The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - Q- speedo off & bad MPG

46stude · 12-26-2016, 10:58 PM

We have an '02 Suburban 1500, 2wd, 5.3L. It's got somewhere around 230K+ on it, & we've had it since 198K. It's stock, with 265/75/16s, which are just a touch taller than the factory 70s.

It's always got poor fuel mileage, & I discovered a long time ago that the speedometer doesn't read correctly. According to a couple GPS speedo apps I've tried on my phone, it's off by about 6-7 MPH at highway speeds, less as speed decreases. Rough guess of MPG (since the odometer isn't accurate) is the thing averages 10-12. Oh, & no SES lights.

I've tried lots of searches on the web, but everything goes to the dreaded cluster failures. That's not my problem, as far as I can tell.

The only thing I can figure is maybe the PCM needs a factory reflash. No idea how or why it would be outta whack, but there's nothing else I can think of that'd kick the speedo out like that. Any other ideas, or similar problems somebody knows a fix for?

12-26-2016, 10:58 PM	#1
46stude Registered User Join Date: Dec 2014 Location: Rockport, Texas Posts: 192	Q- speedo off & bad MPG We have an '02 Suburban 1500, 2wd, 5.3L. It's got somewhere around 230K+ on it, & we've had it since 198K. It's stock, with 265/75/16s, which are just a touch taller than the factory 70s. It's always got poor fuel mileage, & I discovered a long time ago that the speedometer doesn't read correctly. According to a couple GPS speedo apps I've tried on my phone, it's off by about 6-7 MPH at highway speeds, less as speed decreases. Rough guess of MPG (since the odometer isn't accurate) is the thing averages 10-12. Oh, & no SES lights. I've tried lots of searches on the web, but everything goes to the dreaded cluster failures. That's not my problem, as far as I can tell. The only thing I can figure is maybe the PCM needs a factory reflash. No idea how or why it would be outta whack, but there's nothing else I can think of that'd kick the speedo out like that. Any other ideas, or similar problems somebody knows a fix for?