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Rough Shifting on my 2018 Sierra 1500

0

Mike T. · rep 0 · May 25, 2:36 AM · 1 replies · solved · Question

Vehicle: 2018 GMC Sierra 1500 SLT

Hey everyone,

I've been noticing some really rough shifts lately in my 2018 GMC Sierra 1500 SLT, especially when going from 1st to 2nd gear, and sometimes from 3rd to 4th. It feels like a jolt and it's getting worse. The truck has about 85,000 miles on it.

There's no check engine light on yet, but the transmission just doesn't feel right. It's almost like it's slipping sometimes before it finally engages with a thud. Has anyone else experienced this with their Sierra?

I'm worried this could be a major transmission issue. Any advice on what I should check first or if this is a common problem for this model year?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 2:36 AM

0

ClearTheCode admin answer:

Rough shifting in a GMC Sierra, especially between lower gears, can be a sign of several underlying issues. It's good you're addressing it early.

Possible Causes:

  1. Low or Contaminated Transmission Fluid: The most common cause. Low fluid levels can prevent proper hydraulic pressure, leading to harsh shifts. Contaminated fluid (burnt smell, dark color) indicates wear and tear or overheating.
  2. Transmission Solenoids: These electronic valves control fluid flow within the transmission. A faulty solenoid can cause delayed or harsh shifts. Common OBD-II codes related to solenoids include P0751, P0756, P0776, P0796.
  3. Transmission Control Module (TCM): The TCM manages the transmission's operations. A software glitch or a failing module can cause erratic shifting.
  4. Worn Clutch Packs or Bands: Internal wear within the transmission can lead to slipping and harsh engagement.

What to Check:

  1. Check Transmission Fluid Level and Condition: Park on a level surface, warm up the engine, and check the fluid using the dipstick (refer to your owner's manual for specific procedure). Note the color and smell. It should be reddish and not smell burnt.
  2. Scan for Codes: Even without a Check Engine Light, a pending or history code related to the transmission (e.g., P0700 - Transmission Control System Malfunction) might be present. A professional scan tool can reveal these.

When to See a Shop:

  • Immediately if the problem worsens, you hear grinding noises, or the transmission completely fails to engage a gear.
  • As soon as possible if the fluid is dark/burnt, or if scanning reveals active transmission-related OBD codes. A qualified mechanic can accurately diagnose the issue, whether it's a simple fluid change, solenoid replacement, or a more extensive transmission repair. Ignoring these symptoms can lead to more severe and costly damage.
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