Mercedes BAS ASR ABS Light ON

BAS / ASR and ABS lights staying ON in your Mercedes-Benz? This article will show you how to troubleshoot BAS/ASR light problems. What ASR, BAS, and ABS lights mean. Common problems and possible solutions.

Common Mercedes BAS & ASR Problems

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• ABS/ ASR/ BAS Fault Codes
• BAS/ASR Light Stay On Instrument Cluster
• Mercedes goes into limp mode, stuck in gear

What do ABS BAS ASR lights mean? 

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If any of these lights turn on and stay ON once you start to drive the car, it means there is a problem with one of the following systems or related sensors.

• ASR Light Meaning – Anti Slip Regulation / Acceleration Skid Control
• BAS Light Meaning – Brake Assist System
• ABS Light Meaning – Antilock Brake System

Troubleshooting BAS ASR ABS Lights

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Step 1: Ensure that the main battery on your Mercedes-Benz is holding a proper charge. Mercedes-Benz cars are very sensitive to low voltage. An old battery can cause BAS/ASR lights to stay on. It is common for BAS / ASR lights to come on with a dead battery. It takes a while for a discharged battery to charge fully. Your Mercedes-Benz battery should have its manufactured date stamped on top or the side. If your battery is over ten years old, consider replacing it even if the car has been starting fine. Don’t wait until your Mercedes battery is completely dead.

If you need a reasonably priced Mercedes battery, read this article: Top 5 Batteries for Mercedes-Benz.

Step 2: Check the brake light switch. The brake light switch is probably one of the main causes that trigger BAS/ASR light problems. The switch doesn’t only turn on the brake lights on the rear, but other systems, including ABS, ASR, and BAS, use the input from the switch.

To check if the brake light switch is the problem, pay close attention when the BAS/ASR lights come on.

Do ASR/BAS lights come on when you press the brake pedal?

If the ASR/BAS lights come on when you push the brake pedal, the brake light switch is most likely the problem.

It is not worth repairing the original brake light switch. Since the brake light switch is relatively cheap (check prices on Amazon) and often the main problem is it is better to replace it. Replacing the brake light switch is easy. Watch the following video on changing the brake light switch on a Mercedes-Benz.

 

Step 4

If you replaced the brake light switch and are still having problems with the BAS/ASR lights, the next thing to check would be the ABS wheel speed sensors. They are installed on two (diagonal) or all four-wheel knuckles and measure wheel revolutions.

How do you know that the ABS sensors are defective?

The best way to diagnose an ABS sensor would be to use a diagnostic scanner such as the YOUCANIC full system scanner. Note that you need a full system scanner, and an OBD-II scanner can only diagnose the check engine light and will not read/erase codes related to ABS/BAS/ASR. You can click here for a comprehensive guide.

Let’s say you don’t have such a scanner or can’t invest in one yet.

Here is a tip for you. Pay close attention at the moment your BAS/ASR lights come on.

Do the BAS/ASR lights come on when you start driving but not when you press the brake pedal? 

Typically, this happens when one of the ABS sensors is defective. The BAS/ASR light usually comes on when you exceed five mph.

Step 5

Check the rear brake lights. Do they work properly? Does the third brake light work? It is not common for a short to develop in the brake light circuit and cause such problems. Unplug the rear brake lights and check for corrosion if the rear brake lights don’t work. Check the connections that plug into the brake light assembly. You may want to use a digital multimeter to check continuity or to ensure there is no short. In a few cases, we have seen wires inside the headlight & tail light fried and causing shorts and malfunctions.

Conclusion

We hope one of this article’s tips will fix your BAS/ASR light problem. Check the brake light switch, car battery, and ABS wheel sensors.  If you still have BAS/ASR light problems, it may be time to have an auto mechanic or a Mercedes-Benz dealer perform a diagnostic. Or, if you are a DIYer, use the YOUCANIC full system scanner to run a diagnostic yourself.

If you want to figure out the BAS/ASR problem on your own, you will need to get a hold of an advanced diagnostic scanner to do a complete system scan and read the fault codes. The error codes will give you a good idea of the cause of BAS/ASR lights staying on. Other possible problems triggering the BAS/ASR light are a defective SAM module, bad ECU, or ABS module.

A YOUCANIC full-system diagnostic scanner can help you troubleshoot Mercedes-Benz problems by interpreting fault codes, performing diagnostic tests, and resetting maintenance reminders. This tool provides valuable information for informed decision-making on repairs and maintenance, making it a powerful asset for DIY mechanics and professional technicians.