Speedometer does not work?

Tiny
FRAWG85
  • MEMBER
  • 1994 GMC SIERRA
  • 5.7L
  • V8
  • 4WD
  • AUTOMATIC
  • 260,000 MILES
I have changed ignition switch (I was told they can go bad and are on the same circuit), VSS in tail shaft of transmission, VSSB (3 different tries), and have 2 different instrument clusters, I’ve run continuity test on all the wires everything checks out good I even replaced the ECM/PCM. I am at a loss what am I missing? Any help would be greatly appreciated.
Sunday, March 12th, 2023 AT 7:15 PM

5 Replies

Tiny
FRAWG85
  • MEMBER
  • 4 POSTS
Issue isn’t how fast I’m going I could care less but it keeps the transmission in 2nd gear and won’t let it shift throws it in "limp mode".
Was this
answer
helpful?
Yes
No
Monday, March 13th, 2023 AT 4:20 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 48,363 POSTS
There is a speedometer buffer module just behind the instrument cluster. Here is the location so you can change it out to fix the problem. Check out the images (below). Please let us know what happens.
Was this
answer
helpful?
Yes
No
Monday, March 13th, 2023 AT 11:40 AM
Tiny
FRAWG85
  • MEMBER
  • 4 POSTS
Yes, I’ve changed that out already with 3 different modules with the same numbers on it QDM followed by some numbers it’s about the size of a deck of cards a white plastic box.
Was this
answer
helpful?
Yes
No
Monday, March 13th, 2023 AT 11:52 AM
Tiny
FRAWG85
  • MEMBER
  • 4 POSTS
It’s behind the glove box on my truck next to the brain box.
Was this
answer
helpful?
Yes
No
Monday, March 13th, 2023 AT 11:54 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 48,363 POSTS
Okay, let's check the signal out of the tail housing, remove the connector and use a voltage meter set to AC millivolts. Then raise the rear to the truck and put it on jackstands to allow the rear wheel to spin, then have a helper put the truck in drive while the engine is idling. The voltmeter should show a reading here are two guides to help us with the test:

https://www.2carpros.com/articles/how-to-use-a-voltmeter

and

https://www.2carpros.com/articles/jack-up-and-lift-your-car-safely

Please go over these guides and report back.
Was this
answer
helpful?
Yes
No
Tuesday, March 14th, 2023 AT 9:21 AM

Please login or register to post a reply.

Sponsored links