Speedometer inaccuracies

TexasRebel · Feb 10, 2019

Picked up my 96 1500 with a 4.3 4l60e about 2 weeks ago. I have to use a GPS speedometer on my phone to get an accurate reading. At around 30mph it says I'm doing 35ish. At 65mph, it says I'm doing 75ish. At 75mph, it says I'm doing almost 90. All other gages seem to be working properly and accurately so I don't think it's a ground issue. My only clue so far is the abs light being on. I've read that a bad abs sensor can cause bad speedometer readings and also hard shifting (which the truck does).

Any help would be greatly appreciated.

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chris2323 · Sep 21, 2022

TexasRebel said:
Picked up my 96 1500 with a 4.3 4l60e about 2 weeks ago. I have to use a GPS speedometer on my phone to get an accurate reading. At around 30mph it says I'm doing 35ish. At 65mph, it says I'm doing 75ish. At 75mph, it says I'm doing almost 90. All other gages seem to be working properly and accurately so I don't think it's a ground issue. My only clue so far is the abs light being on. I've read that a bad abs sensor can cause bad speedometer readings and also hard shifting (which the truck does).

Any help would be greatly appreciated.

Sent from my SM-N950U using Tapatalk

Did you ever figure out what was causing this? Im having the same problem as well except i dont have an abs light on

TexasRebel · Sep 23, 2022

chris2323 said:
Did you ever figure out what was causing this? Im having the same problem as well except i dont have an abs light on

No resolution found yet man. Pretty much just decided to deal with it until I get around to doing the 5.3 swap since I'll be swapping the cluster at the same time. I've talked to a couple people that think it may be the motor that controls the gauge. You can buy them online and swap them out, thought it is a little tedious. I've also considered sending the cluster to a repair shop to have it rebuilt but can't afford to lose all of my gauges in my only running vehicle until I get it back.

chris2323 · Sep 23, 2022

I was thinking i had a bad cluster/stepper motor as well. Both my rpm and mph are off. I tried 2 different instrument clusters from a salvage yard, and they both had the same error. Either i just got bad parts, or there is something else going on. I know my pcm is reporting the correct mph/rpm because i can see it during a scan. Good luck with the 5.3!

618 Syndicate · Sep 23, 2022

Smaller tires will show a higher speed on the speedo than you're going.

TexasRebel · Sep 25, 2022

618 Syndicate said:
Smaller tires will show a higher speed on the speedo than you're going.

My tires are 1.5" shorter than factory but that isn't my issue. If that were the case, the speed would be off fairly consistently across the range where as mine is erratic and way off at any speed.

618 Syndicate · Sep 25, 2022

TexasRebel said:
My tires are 1.5" shorter than factory but that isn't my issue. If that were the case, the speed would be off fairly consistently across the range where as mine is erratic and way off at any speed.

That may be one issue amongst others? Making something else worse maybe? It's about 8% variance.

Killerc998 · Sep 25, 2022

https://www.discounttire.com/learn/tire-size-calculator use this as a guide/ help explain the speed difference.

Hoplite · Sep 26, 2022

My 95 has done this for years. I bought it about 7 years ago with 90k miles. It’s always had an offset very similar to yours. However mine is a 4l80e, 373 truck on stock ish 245 tires.

Speedometer inaccuracies

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chris2323

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618 Syndicate

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618 Syndicate

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