The phenomena of car malfunctions vary in a thousand ways, and operation of each system affects each other. Some malfunction phenomena may be caused by another malfunction. In face of complex vehicle failures, maintenance personnel need to determine which are normal and which are abnormal, and not treat normality as a "disease". They need to be tested in conjunction with structure and principle.
Interpreting automotive indicator signals
(l) Oil pressure warning light.
If engine oil pressure warning light is on when engine is running, it means that oil pressure in main oil passage of lubrication system is too low. There may not be enough oil in oil pan, or lubrication system has a significant failure. At this time, it should be stopped for inspection and repair.
However, it is normal for oil pressure warning light to come on when engine is running at a standstill and then go out as the engine speed increases.
(2) Charging current indicator.
Some models use an ammeter instead of a charging indicator. Under normal conditions, as long as technical condition of battery is normal, after engine has been running for a certain period of time, charging current indicated by ammeter will decrease until it approaches 0, indicating that battery is fully charged. which is normal. To make sure charging system is OK, you can turn on headlights and let battery short out
Discharge at a certain time, and then start engine. If charging current increases at this time, it means that charging system is basically normal;
(3) ABS warning light.
If vehicle is not operated for several hours, pressure in hydraulic system will drop even further.
The ABS warning light and brake warning light may be on for more than 20 seconds. This is normal because ABS hydraulic pump and its electric motor take a certain amount of time to restore oil level in pressure accumulator. to normal pressure. In addition, ABS must rely on normal braking system
The platform is what matters. Therefore, in following cases, brake warning light comes on even if ABS system is normal.
①Only drive wheels rotate, such as when lifting vehicle for various idle tests, because some wheels do not have speed.
It is normal for a new ABS warning light to come on.
②One drive wheel is jammed.
③③The wheels are spinning.
④ ABS has been working for a long time.
⑤The electronic signal affects wheel speed sensor.
2. False conclusion about car noise
(l) Gasoline engine noise.
Severe deflagration in cylinder not only greatly increases noise of a gasoline engine, but also easily causes piston and valve ablation, shortening engine life. But for a conventional gasoline engine, when load is large and maximum torque speed is close, a slight deflagration sound of gasoline engine is normal, indicating that ignition timing of engine is adjusted more accurately.
(2) Engine noise.
Some large trucks tow four-wheel trailers, most of which use air brake systems, so an air compressor (commonly known as an "air pump") is fitted to vehicle. Most of excessive noise of large trucks comes from air compressor. On one hand, this is noise from operation of transmission belt of air compressor (you can temporarily remove transmission belt to check to see if butterfly sound changes); Cascade clutch, this type of dog clutch can withstand a lot of shock when combined, and when worn, it will make a distinct noise. Maintenance personnel should not confuse noise of an air compressor with sound of an engine.
(3) Noise when using starter fluid.
In alpine regions, traditional diesel engines are often difficult to start in morning and sometimes require use of starting fluid. However, at time of starting with starting fluid, engine will make an unpleasant sound. This is normal. This is not an engine malfunction, but sound of a sudden burning of starting fluid in cylinder, and it will return to normal after starting.
3. Distinguishing Multiple Phenomena
(1) "Add water to radiator and it will fill immediately."
Pouring water into radiator will immediately fill it. In fact, two situations are possible: one situation, there is really enough water in cooling system, and there is no need to add too much water; other situation is that cooling system is seriously lacking water. However, because operator poured water into radiator too quickly, air in cooling system was blocked in water jacket, forming an "air lock" and not being able to escape. is an illusion. The correct way to add water is to pour water several times to let air out of water jacket and, if necessary, unscrew water release switch on cylinder block to release some of air.
On other hand, when ambient climate and workload are basically same, if volume of water in engine radiator becomes less and less, you should not take it lightly. It is possible that scale in cooling system has thickened or accumulated Too much pollution causes volume of cooling system to become smaller and smaller. At this time, cooling system should be thoroughly cleaned, and coolant flow rate should not be rashly counted.
(2) "Insufficient rubber tire pressure".
Many vehicles use radial tires with excellent performance. As a rule, radial tires take up a larger area than conventional diagonal tires. Some people think that tire pressure is not enough, so constant inflation often leads to over-inflation and shortens life of a radial tire.
On other hand, when air pressure in a radial tire is really not enough, you can't take it for what it is and neglect to inflate it. It is best to use a tire pressure gauge to check if air pressure in a rubber tire is correct.
(3) "Water is coming out of engine exhaust".
This phenomenon is more obvious when driving at low speed on busy roads and in winter. Some people think that there is a problem with a leak in engine. In fact, this is a normal physical phenomenon, which is a manifestation of complete combustion of fuel.
The combustion of automotive fuels mainly produces carbon dioxide, water and a small amount of carbon monoxide. After each 1 kg of gasoline is mixed with air, about 1.42 kg of water is formed, which is mainly emitted into atmosphere as steam. Since main muffler is located at rear of car, it has a multi-chamber structure and temperature is relatively low. When water vapor is cold, it will form accumulated water. This accumulated water will be discharged under pressure of high-speed airflow, forming common phenomenon of running water.
If sulfur content of fuel is too high, after combustion, sulfur-containing chemicals will be formed, which will chemically react with water to form acidic substances, which will easily lead to corrosion and breakdown of muffler. If you park your car uphill. Start engine and give it a quick shake to help drain any accumulated water and prolong muffler life.
(4) "Hydraulic lifting system slowly raises."
When hydraulic lifting system is used for first time, design allows for "creep" phenomenon, but after temperature of hydraulic oil rises after hydraulic lifting system is fully integrated, hydraulic lifting system still appears. "crawl", indicating that hydraulic lifting system. If there is a leak or blockage, the fault location must be found in time.