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2021 CT5 - When to change transmission fluid? Rough shifts

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Chris P. · rep 0 · May 22, 4:00 AM · 1 replies · solved · Question

Vehicle: 2021 Cadillac CT5 Premium Luxury

My 2021 Cadillac CT5 Premium Luxury, with about 65,000 miles, has started feeling a bit off. The shifts aren't as smooth as they used to be, especially when downshifting. I'm wondering if it's time for a transmission fluid change.

The owner's manual mentions "inspect" but doesn't give a clear interval for changing the fluid. I drive a mix of city and highway, but sometimes I'm in heavy stop-and-go traffic, which I know can be hard on components.

Is this something I can do myself, or should I take it to a dealer? What kind of fluid does it even take? Any advice would be great, I want to keep this car running smoothly.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:00 AM

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It's a common misconception that modern transmissions are "sealed for life." While GM often specifies inspection rather than a strict change interval for your 2021 CT5's 10-speed automatic, severe driving conditions (heavy towing, frequent stop-and-go, mountainous terrain, or performance driving) warrant more frequent service.

Here's what to consider:

  1. Fluid Type: Your CT5 requires DEXRON ULV (Ultra Low Viscosity) automatic transmission fluid. Using the wrong fluid can cause serious damage.
  2. Inspection: At 45,000 miles, and every 15,000 miles thereafter, the fluid level and condition should be inspected. Look for dark, burnt-smelling fluid, which indicates it's breaking down.
  3. Service Interval: For severe duty, a transmission fluid and filter change is often recommended between 60,000 to 90,000 miles. Given your mileage and symptoms, it's a good time to consider it.

Causes of Rough Shifts:

  • Degraded transmission fluid (loss of lubricating properties).
  • Clogged transmission filter.
  • Low fluid level.
  • Internal transmission wear or solenoid issues.

When to See a Shop:

  • While a drain-and-fill can be a DIY task, a full fluid exchange (flush) requires specialized equipment to ensure all old fluid is removed and the system is properly refilled and bled. This is best left to a professional.
  • If a fluid change doesn't resolve the rough shifting, or if you notice any new noises or warning lights, have a qualified technician diagnose the transmission immediately. Ignoring these symptoms can lead to costly repairs.
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