, normal humidity and normal pressure; Temperature: 10℃~35℃ Humidity: 5~85%RH Pressure: 86~106kPa

In a high temperature and high humidity environment, when the ambient temperature changes abruptly, condensation may form inside the relay. Especially when shipping by sea, it is especially easy to produce condensation. Please pay attention to the transportation environment. Condensation is the phenomenon that water vapor condenses into water droplets when the temperature changes from high temperature to low temperature or from low temperature to high temperature and high humidity in high-temperature and high-humidity environments. Condensation will cause a decrease in insulation, wire breakage, corrosion, etc.

Low-temperature icing: The phenomenon of moisture freezing when the temperature drops below the freezing point in the state where moisture is attached to the relay in dew and high-humidity environments. Icing may cause adhesion of moving parts, delay in action or ice cubes between the contacts, causing the contacts to malfunction.

Plastics may become brittle in low temperature and low humidity environments.

Long-term storage in high-temperature, high-humidity, organic gas, and sulfide gas environments will produce sulfide and oxide films on the contact surface, resulting in unstable contact and contact failure. Please pay attention to the packaging form to minimize the influence of humidity, organic gas, sulfide gas, etc.

The relay should be stored and installed in a clean environment. Please use a dust cover or plastic relay in the presence of dust pollution.

Should pay attention to monitor the storage temperature, try to avoid the relay storage time is too long.

2. Storage and transportation stress During transportation, if a large drop impact is applied to the relay, it may cause a malfunction. Please pay attention to whether the appearance of the packaging material is complete. The relay is packed in a long tube. When the number of relays is small, if there is no limit, it will slip and affect the appearance and characteristics of the relay. Pay special attention.

Auto relay installation method

1. Mounting direction If the mounting direction is the same as the direction of the shock resistance of the relay, the performance of the relay can be fully utilized. It is recommended to make the impact direction perpendicular to the movement direction of the contact and armature, which can effectively improve the vibration resistance and shock resistance of the normally closed contact in the non-excited state. During installation, the contact axis of the relay is parallel to the ground to avoid contact spatter and char on the contact surface and improve contact reliability. Multiple sets of relays should avoid the small load contacts below the large load contacts.

2. Installation at close range When multiple relays are installed at close range, it will cause abnormal heat generation, generally 2mm pitch is recommended. Installing a polar or magnetic holding relay at close range will affect the operating voltage.

3. The relay is installed on the case. The case cannot be removed and installed first. To prevent loosening, damage, and deformation, please use a spring washer. The tightening torque should be within the range of 0.5~70N·m.

4. The insertion strength of the plug-in relay is recommended to be 40-70N.

Precautions for the use of auto relays

  1. Precautions for coil input

   1. The rated voltage is the guarantee of the working reliability of the relay. Although the relay can work when the coil voltage exceeds the operating voltage, it will malfunction under strong shock. If the coil voltage exceeds the maximum operating voltage, it will cause the coil insulation to fall, turn-to-turn short circuit, and burnout.

   2. The coil resistance value of the relay will change by about 0.4% ℃ due to the change of the ambient temperature and the heat of the relay itself. Therefore, if the coil temperature increases, the operating voltage and the off voltage will also increase.

   3. The battery drive for automotive relays will cause the power supply voltage to decrease when the heavy load is turned on, which will affect the life of the relay. Pay attention to the impact of the power supply voltage fluctuation on the reliability of the relay.

   4. The maximum continuous applied voltage of the coil: In addition to the stability of the relay operation, the maximum continuous applied voltage of the coil is mainly limited by the insulation performance of the enameled wire. You should know the insulation level of the enameled wire of the product. In actual use, in the case of class F insulation at an ambient temperature of 40°C, the temperature rise limit may be considered to be a maximum of 115°C measured by the resistance method. However, due to the unevenness of the inner and outer rings, the recommended value is 105°C.

  1. Coil electrical corrosion: The automotive relay works for a long time in the environment of temperature and humidity circulation. When the coil is continuously connected to the positive pole of the power supply (disconnect the negative pole), the coil will be corroded and cause wire breakage, so the relay coil cannot be connected to high potential It must be ensured that the relay coil, moving reed and the positive pole of the power supply are disconnected.

   2. Precautions for using contacts

The contact is the most important part of the relay. The working reliability of the contact is affected by the contact material, contact voltage and current (especially the on and off voltage, current waveform), load type, on-off ratio, and environmental conditions. . Contact voltage: Inductive loads will generate a very high reverse voltage. The higher the voltage, the greater the energy and the accelerated contact corrosion and metal transfer. Contact current: The current when the contact is closed and opened has a great influence on the contact. When the load is a motor or headlight, the inrush current when closing is large, the loss of contacts and the amount of metal transfer are greater, the contact transfer will cause contact adhesion failure, and a confirmation test should be conducted. 1. Contact protection Reverse voltage: When disconnecting the inductive load of the relay coil series circuit or the motor, electromagnet and other inductive loads, surge absorption such as diodes must be used to protect the contacts. When the inductive load is disconnected, a reverse voltage of hundreds to thousands of V will be generated, which will aggravate the electrical corrosion of the contacts and reduce the service life. In addition, when the inductive load current is less than 1A, the arc generated by the reverse voltage decomposes the organic gas volatilized in the relay coil and the plastic, and generates black acid or carbon compounds on the contacts, resulting in poor contact. Contact metal transfer: Contact metal transfer is the transfer of contact material in one direction under the action of direct current. With the increase of the number of on and off times, the anode contact generates pits, and the cathode contact generates bumps. And the pit is easy to produce mechanical self-locking and cause contact adhesion. Anti-transfer contact materials or protection circuits should be used. Contact protection absorption circuit: using contact protection components or protection circuits can reduce the reverse voltage, but if it is not used correctly, it will have a negative effect.

   3. Precautions for using relay

   1. In order to prevent contamination of the terminal surface, the terminal should not be directly contacted, otherwise, solderability may be reduced.

   2. The position of the terminal should be

   is consistent with the hole position of the printed board. Any improper coordination may cause dangerous stress to the relay and damage its performance and reliability. Please refer to the hole punching diagram in the catalog for hole punching.

   3. After the relay is inserted into the circuit board, do not bend the lead out to avoid affecting the sealing or other performance of the relay.

   4. Do not apply excessive pressure to the relay casing during the insertion process to prevent the casing from rupturing or the operating characteristics from changing.

   5. The insertion and withdrawal pressure of the quick connection pin is 10 kgf. Too much insertion force will damage the relay, and too little pressure will affect contact reliability and current carrying capacity.

   6. It is particularly emphasized that if the relay is accidentally dropped or impacted during installation, although the electrical parameters are qualified, the mechanical parameters may change greatly, there are serious hidden dangers, and it should not be used as much as possible.

   7. Do not use silicon-containing resins and preservatives, which can cause contact failure, even for plastic-encapsulated relays.

   8. Pay attention to connect the coil power and the contact power according to the specified polarity. The contact is generally a moving spring connected to the positive electrode (+).

   9. Avoid the voltage applied to the coil exceeding the maximum allowable voltage or the temperature rise of the coil exceeding the insulation level of the enameled wire.

  10. The rated load and life are under the specified standard conditions, it is impossible to cover the various requirements for the use of automotive relays,

The actual load and life of the contact will vary significantly depending on the type of load, environmental conditions, operating frequency or other conditions. Please conduct a test or contact the relay manufacturer for technical support.

Inspection method of auto relay

(1) A simple method to judge the working performance of the relay

Turn on the ignition switch, and then use your ears or stethoscope to listen to the control relay for sound absorption, or feel the vibration of the relay by hand. If yes, it indicates that the relay is working normally. The failure of the electrical appliance is caused by other reasons. ; Otherwise, the relay is malfunctioning.

   can also unplug the relay for testing. For example, if the air conditioner compressor does not work, you can start the engine, and then turn on the blower switch and the air conditioner switch. Then unplug the connector of the air-conditioning compressor relay to judge. If the sound of the relay can be heard, and the engine speed drops significantly when the relay is unplugged, and the engine speed increases when the relay is plugged in, indicating that the relay of the air-conditioning compressor and its control circuit are normal.

   Regarding the position of the relay, all relays and fuse marked with a dotted line on the circuit schematic diagram are generally arranged in the central distribution box.

   (2) Common relay failures Common relay failure phenomena include: coil burnout, inter-turn short circuit (insulation aging), contact ablation, thermal decay, and failure to adjust the initial operating current.

   ① The relay coil is burnt out. In order to prevent this from happening, when performing repairs, maintenance, and electric welding, if the temperature may exceed 80°C, the temperature-sensitive relays and electronic control units should be removed.

  ② Contact ablation. For example, the relay of the air conditioner condenser fan of Jinbei Haishi car (using 491Q-ME engine), it is just below the glass cleaning spray pipe. If the spray pipe is broken, the cleaning fluid will leak to the relay, making the relay normally open Corrosion of the contacts can not be opened, which will cause the failure of the fan of the air conditioner condenser to rotate constantly. Therefore, water ingress of the relay should be strictly prevented.

   (3) Try to reduce the contact resistance of the relay contacts

   The contact resistance between the relay contacts of the vehicle is mainly composed of two parts: shrinkage resistance and surface film resistance. The contact resistance of the contact is related to the contact form, material properties and surface processing of the contact. It can be seen from this that to reduce the contact resistance of the relay contacts, under a certain contact pressure, it is possible to start by improving the contact state and improving the contact materials.

(4) Poor ECU grounding may affect the normal operation of the relay. In a Shenlong Fukang 988 car, during normal driving, the engine will automatically shut down and start again, unable to get into the car. Turn on the ignition switch, you can’t hear the sound of the fuel pump running, and there is no high-pressure fire. Check the ignition coil and find that there is no power on the plug, but the resistance of the primary side and the secondary side are normal. Measure the injection double sealed relay of this car, its plug has 12V power supply. There is no high-pressure fire and no sound of relay pull-in when replacing the double-sealed relay. Use a wire to directly connect the No. 10 foot of the double-sealed relay to the sound of the relay. The engine can also be started successfully. But the strange thing is that after dismantling this ground wire, the engine does not turn off, and after turning off the ignition switch and restarting the engine, it is normal. Analysis of the reason, this is due to poor grounding of the engine ECU, resulting in a low supply voltage of the relay coil (sometimes only about 2V), it is impossible to make the relay pull in. After directly connecting the ground with the wire, the relay has a voltage of 12V, so it pulls in smoothly, so the engine starts successfully. After removing the temporary ground wire (the ignition switch is still in the on state), the relay still has a lower holding voltage (this is a common feature of the relay). Even if this holding voltage is only 2V, the relay will not break. On, so the engine does not shut down. When the ignition switch is turned off, the self-induced electromotive force generated by the circuit is much higher than the power supply voltage. Under this strong electromotive force, the poorly grounded ground may return to normal, so the engine is normal after starting. However, the above faults will be reproduced, so the way to eradicate is to deal with the parts with bad grounding thoroughly

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