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2018 Acadia Denali Transmission Hesitation and Hard Shifts - What's going on?

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Christine P. · rep 0 · May 22, 3:47 AM · 1 replies · solved · Question

Vehicle: 2018 GMC Acadia Denali

Hey everyone,

I've got a 2018 GMC Acadia Denali with about 75,000 miles on it, and lately, the transmission has been acting really strange. When I'm accelerating from a stop, there's often a noticeable hesitation before it finally engages, almost like it's slipping. It's especially bad going from 1st to 2nd gear.

Beyond the hesitation, I'm also experiencing some pretty harsh shifts, particularly when downshifting at lower speeds. It feels like a jolt sometimes. I've checked the fluid level, and it seems okay, but I'm not sure what else to look for. Is this a common issue with these 9-speed transmissions? Should I be worried about a major repair?

Any advice or similar experiences would be greatly appreciated!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 3:47 AM

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ClearTheCode admin answer:

Transmission issues like hesitation and hard shifts in your 2018 GMC Acadia Denali can be concerning, but there are several common causes and diagnostic steps to consider.

  1. Check for Diagnostic Trouble Codes (DTCs): Even if the Check Engine Light isn't on, a pending code might be present. Common transmission-related codes include P0700 (Transmission Control System Malfunction), P0716 (Input/Turbine Speed Sensor Circuit Range/Performance), or P0722 (Output Speed Sensor Circuit No Signal). A professional scan tool can read these.

  2. Software Updates: Many modern transmissions, including the 9-speed in your Acadia, rely heavily on software. GM frequently releases software updates to improve shift quality and address known issues. A dealership can check if your vehicle's Transmission Control Module (TCM) has the latest calibration.

  3. Transmission Fluid Condition: While you checked the level, the condition of the fluid is also critical. Dark, burnt-smelling fluid indicates excessive wear and heat, suggesting internal problems. Even if the level is good, old fluid can lose its lubricating properties. A fluid and filter change might be recommended, but only after proper diagnosis.

Common Causes:

  • Worn Valve Body: The valve body controls fluid flow to engage gears. Wear or sticking valves can cause erratic shifting.
  • Faulty Solenoids: Solenoids direct fluid pressure. If they fail, shifts can become harsh or delayed.
  • Torque Converter Issues: A failing torque converter can cause slipping and hesitation, especially during initial acceleration.
  • Internal Wear: Clutch packs or bands can wear out over time, leading to slipping.

When to See a Shop: It's highly recommended to have your Acadia inspected by a qualified transmission specialist or a GMC dealership as soon as possible. Continuing to drive with significant transmission issues can lead to more severe and costly damage. They can perform a comprehensive diagnostic, including:

  • Reading advanced DTCs.
  • Checking transmission fluid pressure.
  • Performing road tests with diagnostic equipment.
  • Inspecting for internal mechanical failures.

Addressing these symptoms early can prevent a complete transmission failure.

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