Car Won’t Start After an Accident

A common cause for a car failing to start after a minor accident is the tripping of an inertial switch. This switch, designed to protect the vehicle from potential fires, cuts power to the fuel pump in the event of an impact. As a result, the engine cannot start due to a lack of fuel supply. To diagnose and fix this issue, it’s best to consult a qualified mechanic who can check the inertial switch and repair or replace any damaged components.

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Most cars won’t start after an accident. Even though the vehicle may have gotten very little damage, there is a high chance that the car won’t start even after a minor car 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.

When you get involved in a car accident, the first thing that happens is the airbags deployed. But that’s not all.

Critical systems such as the 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, and 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.
• The airbags are inoperable if your SRS light is still on after you start the car. Your airbags will not deploy or protect in case of another accident.

Symptoms

The most common symptom is that the engine will not crank after an accident, even if you try to jump-start it.

• 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 the key or press START.

Causes

A car may not start after an accident for several reasons ranging from a blown pre-fuse (safety terminal) at the battery negative or positive post to the engine start being disabled by the vehicle in the Motor Electronics control unit. Here are some common causes why a car may not start after an accident:

1. Damage to the engine: The accident’s impact can cause bent or broken parts, such as the crankshaft or starter motor, which can prevent the engine from turning over.
2. Electrical system damage: The electrical system may have sustained damage, such as to the battery, alternator, or wiring, which can prevent the car from starting.
3. Tripped inertial switch: A switch that cuts power to the vehicle’s fuel pump after an accident.
4. Airbag deployment: Airbag deployment causes a surge in the electrical system that may damage the battery, alternator, or other electrical components.
5. Fuel system damage: Accidents may cause damage to the fuel tank or lines, preventing the engine from receiving fuel.
6. Transmission damage: An accident can cause damage to the transmission, which can prevent the car from moving or starting. Also, the shifter may have been damaged, and the car does not recognize the shifter is in the park position, which prevents the engine from starting.
7. Control module damage: Accidents can cause damage to the control module, which controls the function of the engine, transmission, and other systems.

It’s important to have the vehicle assessed by a qualified mechanic to determine the exact cause of the problem and make the necessary repairs.

What to do if a car won’t start after crash

Even if you try to jump-start the car or replace the blown airbags, seatbelts, SRS module, and pre-tensioners, you may find that your car won’t start after a crash (or hitting a deer).

Many cars, such as BMW, automatically disconnect the battery when the airbags blow. The PYRO fuse on the positive battery terminal is designed to blow if the airbags deploy or your car determines that you are involved in an accident.

In 2015 and newer Mercedes-Benz cars, engine start is disabled by the engine control module (ECU) and will need to reset with a scanner.

Check Fuse 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.

The pre-fuse box is next to the battery in this Mercedes-Benz C-Class. You can remove the Fuse box and check the fuses. Use a digital multimeter to check the continuity of all the fuses on the Fuse box. Checking the Mercedes pre-fuse box takes less than one hour.

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 Engine Start

Mercedes-Benz cars are programmed to disable start after an accident. Even if you replace all the deployed airbags, the car won’t start. To enable the car to start, you will need to use a professional scanner to enable the engine to start after an accident. Generic OBD-2 scanners will not be able to perform this step.

Enable Engine Start

On newer vehicles, engine start may be disabled by the Engine Control Unit (ECU) after a crash event. The following video demonstrates how to enable the Mercedes-Benz engine to 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, and SLK, but it may also affect other car makes.

Instructions

1. Connect the scanner to the OBD II port under the dashboard.
2. Turn on the ignition.
3. Select your Mercedes-Benz model (by chassis) or allow the scanner to read VIN automatically.
4. Select Control Unit from the Main Menu
5. Select Drive
6. Select Motor Electronics. You will get a warning stating: A crash event has appeared. The engine start is blocked because of a crash event. The starter does not run.
7. Next, you will see a question: Would you like to unlock the control module?
8. Select yes
9. On the next screen, you will notice the Disabling engine start by a crash event is Active.
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 the start of the engine after the 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, if not,  connect it to your vehicle and run the Driver Authorization test under the EIS module.

Fuel Cut Off

Older Mercedes-Benz cars used inertia switches to prevent the vehicle from starting, which would cut power to the fuel pump. If you have a 2000 and older Mercedes-Benz, check the operation of the Electric Fuel Pump Inertia Switch. The problem could be fuel-related if your Mercedes cranks but won’t start.

Why won’t my car start after the airbags are deployed?

After the airbags deploy, it is possible that your car will not start due to damage sustained to the electrical system. The deployment of the airbags requires a large amount of electrical power, which can cause a surge in the system. This surge can damage the battery, alternator, or other electrical components, preventing the car from starting.

Additionally, the impact of the airbag deployment can cause damage to the engine or other mechanical parts. To determine the cause of the problem and make repairs, it is necessary to have the car assessed by a qualified mechanic.

Troubleshooting

As a mechanic, you can troubleshoot a car that won’t start after an accident by checking the battery connections and charging system to ensure they are in good working order. Then, check the starter motor, crankshaft, and other mechanical parts for damage and ensure they are functioning properly by running a full system scan. Next, you can check the fuel system for leaks or blockages and inspect the airbags deployment sensor for damage. Additionally, you should check the transmission, control module, and all electrical connections for damage.

If you didn’t get your Mercedes-Benz to start after an accident, you should check a few things.

• Check battery – If you hear a click when you turn the key or the lights dim, there is a 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 the 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 the 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 the fuel pump, starter, and an anti-theft system.
• Ensure the 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).

Finally, you can use a diagnostic scanner to check for any error codes indicating a specific issue with the car’s systems. It is always important to thoroughly check all the systems and components to determine the root cause of the problem and make the necessary repairs.

Frequently Asked Questions

We hope you find the Car Won’t Start After an Accident guide helpful. Check these troubleshooting and repair guides for more help on your vehicle.