What are the common faults of automobile instruments?

What will happen if the car instrument is broken? Let's take a look at Bian Xiao's sharing today.

A, oil pressure gauge fault

1, various engine speeds, and the oil pressure gauge has no pressure indication.

Cause of failure: the power cord of lubricating oil pressure gauge is broken; The electric heating coil in the lubricating oil pressure gauge is burnt out; Lubricating oil pressure sensor is damaged; Engine lubrication system failure.

Fault diagnosis: Turn on the ignition switch, remove the lead at one end of the lubricating oil pressure sensor, and conduct instantaneous grounding test. If the pointer of lubricating oil pressure gauge moves to the direction of 0.5MPa immediately, it means that the lubricating oil pressure gauge is good; At this time, you can remove the sensor and install the removed wire, and insert a nail without a sharp point into the oil hole of the sensor to press the diaphragm. If the lubricating oil pressure gauge moves, it means that the sensor is good and the engine lubrication system is faulty; Otherwise, the sensor is faulty and can be properly repaired.

If the lead at one end of the sensor is grounded and the lubricating oil pressure gauge still does not move, one end of the test lamp can be connected to the power terminal of the oil pressure gauge, and the other end can be grounded for testing. If the test light is not on, the power cord is disconnected; If the test light is on, it means that the lubricating oil pressure gauge itself or the wiring of the sensor is faulty. At this time, the grounding test can be carried out at one end of the lead-out terminal of the lubricating oil pressure gauge. If the pointer moves normally, it means that the wire from the instrument to the sensor is open. Otherwise, the watch itself is damaged.

2. After turning on the ignition switch, the engine does not start, and the pointer of the oil pressure gauge points to the maximum value.

Cause of failure: the oil pressure gauge is grounded to the sensor wire; Internal ground of the oil pressure sensor.

Fault diagnosis: in this case, turn off the ignition switch immediately to avoid the pressure gauge burning out; During inspection, the wire at one end of the sensor can be removed first, and then the ignition switch is turned on for testing; If the pointer does not move, it means that the sensor is short-circuited internally and should be replaced or repaired. If the pointer still points to the maximum value, check and repair the grounding of the pressure gauge to the sensor line.

3. When the engine rotates at various speeds, the pointer of the oil pressure gauge is placed at will, and the indication is not allowed.

Cause of failure: the pressure-sensitive diaphragm of the oil pressure sensor is deformed due to excessive force; Ablation and oxidation of internal contact surface of oil pressure sensor; The connecting wire is in poor contact.

Fault diagnosis: turn on the ignition switch and check whether the terminal is rusty or loose and whether the wire is open; If yes, it should be repaired, otherwise, the sensor should be removed and installed on the oil pressure test bench to test the accuracy of its indication. If the difference exceeds 20%, replace the sensor.

Second, the water thermometer fault

1. After the ignition switch is turned on, the pointer of the water thermometer does not move, even if the water temperature changes, the pointer still does not move.

Cause of failure: the power cord of the water thermometer is open; The electric heating coil of the water thermometer is burnt out; The hot wire coil of the water thermometer sensor is burnt out; Poor connection or open circuit between thermometer and sensor wire.

Fault diagnosis: after the ignition switch is turned on, remove the lead wire at one end of the water temperature sensor and directly ground it with parts such as cylinder body. If the pointer of the water thermometer returns to normal immediately, it means that the water thermometer is good, indicating that the electric heating coil of the sensor is burnt out or has poor contact; If the pointer of the thermometer is still fixed, one end of the test lamp is grounded and the other end is connected to one end of the thermometer power terminal. If the test light is on, it means that the thermometer itself or the circuit from the thermometer to the sensor is faulty, otherwise the electric heating coil inside the thermometer is burnt out and the circuit is open. If the test light is not on, the power cord will be disconnected. At this time, the working performance of other instruments should be checked, and then eliminated or replaced according to the specific situation.

2. After turning on the ignition switch, the engine has not started, or the pointer of the water thermometer points to the maximum value shortly after operation.

Cause of failure: somewhere between the thermometer and the sensor wire is grounded; The sensor is internally grounded.

Fault diagnosis: Turn on the ignition switch, and remove the wire at one end of the sensor for grounding test. If the pointer returns to its original position, it means that the sensor is grounded internally; Otherwise, still use disassembly method to check whether there is grounding on the lead from thermometer to sensor, and then repair or replace it.

Three, ammeter fault

1, after the engine is started, no matter how much the engine speed increases, the ammeter pointer indicates discharge.

Cause of failure: the fan belt is too loose, broken or slippery with oil; Generator wire connector is loose, poor contact or wire grounding short circuit; The generator cannot generate electricity; The external excitation circuit is disconnected; Improper adjustment of regulator, loose connector, or contact ablation and resistance burning; The battery plate is vulcanized, and the electrolyte density is too low.

Fault diagnosis: first, distinguish whether the battery is not charged because of insufficient storage capacity or charging system failure. If it is caused by the fault of the charging system, first check whether the fan belt is slipping or loose, whether the connecting cable is connected well and whether the generator is connected correctly.

After the engine stops, remove the wires from the regulator armature and the magnetic field terminal, and connect the two wire ends. Start the engine, keep idling, and observe the ammeter. If the regulator is charging, it means that the low-speed contact is ablated, dirty or the high-speed contact is inseparable. When you touch the ignition switch, you can usually hear a click. If there is no "click" sound, the relay contact is not closed. Remove the regulator cover.

When that wire on the armature and the magnetic field terminal on the regulator are remove and connected, the engine is star to idle; If there is no charging, stop the engine, remove the lead wire connecting the armature terminal of the generator, and use the small light bulb of this vehicle as the test lamp, one end of which is connected to the armature terminal of the generator and the other end is connected to the shell; If the test light is on, it means that the generator is in good condition and the charging circuit is faulty; If not, it means that there is a fault inside the generator and the generator should be disassembled; Check whether the diode is intact, whether the insulation between the terminal and the slip ring is damaged or broken, whether the stator and rotor coils are open or short-circuited, and whether the brush is in good contact with the slip ring.

2. After starting the engine, the ammeter pointer indicates that the charging current is higher than 10A.

Cause of failure: improper adjustment of the contact gap of the regulator and high regulating voltage; The regulator magnetic coil resistance is open; Short circuit inside the battery; The first pair of contacts of the regulator is ablated, or the second pair of contacts is dirty and has poor contact.

Fault diagnosis: Remove the regulator cover and check the first pair of contacts. If ablation occurs, it should be disconnected. If yes, increase the engine speed and check whether the second pair of contacts can be closed. If it can be closed, it is considered that the second pair of contacts is in poor contact. If it doesn't close, test the suction force of the coil core with a screwdriver. If it is suction force, it is an open circuit of the coil temperature compensation resistor; If the suction force is small, it is a discontinuous path of coil turns; If the suction force is strong, the spring tension of the movable contact arm should be reduced. If the charging current is normal, it is caused by excessive spring tension.

3. When the engine is at various speeds, the indicated value of ammeter is too small, especially after turning on the light at night, it is difficult to start the engine.

Cause of failure: the fan belt is too loose; Poor connection of charging cable; Individual diode of generator is damaged or brush contact is poor; The regulating voltage of the voltage regulator is too low or the contacts are dirty and ablated; The first phase of the generator stator winding is in poor contact, or short circuit or open circuit.

Fault diagnosis: firstly, check whether the fan belt is unblocked and the wire connection is good. If they are all good, remove the regulator cover, tighten the spring by hand, and start the engine at medium speed. At this time, if the charging current increases, the limit voltage of the regulator is low, and the spring tension should be tightened. If the charging current is still small, connect the first pair of contacts with a screwdriver. At this time, if the charging current increases with the increase of engine speed, it indicates that the first pair of contacts are ablated or dirty and should be repaired or cleaned. If the charging current is still small, it is an internal fault of the generator and should be removed for maintenance.

4. When the engine runs at a speed higher than the idle speed, the ammeter pointer swings left and right, indicating unstable charging.

Cause of failure: the fan belt is too loose; Bad wiring between battery and generator armature terminal wire; Poor connection, open circuit or short circuit of internal wires of the generator; The generator carbon brush is seriously worn or the spring pressure of the carbon brush is too small, or the slip ring is dirty and has poor contact; The contacts of the voltage regulator are ablated or dirty, and the spring tension is weak or the additional resistance is unreliable.

Fault diagnosis: firstly, check whether the fan belt is too loose and whether the wires are well connected; Then remove the regulator cover, tighten the spring by hand, and start the engine to run at medium speed. If the charging is stable, it means that the spring tension is too small and should be adjusted. If the charging is unstable, connect the first pair of contacts with a screwdriver. If the charging is stable at this time, it means that the contact ablation or additional resistance is unreliable. Reduce the engine speed and stop the first pair of contacts. If the charging is stable at this time, the additional resistance is unreliable. If the charging is unstable, it is the contact. If the first pair of contacts connected with a screwdriver is not charged stably, it means that the fault lies in the generator. Check whether the contact between generator carbon brush and slip ring and the connection of internal wires are good.

Fourth, the fuel gauge is out of order.

1, after turning on the ignition switch, no matter how much oil is stored in the fuel tank, the pointer of the fuel gauge always points to 1 (full of oil).

Cause of failure: open circuit from fuel gauge to sensor wire; Sensor internal open circuit.

Fault diagnosis: Turn on the ignition switch and remove the terminal wire of the fuel gauge sensor for grounding test. If the pointer is 0, it means that the sensor is open internally; If it still does not point to 0, the oil meter can be led out for grounding test. If the pointer points to 0, it means that the fuel gauge is open to the sensor wire and can be repaired as appropriate.

2. Turn on the ignition switch, and the indicator of the fuel gauge always indicates 0, but in fact the fuel tank is not oil-free.

Cause of failure: internal grounding of the sensor; Buoy damaged; The polarity of fuel gauge terminal is reversed; The fuel gauge power cord is open.

Fault diagnosis: check whether the wire connection is good. If the wires are well connected, remove the wires from the sensor for grounding test. If the pointer rotates normally at this time, it means that there is grounding inside the sensor or the buoy is damaged, and it should be removed for maintenance.

Five, the speed odometer fault

1, the speedometer pointer always points to zero while driving, and the odometer does not count.

Cause of failure: the connecting nut of the speedometer flexible shaft is not tightened; The flexible shaft of speedometer breaks or falls off; The driving pinion of speedometer is damaged; The speedometer is broken.

Fault diagnosis: check whether the flexible shaft is in good condition. If it is damaged, it should be replaced. If it falls off, it can be reinserted and tightened. At the same time, check whether the driving gear is damaged, and replace it if it is damaged; If all the above are good, the speedometer is damaged and should be replaced.

2. During driving, the speedometer pointer keeps swinging, and sometimes it will jump.

Cause of failure: improper installation of the lock nut of the speedometer flexible shaft; The steel wire mandrel of the speedometer flexible shaft is twisted; The speedometer is broken.

Fault diagnosis: firstly, check whether the lock nut of the speedometer flexible shaft is installed correctly; Secondly, remove both ends of the flexible shaft and screw both ends of the mandrel by hand. If the resistance is felt and the steel wire mandrel is bent, a new mandrel or flexible shaft should be replaced; If the resistance is uniform and there is no sense of sticking, check whether the dial of the odometer is issued. If it is released, it should be replaced. Otherwise, replace the speedometer.

3. The pointer only swings slightly at high speed, often points to zero at medium and low speed, or the pointer index is too large at medium and low speed, so the indication is not allowed.

Cause of failure: loss of excitation of permanent magnet; Hairspring deformation; The hairspring has lost its elasticity.

Fault diagnosis: If the pointer hardly moves when driving at medium or low speed, the speedometer can be removed, the rotor can be taken out and re-magnetized; If the pointer value is too large, replace the hairspring.

Expand small knowledge

Automobile instrument assembly

Automobile instrument assembly is the instrument area in front of the steering wheel, including speedometer, tachometer, water thermometer, fuel gauge and odometer. Nowadays, many cars also have information screens to keep track of all kinds of information of vehicles, such as inside and outside the car, fuel consumption and so on. This whole accessory is called instrument assembly.

Most instrument groups are composed of masks, frames, watch cores, printed circuit boards, connectors, alarm lights and indicator lights. Some instruments also have voltage regulators and alarms. The number of instruments in the instrument cluster of different cars is different, and there are many indicator lights, alarm lights and instrument lights on the instrument panel.

Fault inspection method of automobile electronic instrument

The damage of automobile instrument assembly is due to loose line plug or blown fuse. When it is found that the automobile instrument assembly is broken, the first task is to detect whether it is caused by a broken fuse, and then exclude the detection of light bulbs, and finally detect the wiring of the automobile.