NHTSA complaint #11660789

Owner complaint summary

About 5 weeks ago, our Navigator's transmission had a mild slip, like it was accidentally put in neutral. Since there was no visible warning sign, check engine light, or clear indicator of transmission issues, we thought it may just be a fluke. Within weeks, the transmission slipping escalated from mild to extreme, causing major safety concerns. When in drive, it would struggle to accelerate, get stuck in the wrong gear, then overcompensate, violently jerking into the correct gear 20+ seconds after it should have. A few times, we narrowly avoided getting rear-ended or rear-ending others. Lincoln service confirmed the 10-speed automatic transmission in the 2019 Navigator is problematic and will likely need a full rebuild, yet there is no transmission recall. They also stated their service department was backed up 4-5 weeks due to transmission repairs. Over the last 2 weeks, we've had a full vehicle diagnostic and repair. The mechanic replaced both leaky transmission coolant lines and completely rebuilt the transmission. He confirmed the check engine light never activated and diagnostic trouble codes never generated. That is an extreme safety problem. According to Lincoln, with leaks and transmission slipping, DTCs should be generated, and check engine lights should come on, but it didn't happen in either case. Please investigate both the transmission failures and the trouble code generation!