Speedometer not reading correctly.

[PanchohasAyukonno]

Hi there looking for some insight/guidance, first time with GM and first Yukon 2008 5.3 200k miles, I need some help my speedometer is 10mph off it reads higher than the speed im going. I would like to know where to start a sensor, abs wheel speed sensors or even looking in tune or am I over thinking it. Thank you in advance.

 

[sikhoe]

Are you running a different size tire then stock?

 

[strutaeng]

You just bought the vehicle? Do you know the history?

Agree on confirming you are running the stock tire size...

Other possibilities are: previous owner swapped the rear end and didn't recalibrate the ECU, or swapped the ECU, and again, didn't recalibrate it to the correct gear ratio. Who knows?

 

[Marky Dissod]

... speedometer is 10mph off ...

At what actual MpH is your speedometer off by 10MpH?

If it's ALWAYS off by 10MpH, that's the needle's stepper motor, methinks.
Even if it's not, your'll likely need to pull the driver info center out of the instrument panel.

If it's off by 10MpH at a certain MpH, less under that MpH, more over that MpH,
that's either your tires, or your pcm tune, most likely.

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

You are already receiving sage advice from the knowledgeable folks on this Forum.

 

[PanchohasAyukonno]

Are you running a different size tire then stock?

Running equivalent size to stock.

 

[PanchohasAyukonno]

At what actual MpH is your speedometer off by 10MpH?

If it's ALWAYS off by 10MpH, that's the needle's stepper motor, methinks.
Even if it's not, your'll likely need to pull the driver info center out of the instrument panel.

If it's off by 10MpH at a certain MpH, less under that MpH, more over that MpH,
that's either your tires, or your pcm tune, most likely.

Using gps it says I’m going 70 but the speedometer says 80 with the scanner I have ecu says I’m going 80 and with a car pacing me actual speed is 70

 

[PanchohasAyukonno]

You just bought the vehicle? Do you know the history?

Agree on confirming you are running the stock tire size...

Other possibilities are: previous owner swapped the rear end and didn't recalibrate the ECU, or swapped the ECU, and again, didn't recalibrate it to the correct gear ratio. Who knows?

Yeah just bought it so I know nothing about it what’s been done to it, everything seems to look stock other than air intake and a spacer lift in the front

 

[PanchohasAyukonno]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

You are already receiving sage advice from the knowledgeable folks on this Forum.

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

You are already receiving sage advice from the knowledgeable folks on this Forum.

 

[PanchohasAyukonno]

Nothing has been done to it by me other than trying to color match the stock black grille and the fog light housings

 

[Marky Dissod]

Using gps it says I’m going 70MpH
but the speedometer says 80MpH
with the scanner I have ecu says I’m going 80MpH
and with a car pacing me actual speed is 70MpH

Speedo in the driver instrument cluster reads fast,
ECU says same as DIC-speedo,
and GPS & some other car says actual?

Your ecm needs to be reprogrammed.

 

[PanchohasAyukonno]

Speedo in the driver instrument cluster reads fast,
ECU says same as DIC-speedo,
and GPS & some other car says actual?

Your ecm needs to be reprogrammed.

How would I go about reprogramming? Where do I start?

 

[Marky Dissod]

Unfortunately, best bang for your buck would be to have both your ecm & tcm tuned.
BlackBear Performance comes highly recommended here, but there are other tuners with good reputations.
Do your due diligence before getting your vehicle tuned.
'Best bang for your buck' does not mean 'cheapest'.

Hang on a sec ...

Are you running a different size tire then stock?

Running equivalent size to stock.

Pray tell, what is the actual size of the TIRES on your Yukon?
Is this the same size as the tire size mentioned in the door?

If it's not, and your ecm & tcm have already been tuned, then you should ask the previous owner who the previous tuner was.
Updating a tune is always cheaper than a fresh baked tune.

 

[PanchohasAyukonno]

Unfortunately, best bang for your buck would be to have both your ecm & tcm tuned.
BlackBear Performance comes highly recommended here, but there are other tuners with good reputations.
Do your due diligence before getting your vehicle tuned.
'Best bang for your buck' does not mean 'cheapest'.

Hang on a sec ...Pray tell, what is the actual size of the TIRES on your Yukon?
Is this the same size as the tire size mentioned in the door?

If it's not, and your ecm & tcm have already been tuned, then you should ask the previous owner who the previous tuner was.
Updating a tune is always cheaper than a fresh baked tune.

That’s where I’m hurting I’ll give you the size I have on now later today and what the door says as well, I can’t contact previous owner because I got it at an auction