2018 Tesla Model 3 electrical system problems

“While my wife was driving, the high-voltage battery failed and the car went into reduced power/limp mode. Tesla later determined that coolant had gotten into the high-voltage battery and caused it to fail. My main concern is that we had no warning that there was a coolant leak or that coolant was getting into the battery. There was no low-coolant warning or anything telling my wife that there was a serious problem developing. By the time the car started giving high-voltage and reduced-power warnings, the damage had already occurred and Tesla said the battery needed to be replaced. What concerns me even more was what happened after Tesla received the car. Tesla removed the battery and quarantined it in the parking lot. They told us in writing that it was removed because of coolant ingress as a safety precaution and that a specialized technician had to determine whether the battery was safe to discharge. During a phone call, a Tesla employee also told me they quarantined it because there was a possibility the battery could explode and they did not want anyone injured or anything damaged if that happened. That was alarming because my wife had just been driving…”

“Component/system: The front passenger Occupant Classification System (OCS) in my 2018 Tesla Model 3. The vehicle is available for inspection on request. Description of the failure: The vehicle intermittently displays "Front passenger safety restraint system fault — service required]" on the center touchscreen. The alert first appeared on or about 4 years ago and has recurred approximately ~50 times since. The failure is strongly correlated with cabin temperature. It appears after the vehicle has been parked in direct sun in warm weather, and clears on its own once the cabin cools. It has not occurred in cooler ambient conditions. Safety risk: On this vehicle the front passenger seat uses a capacitive Occupant Classification System rather than a simple occupant-detection pad. The restraint control module uses OCS output to determine both whether the passenger airbag deploys and at what force. When the system faults, I have no way to know whether the passenger airbag is suppressed, will deploy at an inappropriate force for the occupant, or will deploy at all. This directly compromises frontal crash protection for anyone in that seat. I have been avoiding seating…”

“Vehicle displayed a “Safety Restraint System Issue - Service Required” alert (fault codes RCM_a056 and RCM_a032). Tesla diagnosed an open circuit between the driver-side curtain airbag and the left airbag controller, requiring replacement of the left body harness. Tesla quoted approximately $1,800–$2,200 for the out-of-warranty repair. This is a known, recurring pattern — multiple other 2018 Tesla Model 3 owners report experiencing this identical fault at nearly the same mileage (~78,000 miles), suggesting a design or component wear issue rather than isolated damage, similar to a prior Tesla trunk-harness recall (NHTSA campaign 21V-00D) that also stemmed from a wiring/harness defect on this same vehicle. I am requesting NHTSA investigate whether this represents a safety-defect trend warranting a recall.”

“High voltage fast charge contactors experienced partial weld failure (BMS_a167_SW_FC_Partial_Weld) during routine Supercharging, causing complete HV system shutdown (hvState = HV_DOWN). Vehicle also threw BMS_a085/a086 Pack and Fast Charge Contactor Mismatch codes. Tesla service is refusing to cover repair under the 8-Year HV Battery Warranty, claiming fast charge contactors are not a warranted component despite being integrated into the HV battery assembly. Vehicle has been at Duluth, GA Tesla Service Center since approximately June 8, 2025.”

“The contact owns a 2018 Tesla Model 3. The contact stated that while opening the doors of the vehicle, the driver's side seat back unintendedly reclined and pressed down on the rear seat, causing the cushion to become deformed. The contact manually used the seat controls to return the seat to an upright position. There was no warning light illuminated. The contact stated that the failure was intermittent and only occurred while the doors were opened. A Tesla service center was contacted; however, an appointment was not scheduled for diagnostic test. The contact was provided an estimate for the repair. The vehicle was not diagnosed or repaired. The failure mileage was approximately 95,000.”

“The contact owns a 2018 Tesla Model 3. The contact stated that there was a feature in the vehicle that allowed the front driver’s seat to automatically adjust according to the saved driver's profile. The contact stated that the driver’s seat back and forth movement to adjust to each driver's profile might have caused loose wire connection, resulting in error code: RCM_a021 (Front Left Safety Restraint System Fault) being displayed. The contact stated that the error message had been displayed intermittently. Upon investigating the failure online, the contact related the failure to the seat adjustment feature. The failure was reported to the manufacturer through the Tesla App; however, the contact had not yet received a response. The vehicle was not diagnosed or repaired after the failure. The failure mileage was approximately 55,000.”