The warning lights are not installed in your car for fun. What does the check engine light mean?
A car is a great thing. Thousands of small parts work together precisely mile after mile, and in return the driver only has to ignore a warning light every now and then. It should be obvious that this is not a good idea, because the warning signals are not placed on the dashboard by chance. Anyone who ignores the emissions control light is not necessarily in acute danger, but the longer the light burns, the more damage the engine suffers. PKW.de tells you what’s behind the light, what it can mean and what to do when the dashboard lights up for the first time
Why is the engine control light on?
Where there are many moving parts at work, there are also more sources of error. Car manufacturers place a multitude of sensors in their cars that monitor the condition of the vehicle every second. The temperature of water, motor oil and exhaust is recorded, as is the carbon monoxide content of the exhaust gases, the air pressure in the engine and many other data points. A small computer evaluates this data and adjusts when necessary. Sometimes, however, the computer detects a fault that is not so easy to correct. Then an error code is written to the computer’s memory and a little light in the shape of an engine comes on on the dashboard. This is the emission control light, probably the most ignored light signal in history.
The engine control lamp, abbreviated MKL, is designed to detect errors in the engine control system. It may illuminate steadily or flash. Their color may be yellow or red, depending on the model of the vehicle, and also depending on the severity of the fault. The service booklet tells you which colors are possible and what the glow or flashing means.
A less serious defect does not affect the engine directly, but auxiliary systems (e.g. the exhaust system). In this case you should take the machine to a workshop as soon as possible and have it checked.
A serious defect is directly related to the engine itself (e.g. malfunctions in the cooling system). In this case, it is better not to drive the car further and, if necessary, have it towed.
If the check engine light comes on briefly and then goes out again, there is usually nothing else to do. It is normal and intentional for the MKL to light up briefly when starting. If, on the other hand, it briefly lights up while driving, it is probably due to a temporary error (such as an incorrect lambda probe value) that has disappeared on its own.
Defective EGR valve
If the EGR valve is defective, the engine control lamp starts to light up or flash. A defective EGR valve does not have to be replaced immediately, but you should not wait too long to do so, otherwise there is a risk of damage to the turbocharger.
Other symptoms: loss of power at full throttle, starting problems, jerking when driving, smoke from the exhaust, increased fuel consumption.
Thermostat is open and stuck
Even if the thermostat is stuck in the open state, the MKL reports. If the problem is not corrected over a longer period of time, consequential damage can occur: If the engine does not warm up properly, the mechanical components adapted to a certain operating temperature wear out quickly. Since the engine does not leave the warm-up phase, it also runs permanently too rich and consumes more fuel.
Other symptoms: cooling water temperature does not rise, heating does not warm up.
Clogged diesel particulate filter
The MKL can also indicate a clogged diesel particulate filter (also called a soot particulate filter). This wouldn’t be an emergency, but if you don’t clean or replace the DPF over a long period of time, the car may eventually stop running.
Other symptoms: loss of power, newer vehicles you get a corresponding message in the display.
Defective glow plug
In newer cars, a diagnostic device can be used to determine which glow plug is affected by a defect. However, if you ignore the check engine light and the many other symptoms (see below) over a longer period of time, you run the risk that the car will no longer start.
Other symptoms: smoky start, nail-biting start, long battery-exhausting start with strong odor, engine runs hard and out of round.
Clogged fuel filter
The MKL may also light up or flash when the fuel filter is clogged. If the signs are ignored, the filter can become completely clogged over time with the result that the car will eventually not move at all.
Other symptoms: Engine starts poorly or not at all, or dies off while driving, engine performance decreases, car jerks when accelerating.
Defective lambda sensor
Whether the engine control lamp flashes or lights up because of the lambda sensor can only be determined with a diagnostic device. If it really is the lambda sensor and the problem is not rectified, the catalytic converter or the soot particle filter may be affected.
Other symptoms: rough idling when the engine is warm, increased fuel consumption, car does not pull properly, in the case of diesel engines: black smoke from the exhaust.
Clogged or leaking injector
If the check engine light is on or flashing because of a clogged injector, there is no need to declare an emergency right away, but if you do nothing, the injector will eventually clog completely and the car won’t move.
Other symptoms: Car starts badly or not at all, engine runs out of round, increased fuel consumption, bad exhaust values, car does not pull properly, metallic knocking when driving, black smoke from the exhaust.
If the MKL lights up or flashes because of the ignition system, you should not hesitate for long. Because if the ignition system is no longer working properly, at some point the car may not start or even go out while driving.
Other symptoms: Car jerks when stationary, stuttering and misfiring.
If the check engine light lights up or flashes because of a fault in the cooling system, there are several possible causes: the water pump may be defective, the hose may be leaking, the cylinder head gasket may be porous (exhaust gases enter the cooling system). As a result, the engine becomes too hot and the MKL starts to light up. If the check engine light is on because of a fault in the cooling system, action should be taken as soon as possible and the car taken to the workshop. After all, in the worst case, piston seizure is imminent.
Other symptoms: The engine does not come up to operating temperature or rises too high, in case of water loss white smoke comes out of the exhaust.
Defect in the mass air flow sensor
The somewhat inconspicuous mass air flow sensor can also cause the engine control lamp to flash or light up. It is used to determine the correct fuel injection quantity by measuring the air flowing through it, its temperature and its humidity, and transmitting the values to the engine control unit. A defect is particularly noticeable at low engine speeds. In the long run, the catalytic converter or the soot particle filter may be damaged.
Other symptoms: The car does not pick up the throttle and jerks.
Defective throttle valve
An illuminated or flashing engine control light can indicate a mechanical (throttle valve hangs), but also an electronic defect (throttle valve does not take the correct position and does not pass on the correct amount of air). As with a faulty lambda sensor, if the damage is not repaired, the catalytic converter or soot particle filter may be affected.
Other symptoms: The car takes the gas badly, jerks when driving or simply dies off when shifting into neutral.
Defective engine control
Sometimes there is also a problem in the engine control system. If the timing chain is elongated, the camshaft sensor and crankshaft sensor send different signals to the engine control unit. Consequence: The MKL lights up or flashes. If the defect is in the camshaft or crankshaft sensor itself, either an incorrect signal or no signal at all is transmitted. In this case, the MKL also starts to flash or light up. In both cases, action should be taken quickly before the car switches to the emergency running program.
Other symptoms: Engine speed fluctuates at idle, car jerks.
How is the error found?
The good news is that if the little light is only on, all is not lost. You can get home or to the nearest garage in any case, and usually it is still enough to use the car normally until you get a workshop appointment. Before the mechanic then takes a look under the hood, high-tech is first used: a laptop is connected to the engine control unit with a special adapter, the so-called OBD port. This allows the fault codes to be read out and analyzed by the computer. The advantage: In the best case, the mechanic does not have to disassemble the entire car into its individual parts to find the fault, but can go in search of the defect in a targeted manner. Afterwards, a connection with the engine control unit is established again and the codes are deleted. Now the engine control light is also off.
What does the glowing of the engine control light mean?
An illuminated engine control light can have many different reasons. They range from “Differential pressure in the soot particle filter for cylinder bank 1 is too high” to “Lambda sensor temperature too high”. Most of these faults, as mentioned, are not that dramatic. But if the check engine light starts flashing, then you have a problem, because that indicates a serious fault that can massively endanger not only your car, but also your safety. Turn the car off at the earliest opportunity and only drive it if it really can’t be avoided, and even then only slowly. A repair is in most cases far cheaper than a new car. That’s why it’s better to go to the workshop than to the car dealer.
The engine light is on. What can I do right now?
Now good advice is expensive. Since it performs monitoring functions, this is the first place to start. Now you can first check for yourself what is obviously wrong. So turn off the ignition, open the hood and check the line and cables to the air flow meter or that go to the exhaust gas recirculation valve. This means both the hoses, lines and electrical cable paths. These may be torn, brittle or bitten by martens. Be careful if your engine is still hot.
But it is also possible that your air flow meter is contaminated, your soot particle filter is clogged or there is another fault. If the error is not easy to find, you can easily read it with your own diagnostic device and fix it. Or contact your workshop or act according to the detailed operating instructions. But do not ignore the display! This can possibly mean an irreparable total failure of the drive.