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2017 LaCrosse V6 - Harsh Shifting, Especially 1st to 2nd

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Chris P. · rep 0 · May 25, 2:44 AM · 1 replies · solved · Question

Vehicle: 2017 Buick LaCrosse Premium

Hello Buick forum,

I'm experiencing some concerning transmission behavior in my 2017 Buick LaCrosse, which has the 3.6L V6 engine and the 8-speed automatic. Lately, the shifts have become very harsh, especially when going from 1st to 2nd gear, and sometimes 2nd to 3rd. It feels like a jolt or a hard thump, particularly when the engine is cold, but it can happen even after it's warmed up.

There's no check engine light or transmission warning light on, which is odd. The fluid level seems fine, and it doesn't smell burnt. I'm worried this might be a sign of a bigger problem with the transmission. It has about 70,000 miles on it.

Has anyone else with a similar LaCrosse or other GM 8-speed experienced this? What was the resolution?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 2:44 AM

0

ClearTheCode admin answer:

Harsh shifting, especially from 1st to 2nd or 2nd to 3rd, on a 2017 Buick LaCrosse with the 8-speed automatic transmission (often the 8L45 or 8L90) is a known concern for some owners. Even without a check engine light, this can indicate an internal transmission issue.

Common Causes & Diagnostic Steps:

  1. Transmission Fluid Condition/Level: Although you mentioned the fluid looks fine, ensure it's checked according to the manufacturer's specific procedure (often at a certain temperature and with the engine running). Incorrect fluid type or degraded fluid can cause shifting issues.
  2. Transmission Control Module (TCM) Software: Sometimes, harsh shifts can be resolved with a software update for the TCM. GM has released various updates to improve shift quality and address specific shift complaints.
  3. Valve Body/Solenoid Issues: The valve body contains solenoids that control fluid flow to engage different gears. A sticking or failing shift solenoid (e.g., P0751, P0756 for specific solenoids) can cause harsh or delayed shifts.
  4. Torque Converter Clutch (TCC) Issues: Problems with the torque converter clutch can sometimes manifest as harsh shifts or shuddering, though it's more often associated with lock-up issues.
  5. Internal Wear/Damage: While less common at 70,000 miles without codes, internal wear on clutch packs or other components could lead to harsh engagements.

When to See a Shop:

  • Soon: It's important to address transmission issues promptly to prevent further, more expensive damage. A specialized transmission shop or a Buick dealership is recommended.
  • Professional Diagnosis: They will:
    • Scan the vehicle for any pending or historical transmission-specific diagnostic trouble codes (DTCs), even if the CEL isn't on (e.g., P0700 for general transmission malfunction, or more specific P07XX codes).
    • Check the transmission fluid condition and level accurately.
    • Check for available software updates for the TCM.
    • Perform a road test with a diagnostic scanner to monitor shift pressures and solenoid operation in real-time.
    • If necessary, perform a transmission fluid flush/change using the correct fluid type (e.g., Dexron HP).
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