In this guide, you will find instructions on how to troubleshoot a car that won't start after an accident. Even when you replace the airbags, seatbelts, SRS module, pre-tensioners, you may find that your car won't start after a crash (or hitting a deer). Vehicle manufacturers implement various methods to prevent fires in case of an accident.
When you get involved in a car accident, the first thing that happens is the airbags deploy. But that's not all. Critical systems such as starter or fuel pump are often disconnected. These systems are disabled to prevent a fire in case of an electrical short or fuel leak. Many vehicles including Mercedes, BMW, Audi, VW, Honda, Acura, Lexus, Ford, GM, Dodge, Chryslers will either blow a fuse or the Engine Control Unit may be programmed to cut off fuel or disable engine start. In this do-it-yourself troubleshooting guide, we will look at a few items that you should check if your car won't start after an accident.
- Car engine won't crank
- Ignition turns on but nothing happens
- Ignition may not turn on at all
- Multiple warning lights on the instrument cluster
- SRS malfunction light on
- EBS malfunction warning on
- Fault code No CAN message - Engine Control Module
- All lights come on, but nothing happens when you turn key or press START
- Pre-fuse block
- Blown pre-fuse - Typically next to the battery. Will blow during airbag deployment.
- Blown pyro fuse - Mounted on the positive battery terminal
- Safety Interlock - Engine start disabled in Motor Electronics
- Power circuit open
- Antitheft system was activated
Troubleshooting Car won't start after crash
Here we troubleshoot a Mercedes-Benz that won't start after an accident but the same principles can be applied to other makes. Many cars makes automatically disconnect the battery when the airbags blow, for example, BMW vehicles. The PYRO fuse on the positive battery terminal would blow if the airbags deploy or your car determines that you are involved in an accident. On 2015 and newer Mercedes-Benz cars engine start is disabled via the control module and will need to be reset with a professional scanner.
Check Prefuse Box
One or more fuses in the pre-fuse box could blow. If a fuse blows, the power to critical systems including the starter or fuel pump will be cut off.
In this Mercedes-Benz C-Class, the pre-fuse box is located next to the battery. You can remove the prefuse box and check the fuses. Use a digital multimeter to check the continuity of all the fuses on the prefuse box. Checking Mercedes prefuse box takes less than one hour. In some cases, the prefuse box may be incorrect be called the SAM module which is incorrect.
Battery Safety Terminal
On the battery positive terminal, you may have a PYRO fuse which will disconnect the positive in case of an accident. If your car is equipped with Battery Safety Terminal, replace it after an accident.
Enable Start of Engine After Crash
Mercedes-Benz cars are programmed to not start after an accident. Even if you replace all the deployed airbags, the car still won't start. To enable the car to start, you will need to use a professional scanner to enable engine start after an accident. Generic OBD-2 scanners, will not be able to perform this step.
Enable Engine Start on a Mercedes-Benz
On newer vehicles engine start may be disabled by the Engine Control Unit (ECU) after a crash event. In the following video, we demonstrate how to enable Mercedes-Benz engine start on a 2017 Mercedes-Benz C-Class. Engine start disable via ECU affects 2015 Mercedes models and newer including C, S, E, CLS, CLA, ML, GLK, R, SL, SLK but it may also affect other car makes.
- Connect scanner to OBD II Port under the dashboard.
- Turn on ignition.
- Select your Mercedes-Benz model (by chassis) or allow the scanner to read VIN automatically.
- Select Control Unit from the main Menu
- Select Drive
- Select Motor Electronics.You will get a warning stating: A crash event has appeared. The engine start is blocked because of crash event. Starter does not run.
- Next, you will see a question: Would you like to unlock the control module?
- Select yes
- On the next screen, you will notice Disabling of engine start by crash event is Active.
- Press F1 Start the power disable. This will change the value to Not Active
Instructions for other scanners
- Connect your professional scanner to the OBD-II port under the dashboard.
- Turn on the ignition.
- Select your vehicle model.
- Go to Drive then Motor Electronics.
- Select Adaptations
- Select Enable start of the engine after crash reset.
If you do not find Enable Engine Start after the crash in the Engine Module check for this option under the Airbag / SRS module.
Run Drive Authorization
If you are troubleshooting a Mercedes-Benz and have access to a Mercedes-Benz Star Diagnostic scanner, connect it to your vehicle and run Driver Authorization test under the EIS module.
Fuel Cut Off
To prevent the vehicle from starting older Mercedes-Benz cars used inertia switch which would cut power to the fuel pump. If you have a 2000 and older Mercedes-Benz check the operation of Electric Fuel Pump Inertia Switch. If your Mercedes cranks but won't start, the problem could potentially be fuel related.
My car won't start, What's next?
Here are a few things you should check if you can't get your Mercedes-Benz to start after an accident.
- Check battery - If you hear a click when you turn the key or the lights dim, there is a very good chance that the battery is partially discharged. Charge the battery or jump start your Mercedes-Benz via the jump start terminals under the hood.
- Check connection from starter to pre-fuse box.
- Check Drive Authorization with a professional scanner, Perform a full system scan.
- Check starter - Have a friend turn the key to the start position. At the same time check voltage at the solenoid on the starter. The solenoid wire should get 12 volts only when you try to crank the engine. The larger red wire should have 12 volts constantly with the ignition on.
- Check all fuses - including fuel pump, starter, and anti-theft system.
- Make sure vehicle is in Park or Neutral - Older Mercedes-Benz used a link to shift gears (PRND) The link could bend during an accident and the car will go into the park even though the gears on the instrument cluster show as Park (P) or Neutral (N).
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