BAS / ASR and ABS lights staying ON in your Mercedes-Benz? In this article, we will show you how to troubleshoot BAS/ASR light problems. What ASR, BAS, ABS lights mean. Common problems and possible solutions.
Common Mercedes BAS & ASR Problems
- 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?
If any of these lights turns 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
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 be the primary cause of BAS/ASR lights staying 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 the date it was manufactured 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 cause that triggers BAS/ASR light problems. The switch doesn’t only turn on the brake lights on the rear, but the input from the switch is used by other systems including ABS, ASR and BAS.
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 as soon as you press the brake pedal?
If the ASR/BAS lights come on as soon as 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 it is better just to replace it. Replacing the brake light switch is easy. Watch the following video on how to change the brake light switch on a Mercedes-Benz.
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 iCarsoft MB II (works only on Mercedes-Benz cars) or Autel DS708 (works on almost all car brands). 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.
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 as soon as you start to drive but not necessarily when you press the brake pedal?
Typically this happens when one of the ABS sensors is defective. In most cases, the BAS/ASR light come on as soon as you go over five mph.
Check the rear brake lights. Do they work properly? Does the third brake light work? It is not uncommon for a short to develop in the brake light circuit and cause such problems. If the rear brake lights don’t work, unplug them and check for corrosion. 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 you we have seen wires inside the headlight & tail light fried and cause shorts and malfunctions.
We hope that one of the tips in this article will fix your BAS/ASR light problem. Make sure to check the brake light switch, car battery, and the ABS wheel sensors. If you are still having BAS/ASR light problem, it may be time to have an auto mechanic or a Mercedes-Benz dealer in your area perform a diagnostic. 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 as what is the cause of BAS/ASR lights staying on. Other possible problems that can trigger the BAS/ASR light are a defective SAM module, bad ECU or ABS module.