2018 Mazda Mazda3 Powertrain & Transmission Problems

My 2018 Mazda 3 has an intermittent electrical failure on the high-speed CAN network that causes multiple safety-critical systems to fail while driving. When the fault occurs, the dash lights up with warnings for powertrain, ABS/traction, lane departure, collision-avoidance, TPMS, immobilizer, and the check-engine light. The car also hesitates or “lurches” between 15–30 mph during these events. At one point in 2024, the vehicle went into limp mode on the freeway, creating a safety hazard. These failures are intermittent but repeatable. Diagnostic scans from 2023–2025 show multiple U-codes for lost communication between control modules; two later became permanent. The issue appears unrelated to any one component and affects many systems at once. The vehicle has been to every Mazda dealership in the North Texas region (Mesquite, Freeman, Hiley, Norm Reeves, Town North). All performed only basic scans; none completed a full CAN-bus or wiring-harness diagnostic. Town North kept the vehicle for six weeks (Sept–Oct 2025), replaced a coil and spark plugs, performed a camera calibration and a TCM update, but the network failures returned within 38 miles. We sought independent inspection only after dealerships repeatedly refused diagnosis whenever the warning lights were not on at the moment of arrival. In November 2025, a technician found significant internal corrosion inside the negative battery cable; touching the cable reproduced the full failure immediately. The corrosion extends deep into the wire sheathing. This appears to be an electrical defect affecting CAN communication and power/ground integrity. When the fault occurs, multiple safety systems disable at once and the vehicle behaves unpredictably. Mazda Corporate has declined further assistance, and the defect remains unresolved. I am filing this report because this is a recurring safety issue that may affect other vehicles of the same model and year.

What component or system failed or malfunctioned, and is it available for inspection upon request? The high-pressure fuel pump failed. This component failure prevents the car from starting or staying running. The check engine code confirmed the high-pressure fuel pump failure. The failed component is currently at the Mazda dealership and is available for inspection upon request. How was your safety or the safety of others put at risk The car suddenly stalled while driving on the roadway, creating a dangerous situation. If this had happened on the freeway or in fast-moving traffic, it could have led to a serious accident. Losing power and control of the vehicle at higher speeds poses a major safety risk to both the driver and surrounding vehicles. I was fortunate that the failure occurred on a city street rather than on the freeway. Has the problem been reproduced or confirmed by a dealer or independent service center? Yes. The Mazda dealership inspected the vehicle and confirmed that the high-pressure fuel pump had failed, which was also verified by the check engine code. This failure caused the stalling and starting issues. Has the vehicle or component been inspected by the manufacturer, police, insurance representatives, or others? The vehicle was inspected by an authorized Mazda dealership, which diagnosed and confirmed the high-pressure fuel pump failure. It has not been inspected by police or insurance representatives. Were there any warning lamps, messages, or other symptoms of the problem prior to the failure, and when did they first appear? Before the final failure, the car was hesitant to start, and after it stalled, the check engine light appeared. There were no prior warning messages or signs before the car suddenly stalled while driving. Additional details: The car is only seven years old with approximately 52,000 miles, and it is concerning that such a critical component would fail this early.

I was driving on the highway in sixth gear and went to down shift to get on to the off ramp and was unable to get it out of sixth gear. I had it towed to the dealer where they were going to charge 4 grand just to tear down the transmission to tell me what might be wrong. So I towed it home and once I was able to get the transmission open, I found the roll pin that connects the shifting shaft to the shift selector plate had worked itself out. If the transmission had been in Neutral, it would have taken less than 20 minutes to fix. But, because it was stuck in gear the whole transmission had to be taken apart.

The contact owns a 2018 Mazda Mazda3. The contact stated while driving 25 MPH, the vehicle stalled inadvertently. The contact was unaware if there were any warning lights illuminated. The contact was able to veer to the side of the road; however, the vehicle failed to restart. The contact's husband added fuel to the vehicle; however, the failure persisted. The contact stated that the vehicle restarted 15 minutes later. The vehicle was taken to an unknown dealer who informed the contact that the failure could not be duplicated because there was no warning light illuminated. The vehicle was not diagnosed or repaired, and the failure persisted. The contact stated that the failure reoccurred upon shifting from reverse(R) to drive (D). The power train warning light and several unknown waring lights were illuminated. The contact was able to restart the vehicle and continued driving. The manufacturer was not notified of the failure. The failure mileage was approximately 32,000.

TL* THE CONTACT OWNS A 2018 MAZDA 3. THE CONTACT STATED THAT SHE WAS EXPERIENCING DIFFERENT ELECTRICAL FAILURES WITH THE VEHICLE. THE CONTACT STATED THAT THE PASSENGER SIDE SEAT BELT WARNING CHIME SOUNDED WHEN THE SEAT WAS UNOCCUPIED. THE CONTACT HAD TO BUCKLE THE SEAT BEAT TO STOP THE WARNING SOUND. IN ADDITION, BOTH PASSENGER SIDE WINDOWS FAILED TO ROLL UP AFTER BEING DOWN. ALSO, WHILE DRIVING 40 MPH, THE TRANSMISSION FAILED TO RESPOND WITHOUT WARNING WHILE DEPRESSING THE ACCELERATOR PEDAL. THE CONTACT HAD TO SHIFT THE VEHICLE FROM SECOND INTO FIRST GEAR IN ORDER FOR IT TO RESUME NORMAL OPERATION. THE CONTACT TOOK THE VEHICLE TO ODGES MAZDA AT THE AVENUES (10681 PHILIPS HWY, JACKSONVILLE, FL 32256, (904) 562-1600) WHERE A DIAGNOSTIC TEST WAS PERFORMED, BUT NO FAILURE WAS FOUND. THE FAILURE CONTINUED AND THE VEHICLE WAS NOT REPAIRED. THE MANUFACTURER WAS NOT NOTIFIED OF THE FAILURE. THE FAILURE MILEAGE WAS 18.