Today, let's talk about the "Pyrofuse." What exactly is it? Why isn't it found in every car? Which vehicles typically have it? How can it help in second-hand car appraisals? Let's explore these questions in today's article.

1. What is a Pyrofuse and what does it do?

A Pyrofuse, also known as a Pyroswitch or Pyrotechnical Safety Switch (PSS).

So, what exactly does this device do? The primary function of a Pyrofuse is to act as a switch. In the event of a collision, short circuit, or other safety faults, the Pyrofuse can cut off the power in a very short time, reducing the probability of danger.

Currently, Pyrofuses are used in battery systems, which reminds me of BMW's SBT. BMW's Safety Battery Terminal activates upon detecting a collision signal, using an explosive charge to disconnect the battery terminal, thus cutting off the power supply close to the battery to prevent short circuits and fires. However, not all vehicles are equipped with this device. It is mainly found in high-end vehicles, sports cars, and electric vehicles, such as BMW, Porsche, and Tesla. Pyrofuses are typically installed near the battery or high-voltage battery, but their locations can vary, requiring special attention during vehicle appraisals.

2. Structure and Location of the Pyrofuse in the Porsche 911

The design of the Pyrofuse in the 2022 Porsche 911 is quite remarkable. It is located under the center console, to the right of the accelerator pedal.

This device in the image is the Pyrofuse of the Porsche 911. To replace it, the entire center console must be removed, which can be quite costly. However, this design can actually aid in quickly appraising a Porsche 911. If the vehicle has been in a collision, whether this part has been replaced is a key indicator.

The design of the Porsche 911's Pyrofuse is relatively simple. The image shows its internal structure, although the part displayed is damaged, showing the internal metal strip has broken. Tesla’s Pyrofuse design is much more complex, which we will examine next.

3. Structure and Location of the Pyrofuse in Tesla Vehicles

Here is the Pyrofuse in a Tesla. Its appearance is similar to those in fuel vehicles, but the internal structure differs.

Upon opening the cover of the Tesla Pyrofuse, you'll find a piston with an explosive charge. When the ECU sends a signal, the charge explodes, pushing the piston downward.

Below the piston is an aluminum strip, with its thinnest point in the middle. As the piston moves down, it cuts through this thin point, disconnecting the entire battery system and preventing short circuits and fires.

Below the aluminum strip are U-shaped metal pieces. During the explosion, these structures produce smoke and sparks, serving to extinguish the arc.

How to Replace the Pyrofuse in a Tesla?

First, let's familiarize ourselves with Tesla's high-voltage components: 1 is the high-voltage cable, marked by an orange harness on the vehicle, 2 is the heat pump assembly, 3 is the front motor, 4 is the high-voltage battery, 5 is the high-voltage cable, 6 is the inspection cover of the high-voltage component (distribution box), 7 is the rear motor, 8 is the high-voltage busbar, and 9 is the charging port.

1.To replace the Pyrofuse, disconnect the battery

Tesla Model 3 has two types of batteries: the older 12V battery and the newer 16V lithium battery, both installed in the front trunk. The image shows the 16V lithium battery. To disconnect it, use a flathead screwdriver to lift the green clip.

Pull the black plastic frame to the right, then pull out the harness by hand. However, disconnecting the battery alone is not enough; the connector between the high-voltage battery and the battery must also be disconnected. This connector is located on the inspection cover of the high-voltage component (distribution box).

When appraising a Tesla Model 3, it is crucial to check the inspection cover of the high-voltage component (distribution box), located under the rear seat.

The rear seat of the Tesla Model 3 is fixed with white plastic clips on both sides. Unlike typical rear seats, it does not simply lift up for removal.

To remove it, first locate the clips, push the black metal piece to the right, and then lift to detach the rear seat.

Once the rear seat is removed, there is a harness connector on the passenger side. This needs to be disconnected to fully power off the battery.

2.Replacing the Pyrofuse

After disconnecting the power, you can proceed to replace the Pyrofuse. Open the inspection cover of the high-voltage component (distribution box), located inside.

Lift the rear seat, then remove the longitudinal black fixing bracket and the aluminum cover underneath. There are various bolts securing it. Check for any signs of tampering during the appraisal.

Once the cover is removed, you can see the internal structure. The Pyrofuse is located on the driver’s side, within the pink dotted box in the image.

Remove the bolts securing the Pyrofuse on both sides to replace it. To determine if the Pyrofuse in a Tesla Model 3/Y has been replaced, check the following:

(1).Any signs of tampering on the bolts of the high-voltage component (distribution box) inspection cover.

(2).Any signs of tampering on the bolts securing the Pyrofuse.

(3).Whether the production date on the Pyrofuse matches the vehicle’s manufacturing date.

Understanding the function and role of the Pyrofuse reveals that it only disconnects during significant collisions, preventing the vehicle from starting. This is not a minor collision but one likely involving airbag deployment. If you cannot determine the extent of the collision during the appraisal, the Pyrofuse can be a critical clue.