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Fuses and Current Protection

by Moderator

All vehicles include current protection to limit the damage should something short out or draw more power than the wiring can handle. The objective is to disconnect a circuit that exceeds the design limits.  Tesla’s older vehicles use multiple fuses, similar to ICE vehicles.  With the release of the Model 3, Tesla switched to electronic fuses that eliminate the need for physical fuses and Tesla uses this advanced technique today in all its new vehicles.  (Feb-2023)

If you are looking for locations to obtain power for an accessory, check out our companion article:  Accessory Power Guide

Model 3/Y and Palladium S/X •  Model X (2015-2020) • Model S Refreshed (2016-2020) • Original Model S (2012-2016) • Notes

Model 3/Y and Palladium S/X

All Model 3 and Model Y vehicles use advanced current protection, as do the Model S and Model X manufactured after February 2021 (LR/Plaid).

Electronic Fuses

Electronic low-voltage fuses are a major advancement in vehicle protection. This system uses current sensors to detect an overcurrent condition, and under such conditions, electronically removes power from the circuit.  As far as we know, Tesla is the only vehicle manufacturer using this system.  Benefits include:

  • Automatic reconnection when the fault is fixed
  • Elimination of relays
  • Improved reliability
  • Faster disconnection on overload
  • Less wiring
  • Logging of intermittent issues
  • Lower weight
  • No fuse or relay replacements ever needed
  • Precise current limit controls
  • Reconfigurable limits in software
  • Reduced physical space needs
  • Software alert to the exact circuit fault

An electronic fuse design may also save costs when you add up all the expenses associated with a conventional fuse system.  This includes the primary fuses, secondary fuses, relays, fuse housings, lids, brackets, extra wiring, and labor to install and test.

Electronic Fuse Reset

It’s been reported that some eFuse items will automatically reset if the overload is gone, such as the 12v accessory power socket. Waiting 90 minutes or more should restore power.  Other eFuse functions may not reset so easily.

For example, we were doing some testing with always-on power from the drive control buttons on a 2022 Model S (the hidden drive buttons below the dual wireless phone chargers). With it powering a 400 mA dashcam, it worked fine.  We tried to add a larger 1.5 amp load for another accessory, or about 2 amps total, and it immediately “blew”.  At this point the message appeared:

center console warning

We removed all of our loads, but after 24 hours it did not clear. We also tried a hard reset and Powering down the car, but neither of these cleared the fault and restored power to this circuit. It was not a critical area, and I could otherwise use the car normally. After a software update about 10 days later, the eFuse reset.  We don’t know if all eFuses reset after a software update, so a service appointment may be necessary. To be fair, these are not areas that Tesla recommends attaching accessories.

PCS Fuses

There are a few physical fuses used in the Power Conversion System (PCS).  Depending on the PCS version, you’ll find from 9 to 11 fuses inside this module.  PCS image below is courtesy of Ingineerix with minor Photoshop work by us.

PCS

Tesla is using Littlefuse HEV 40A, 425V fuses that are soldered onto the PCB and are clearly not user-replaceable.

40 amp fuse

Pyro HV Fuse

Tesla uses a pyrotechnic fuse to disconnect the high-voltage pack in the event of a major overcurrent event.  It provides the ability to allow high peak currents needed under maximum acceleration while still providing the required overload protection. The black pyro fuse is used in the Model 3 and Model Y.

pyro fuse

The Model S and Model X use an alternate design to handle larger peak currents. The Pyro fuse assembly includes a current shunt, current sensing electronics, two small non-rechargeable long-life lithium batteries, and two 100 amp fuses in parallel.  If the electronics sense a major overcurrent event, such as a short in the motor inverter/motor assembly,  it blows the pyro fuse.  That causes all the current to pass through the two fuses which immediately blow. At this point, the HV is completely disconnected from the rest of the vehicle.  There are no CAN bus or 12v power connections to this module, as it is completely self-contained.

pyro fuse sx

Inverter Fuses

The inverters on the Model S/X, and possibly the newest 3/Y, use a clever combination of two fuses and a pyrotechnic device to protect the inverter. Should a short occur inside the motor winding, or the  HV wiring, the overcurrent is detected by electronics, and the pyrotechnic device is then activated.  This sheers off part of the two power lugs that feed the motor.  The high current also causes two connected fuses to blow.  Munro associates has an excellent Motor teardown video showing the system in action. The inverter provides 3 phase power to the motor, so two of the three connections must be disconnected in the event of a short.

HV Battery Pack Fuses

Inside the battery pack, are three additional fuses for external, non-motor high voltage connections.  These fuses are SIBA RS309-MF rated at 63 A at 700V.

Fuse 63a

Model X (2015-2020)

This fuse information is for the Model X manufactured through 31-Dec-2020. Frunk fuses are located in the frunk area, behind the center black cover plastic panel. The left side of the center console is removed to access the Cabin fusebox and the right side is removed to access the Aux fusebox.

Model X fusebox locator

Model S Refreshed (2016-2020)

This fuse information is for the refreshed Model S manufactured from 1-Jun-2016 through 31-Dec-2020. Frunk fuses are located in the frunk area, behind the center black cover plastic panel.  The Cabin fuses are located behind the right side sill panel near the firewall.

Original Model S (2012-2016)

This fuse information is for the original Model S manufactured from 22-June-2012 through 31-May-2016, prior to HW2 refresh. Most fuses are located in the frunk area, behind the center black cover plastic panels. The DC-DC Inverter and Front HV Junction box are located low on the firewall and are not easily accessible. Check the vehicle’s production date carefully, as we document the fuse functions when changes were made.

S original fuse locator

Notes

  • Dates of various changes are our best estimate of the vehicle’s manufacturing date and may be off slightly. Tesla shows the vehicle’s production month on the label near the B-pillar when the driver door is opened, but not the day of the month.
  • Fuses locations, functions, and amperages are for the North-American Left-Hand-Drive vehicles but should be very close to other variants.
  • Micro3 fuses are two fuses in one casing. We show the two functions separated by a slash.
  • Some fuses are for optional features. A fuse may or may not be populated when the option is not equipped on a vehicle.