2018 Mazda Mazda6 Powertrain & Transmission Problems

System Failure: The Power Train (6-speed Automatic Transmission) suffered a major malfunction, documented by diagnostic codes P0731 (Gear 1 Incorrect Ratio) and P0780 (Shift Error). The vehicle is available for inspection. Safety Risk: The failure caused a sudden loss of propulsion while attempting to accelerate. This created an immediate risk of a rear-end collision and left the vehicle unresponsive in the path of oncoming traffic. The transmission's unpredictable shifting makes the vehicle unsafe to operate. Confirmation: The failure and the P0731 code were officially confirmed by Castle Mazda on March 2, 2026. The manufacturer (Mazda) has been notified but has denied a remedy, despite TSB MC-10160555-0001 addressing this specific internal defect. Warning Symptoms: There was no Check Engine Light or dashboard warning prior to or during the failure. The only warning was an extreme, abnormal mechanical grinding/clunking noise from the transmission. The lack of a malfunction indicator light (MIL) meant I had no electronic warning of a looming mechanical failure while in motion.

I recently discovered a significant oil leak near the exhaust manifold of my 2018 Mazda 6 (2.5L NA), which has resulted in visible smoke and a burning oil odor. Upon taking the vehicle to the nearest Mazda dealership for a diagnosis, the service department informed me that the vehicle has suffered a cracked cylinder head. An active oil drip is visible behind the engine near the exhaust manifold immediately upon starting the car; consequently, the engine is leaking oil directly onto the exhaust components. This condition not only renders the vehicle inoperable but also presents a significant safety and fire hazard. At the time of this writing, my vehicle has only 46,996 miles and has been meticulously maintained. This mileage is well under the 60,000-mile powertrain threshold and represents a premature failure of a major internal engine component. There are numerous reports on Mazda owner forums describing this identical issue occurring in Mazda 6, CX-5, and CX-9 models. Some owners have even reported instances of minor fires or active burning under the hood due to oil contacting hot engine components. Mazda released Technical Service Bulletin TSB #MC-10241612-0001 (SA-037-23), which includes a redesigned cylinder head for 2018–2020 Mazda 6, 2019 CX-5, and 2016–2020 CX-9 models, demonstrating Mazda’s awareness of this design flaw. While the TSB currently only specifies the 2.5L Turbo engines and not the naturally aspirated variants, there is substantial evidence that this is a widespread defect across these model years, unrelated to owner misuse or vehicle mileage. Mazda should take full responsibility by issuing a formal recall or providing an extended warranty to cover naturally aspirated engines, thereby addressing this problem and preventing further safety risks.

Was driving then car suddenly shut down and all panel lights turned on. The car would not start after an hour it started but was Perkins when driving. Mechanics were unable to diagnose the issue.

Noticed slight coolant leak, took car to mechanic, he stated cylinder head was cracked, & causing coolant to spray everywhere. Towed car to dealer. Was given repair estimate of over $11,000, for a new engine. I see a safety bulletin online for my year make & model car. This overheating can apparently cause an engine fire. So far, Mazda seems to be showing negligence & not properly addressing the issue for owners.

I took my car in for scheduled maintenance and the technicians at the Mazda dealer found out the tensioner and belt needed to be replaced, when the car is less than 36k in miles. Vehicles being repaired under warranty but a tensioner should not be going out this early in the lifespan of a 2 year old car. I have found a lot of people are complaining for the same issue. This can cause the cars to not run as there’s no notice ahead of time that the belt and tensioner are bad. I do have paper work stating tensioner problems. Vehicles should be recalled due to poor manufacturing and parts making it unsafe on the road.

The contact owns a 2018 Mazda Mazda6. The contact stated that he had experienced a transmission surged on five separate occasions since owning the vehicle. There were no warning lights illuminated. The contact had taken the vehicle to the dealer after each failure and various unknown repairs and software updates were performed on the vehicle. However, the failure persisted after each visit. The manufacturer was notified of the failure and a case was opened. The vehicle was not repaired. The failure mileage was approximately 10,000.

VEHIXLE HAS OPEN RECALL #3719F. TOOK VEHICLE IN FOR SERVICE ON JULY 15 AND ACCORDING TO NHTSA RECALL HAS EVEN OUT SINCE JUNE 27.2019. TO THIS DAY I HAVE NOT GOTTEN ANY LETTER OR ANYTHING STATING CAR HAS OPEN RECALL WHEN THE CAR CAN TURN OF RANDOMLY. WILL BE TAKING CAR IN ON 08/26/19 BUT I'M CONCERNED AS TO WHY THIS HAS NOT BEEN ADDRESSED IN ANY LETTERS OR EMAILS