Cars

Check engine light: This is why the MKL lights up or flashes yellow

The check engine light, or MKL for short, is one of numerous warning and indicator lights in a car’s instrument cluster. It glows yellow or orange and its shape symbolizes an engine block. If the car is operating correctly, it will only come on when you turn on the ignition – after starting the engine, it should go out again after about three seconds. There is only a fault if the check engine light also lights up or flashes while driving.

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Check engine light is on: what to do?

If the check engine light also comes on or flashes after the engine has been started or while driving, you should drive the car to the workshop as soon as possible to have the error memory read out and thus find out the cause of the error message. Normally, however, the car does not have to be stopped immediately and the engine switched off.

However, it is possible that the car switches to emergency engine operation at the same time (emergency driving program). Only reduced engine power is then available, but this is sufficient to drive to a workshop. But even if the emergency program is not activated and the car apparently continues to run normally, you should not ignore an illuminated check engine light. Otherwise there is a risk of expensive consequential damage (e.g. to the catalytic converter).

On the other hand, you should stop as soon as possible if the oil pressure warning light comes on while driving. In this case, drive to the nearest safe parking space, switch off the engine and check the oil level!

Check engine light flashing: what does that mean?

A check engine light can either stay on or flash. The constant illumination is a sign that a fault has been stored in the on-board diagnosis fault memory. There is no immediate danger to the engine, but the cause of the fault should soon be identified and eliminated in the workshop. Gentle driving is recommended. On the other hand, if the check engine light flashes quickly, this is a sign that a serious fault has been detected. The defect should be repaired as soon as possible to avoid consequential damage. This flashing occurs, for example, in the event of ignition misfires or combustion misfires.

Check engine light is on or flashing

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The check engine light comes on when the ignition is switched on

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Check engine light does not come on when ignition is switched on

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Check engine light stays on continuously

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Rapid flashing of the check engine light

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An error was stored in the error memory. There is no immediate danger to the engine.

A fatal error was detected.

Have the lamp replaced

Visit a workshop as soon as possible, have the fault memory read out, rectify the defect if necessary

The defect should be repaired as soon as possible to avoid consequential damage


What is the cause behind the MKL lighting up?

The causes behind a glowing check engine light are numerous, and there is not always a serious problem behind it. Many components can be affected, such as the swirl flaps in the intake tract, which no longer move due to a broken actuating mechanism (error message, for example, “Target value not reached”). Or sensors such as the air mass meter or the lambda sensor(s) measure values ​​that are outside the valid parameters.

Leaks in the intake or exhaust system can also be detected using pressure sensors. With the help of the crankshaft and camshaft sensors, the on-board diagnosis even detects combustion misfires in the individual cylinders by calculating the angular speeds of the crankshaft. This allows fuel injection to be selectively suspended to protect the catalytic converter from damage.

How much does it cost to read out the error memory?

Workshops have the appropriate diagnostic devices and usually offer to read out the error memory at prices between 25 and 80 euros. Since the process takes less than 30 minutes, the reading can usually be carried out at short notice and in some cases without prior appointment.

Some workshops reimburse the customer for the cost of reading out the error memory after placing a repair order. ADAC members have the option of having the fault memory read out at ADAC locations and partner workshops at a reduced cost. These differ depending on the regional area. In Hamburg, for example, 25 euros are due for this; if you are not a member of the ADAC, you pay 35 euros.

Can you read the fault memory yourself?

If you own an OBD2 diagnostic device, you can also read out the fault memory yourself. The devices are already available at prices starting at around 20 euros. You should make sure that the diagnostic device is compatible with your own vehicle. Cars from the Volkswagen Group use, for example VCDS (VAGCOM DdiagnosticSsystem) and thus a different diagnostic software than cars from BMW or Mercedes (more on OBD2 diagnostic devices).
However, some general parameters can be read with most standard diagnostic devices on all OBD2-capable cars. An alternative to diagnostic devices are smartphone apps that work in conjunction with an adapter. The adapter is plugged into the OBD2 socket and connects to the app on the smartphone or tablet via Bluetooth. The most well-known diagnostic app is the Carly app. One advantage of the app: it is available specifically for different brands.

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In general, nothing speaks against the purchase of a diagnostic device or a diagnostic app. However, it should be borne in mind that most diagnostic devices do not spit out any specific repair instructions for eliminating the cause of the error. In other words, interpreting the error log is often difficult for laypeople.

Can you turn off the check engine light yourself?

Many errors stored in the error memory can also be deleted with an OBD-2 diagnostic device. Hobby screwdrivers like to carry out this experiment as a first measure. The annoying yellow lamp is finally off again and your conscience (temporarily) calmed down. In some cases, the error actually no longer appears after deleting it.

However, the check engine light is usually permanently on again after a short drive, namely as soon as the diagnostic system has recognized the error again. In the long run, it only helps to fix the underlying defect and thereby prevent consequential damage at the same time.

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