By YOUCANIC on May 23, 2019
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.
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.
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 the Mercedes prefuse box takes less than one hour.
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.
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.
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 for other scanners
If you do not find Enable Engine Start after the crash in the Engine Module check for this option under the Airbag / SRS module.
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.
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.
Here are a few things you should check if you can't get your Mercedes-Benz to start after an accident.