Speedometer is way off and transmission not shifting good?

Tiny
ROMMEL1961
  • MEMBER
  • 1998 CHEVROLET CHEYENNE
  • 4.3L
  • V6
  • 2WD
  • AUTOMATIC
  • 90,000 MILES
Speedometer was acting crazy jumping around. Transmission wasn't shifting smoothly. I replaced the vehicle speed sensor. The speedometer is smooth, not jumping around. But it is way off. It pegs out over 100 mph and Transmission still isn't shifting right. I heard that if I unplugged the VSS buffer, it may solve it. However, I can't find that buffer. Can you help?
Saturday, July 19th, 2025 AT 6:25 PM

4 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,149 POSTS
Yep, it sounds like the buffer is going out. Here is a video to help you:

https://www.youtube.com/watch?v=-NHZZGv4sxY

Let us know how it goes.
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Sunday, July 20th, 2025 AT 11:27 AM
Tiny
ROMMEL1961
  • MEMBER
  • 3 POSTS
Thanks. I'll see if it's behind the glove box like in the video and will let you know.
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Sunday, July 20th, 2025 AT 1:18 PM
Tiny
ROMMEL1961
  • MEMBER
  • 3 POSTS
It's not behind the glove box on this model. Can you advise where it's located on 1998 chevy c1500 4.3 vortec Cheyenne?
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Monday, July 21st, 2025 AT 8:41 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,149 POSTS
Okay, I did some checking, and they don't say where it is, I would assume it will be near the instrument cluster. Do you have a replacement part? Here is the VSSA in the wiring diagrams so it does have one. Check out the images (below).
Image (Click to make bigger)
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Monday, July 21st, 2025 AT 10:41 AM

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