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Speedometer is reading too fast?

Tiny
CHARLESTUCK
  • MEMBER
  • 1999 CHEVROLET 1500
  • 5.7L
  • 2WD
  • AUTOMATIC
  • 150,000 MILES
My speedometer reads double as I increase the speed. It starts out being about 10 - 15 MPH too fast. All of the other instruments and gauges work correctly and there are no codes.
Sunday, January 22nd, 2023 AT 3:21 PM

3 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,709 POSTS
Hi,

There are two different transmissions that were used, a 4L60 and a 4L80. There should be a tag on the side of the trans housing indicating which one you have.

These vehicles have an electronic output speed sensor. I attached a pic for both transmissions below. Check to see if there is anything loose or damaged at the connector. If it looks good, remove the sensor and inspect it for damage, dirt, or anything that prevents it from creating a proper signal.

If you look at the last pic below, it diagnoses an inoperative speedometer. It explains how to test the sensor. You may want to consider that as well.

Let me know what you find. Also, let me know if there has been any work done recently.

Take care,

joe

See pics below.
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Sunday, January 22nd, 2023 AT 8:13 PM
Tiny
CHARLESTUCK
  • MEMBER
  • 59 POSTS
I don't have any way to have the allow the wheels to roll while suspended. Are you suggesting that the speed sensor is bad? That speedometer is the only instrument that is not accurate and there is no check engine light or diagnostic code. The speedometer has been like that for about 6 years. I have been relying on my GPS, but now I want it fixed to be certain that it is recording the correct mileage.
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Tuesday, January 24th, 2023 AT 1:57 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,709 POSTS
Hi,

I understand. As far as my guess, I would think there is an issue with the vehicle's speed sensor. I would remove and inspect it at a minimum. If that isn't the issue, either we have a wiring issue or there is an issue with the cluster.

Let me know your thoughts and questions. Also, please understand that it is difficult to diagnose this without testing.

Let me know.

Joe
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Tuesday, January 24th, 2023 AT 2:13 PM

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