Unfortunately, you or a loved one got in an accident. Even though the vehicle may seem to have gotten very little damage, there is a high chance that the car won't start even after a small collision. 

In this guide, we go over common reasons why your car won't start after an accident. It is important to realize that vehicle manufacturers implement various methods to prevent engine start after an accident. 

blow fusesWhen 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 caused by an electrical short or fuel leak.

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.

Warning!

  • Do not operate the vehicle without properly servicing the airbag system and performing a vehicle inspection.
  • If your SRS light is still on after you start the car, the airbags are inoperable. Your airbags will not deploy or protect in case of another accident.

Symptoms

  • 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

Causes

  • 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

What to do if a 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.

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).

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.

check fuses if mercedes doesn't start

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 the Mercedes prefuse box takes less than one hour.

Battery Safety Terminal

car battery safety terminal blown on a bmw

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 Engine Start

Mercedes-Benz cars are programmed to disable 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 

What we used: Autel MaxiDAS (Model 808 or newer)

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.

Instructions

  1. Connect the scanner to OBD II Port under the dashboard.
  2. Turn on ignition.
  3. Select your Mercedes-Benz model (by chassis) or allow the scanner to read VIN automatically.
  4. Select Control Unit from the main Menumercedes control unit
  5. Select Driveenable mercedes drive
  6. Select Motor Electronics.motor electronicsYou will get a warning stating: A crash event has appeared. The engine start is blocked because of crash event. Starter does not run.mercedes engine start disabled
  7. Next, you will see a question: Would you like to unlock the control module? mercedes enable start
  8. Select yesenable mercedes start after crash
  9. On the next screen, you will notice Disabling of engine start by crash event is Active.mercedes engine start enabled
  10. Press F1 Start the power disable. This will change the value to Not Active

Instructions for other scanners

  1. Connect your professional scanner to the OBD-II port under the dashboard.
  2. Turn on the ignition.
  3. Select your vehicle model.
  4. Go to Drive then Motor Electronics.
  5. Select Adaptations
  6. 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 the 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.

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 the connection from starter to the 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 an 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).