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 trusted mechanic to check the inertial switch and repair or replace any damaged components.

Most cars won’t start after an accident. Even though the vehicle may have sustained minimal damage, there is a high chance it won’t start. In this guide, we go over common reasons why your car won’t start after an accident. It is essential 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, may blow a fuse or have the Engine Control Unit programmed to cut off fuel or disable engine start.

Warning!

• Do not operate the vehicle without adequately 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. They will not deploy or protect you 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 include:

• The 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 bend or break 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 damage the transmission, which can prevent the car from moving or starting. Also, the shifter may have been damaged, and the car does not recognize that it 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 essential 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 a 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, the engine control module (ECU) disables engine start, which must be 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 fuse. Use a digital multimeter to check the fuse’s continuity on the fuse box. Checking the Mercedes pre-fuse box takes less than one hour.

Battery Safety Terminal

You may have a PYRO fuse on the battery-positive terminal, which will disconnect the positive in case of an accident. If your car has a 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 vehicle to start, you must use a professional scanner to allow the engine to start after an accident. Generic OBD-2 scanners will not be able to perform this step. The YOUCANIC Full System Scanner can NOT enable the vehicle after a crash at this time.

Enable Engine Start

On newer vehicles, the Engine Control Unit (ECU) may disable engine start 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 to 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 starts with an active crash event.
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,  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 or 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. Deploying 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 damage the engine or other mechanical parts. A qualified mechanic must assess the car to determine the cause of the problem and make repairs.

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 function correctly by running a full system scan. Next, you can check the fuel system for leaks or blockages and inspect the airbag deployment sensor for damage. Additionally, you should check the transmission, control module, and all electrical connections for damage.

You should check a few things if you didn’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, the battery is likely 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 starter’s solenoid. 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-Benzes used a link to shift gears (PRND). The link could bend during an accident, and the car would 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, like the YOUCANIC Full System 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. For more help with your vehicle, check these troubleshooting and repair guides.

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