MB Medic Mercedes-Benz Repair Guides, Service, How To DIY
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In this guide (7 sections)
Is the SRS or airbag warning light on in your Mercedes-Benz instrument cluster? Are you getting the warning message: Restraint System Defect! SRS Visit Workshop! Low battery voltage is the most common trigger by far, and the light stays on even after a new battery goes in. A fault in the SOS TeleAid system can set it too. Keep on reading to understand how to troubleshoot and reset the SRS light.
How to Reset the Mercedes SRS Light with the UCAN-II Pro
Use the UCAN-II Pro to read SRS fault codes and clear stored codes after the underlying problem has been repaired. A current fault must be repaired before the code will stay cleared. Stored codes can usually be erased after the fault is no longer present. Codes showing as CURRENT mean you must fix the problem before clearing the code.
- Connect the scanner to the OBD-II port under the driver’s dashboard.
- Turn on the scanner.
- Select Diagnostics
- Select AutoScan VIN or manually select the vehicle model.
- Select Control Units
- Select Body
- Select Airbag or SRS (Supplemental Control System)
- Select Read Codes. Make sure all your codes are STORED in status. Any codes with CURRENT status need to be fixed to change to STORED.
- Select ERASE at the bottom of the screen.
Note that if the vehicle has been in a crash and has deployed an airbag, it may need the module replaced. After an airbag deployment, the deployed airbags and activated seat belt tensioners must be replaced. Inspect the sensors, wiring, and connectors. The SRS control module may require replacement or model-specific programming according to Mercedes service information.
What Does the SRS Light Mean?
SRS stands for Supplemental Restraint System. If this warning light stays on in your Mercedes-Benz, that means that there is a problem with the airbags or the components that are part of the SRS system. It is very unlikely that your airbags will deploy randomly, but the concern is that they may not deploy at all in the case of an accident. The vehicle may still operate, but the restraint system may not provide full protection. Diagnose the warning immediately and follow the model’s owner’s manual.
Under normal operation, when you first turn the ignition and start the car, the light stays on for about 5 seconds and then turns off. If the SRS light stays on constantly or you get a “Restraint System Defective, Visit Workshop” warning, or airbag light, you know you have a problem. A light that flashes rather than staying on steady is a separate symptom with its own causes; see Mercedes-Benz SRS airbag light flashing.
SRS Warning System
The SRS system checks the operation of several components in your car, such as:
- Airbags
- Airbag control unit
- Crash sensors
- Emergency Tensioning Devices
- Belt force limiters
- Child occupancy sensor in the front passenger seat.
These systems and other sensor data are checked when the driver turns on the ignition. If all these systems check out okay, the SRS light goes out. The SRS components are also checked frequently when the car is running. If a malfunction is detected, the SRS warning lamp or error message is displayed in the instrument cluster.
Why the SRS light will not clear on its own
The SRS light does not clear itself. Even after you fix the cause, it stays on until a scanner clears the stored code. This is why a dying battery leaves the light on long after you fit a new one.
The YOUCANIC UCAN-II Pro reads the airbag control unit along with every other module on the car, so the same tool handles SRS, ABS, ESP and transmission faults.
Compared to Xentry
Both read and clear SRS codes, and both show you the affected circuit. Xentry’s exclusive function is online VIN coding, which matters when fitting a brand new restraint module and not when diagnosing a seat occupancy sensor or a clock spring.
Common causes of an SRS or airbag warning
Low battery voltage
The most common trigger by far. A dying battery or charging fault sets the light, and it stays on after the new battery goes in. Our Mercedes battery replacement guide covers the battery sensor, whether the new battery needs registering, and the sync procedures.
Seat occupancy sensor
In the front passenger seat. A known wear item and a frequent cause on older cars. See child seat occupancy recognition sensor problems and solutions.
Clock spring
The coiled contact behind the steering wheel. Often shows up alongside non-working horn or steering wheel buttons.
Seat belt latch or tensioner
The buckle switch or the emergency tensioning device circuit.
Wiring under the seats or in the doors
Connectors get kicked, corroded or pinched. Check these before condemning a module.
Crash or impact sensor
A damaged sensor, connector or wiring run, often after minor front end work.
After an accident: crash data and the SRS module
If an airbag has deployed, the restraint control module stores crash data and locks. Clearing codes will not reset it. The deployed airbags and activated seat belt tensioners must be replaced, and the module needs either replacement or a crash data reset.
- Airbags and emergency tensioning devices work once. Never reuse a deployed unit.
- Before disconnecting any SRS component, switch off the ignition, disconnect the battery per the model procedure, and wait the specified discharge time.
- Never probe an airbag igniter circuit with a test light or a standard ohmmeter.
- Do not fit seat covers unless Mercedes-Benz approved them. They interfere with seat mounted airbags.
- Airbags contain perchlorate and release a fine powder on deployment. Avoid breathing it in.
- Work carefully in the doors and under the seats. Sensors and wiring live there.
Read the SRS code before you replace anything
Battery, clock spring and seat sensor all show the same light. The code names the circuit.
Related guides
- SOS TeleAid malfunction warning
- Mercedes seat belt locked after an accident
- Mercedes-Benz fault code list
Before you buy parts, scan every control module, not just the engine. It shows the root fault behind the warning lights and tells you whether the problem is still active. See how to do a full health check.
