2020 Cadillac CT6 Problems: 6 Known Issues

On the 2019-2020 Cadillac CT6, certain 2019-2020 Cadillac CT6 vehicles equipped with a 10-speed transmission can develop internal transmission damage that may cause the wheels to lock while driving.

On the 2016-2020 Cadillac CT6, on some 2016–2020 CT6 vehicles with the 3.6L LGX or 3.0L LGW engine, water-pump noise can accompany DTC P0324. GM PIP5545C directs technicians to compare pump noise and knock-retard readings with the accessory belt installed and removed. If the tests do not support the pump as the source, follow normal service diagnostics.

On the 2016-2020 Cadillac CT6, cT6 owners report the radiator cooling fans running at high speed all the time — including after shutdown — with the coolant temperature gauge reading cold, and in many cases weak heater output and the A/C refusing to engage. The root cause is a thermostat that fails stuck open. The engine never reaches its target coolant temperature in the calibrated time, so the ECM sets P0128 (coolant temperature below thermostat regulating temperature), defaults the temperature gauge to the cold end, commands the A/C off, and commands the cooling fans on as a protective default. Owners frequently mistake this for a fan relay, a fan module or a bad temperature sensor and replace those first.

On the 2020 Cadillac CT6, gM recalled 2020 Cadillac CT6 sedans fitted with dealer-installed accessory 20 x 8.5-inch wheels (RPO 5JO or SHH) under NHTSA campaign 19V731. The tire pressure monitoring sensors mounted in those accessory wheels transmit on the wrong radio frequency, so the car's TPMS receiver never hears them and the low-pressure telltale cannot illuminate when a tire goes soft. The vehicles fail to comply with FMVSS 138. Only 81 vehicles are affected, which is exactly why it is worth checking: a used 2020 CT6 wearing accessory 20s is the specific car at risk, and a driver can run a badly underinflated tire with no warning at all.

On the 2016-2020 Cadillac CT6, the CT6's rear camera mirror streams a live video feed from a roof-mounted rear camera onto the mirror glass. Owners report the feed going blank, showing a grainy, pixelated or heavily distorted picture, or losing focus so badly at night and in rain that the mirror is unusable. GM addressed the image-quality complaint in TSB 17-NA-375 for grainy, distorted or pixelated rear vision camera images on the CT6, but a share of cars have an outright module or camera failure that dealers resolved by replacing the assembly. Compounding it, using the rear washer sprays fluid onto the camera lens and smears it, and moisture accumulation defeats the lens's hydrophobic coating in wet, humid weather.

On the 2016-2020 Cadillac CT6, cT6 owners report the 12-volt battery going flat after the car sits for a few days, sometimes flat enough that the electronic shifter and door handles will not respond and the car needs a jump. GM preliminary information PIC6359A for 2016-2020 CT6 vehicles explains a cycling battery draw that technicians find when diagnosing these complaints: the keyless entry control module polls for the key fobs to support approach lighting. GM classes this as normal draw that steps down over several days, but fobs stored within about 16 feet of the car can keep triggering approach lighting and drain the battery. Other modules that fail to time out (infotainment, security) produce the same symptom, so the offending module has to be identified rather than assumed.