speedometer reading off

Discussion in 'Technical' started by Unregistered, Jul 4, 2012.

  1. it reads like 20mph too fast. replaced the vehicle speed sensor, no luck.

    it's a 96 chevy 1500 truck, v8, rwd.

    any ideas? posted this on a chevy truck forum but no one even replied, I know there is a couple of people on here really familiar with these trucks, though i'm afraid they don't post here anymore...
  2. do you have the standard size rims/tires on the car?
  3. yes. but even if i didnt would it read wrong by that much?

    the rims are the OEM, the tire size is what it supposed to be...
  4. if they're what they're supposed to be it shouldn't change it. however if they put the wrong sized tire on it can change it by that much.
  5. is it 20mph out at all speeds or does it get worse as your speed increases?
  6. Someone could have changed the rear end gears maybe.

    You should be able to recalibrate via OBD-II, no?
  7. I'm not too sure about this, so someone tell me if I'm off the mark, but your on board computer will log certain data but will always have a set value from the manufacturer, therefore if you lose power to the module the data is reverted back to its original value.

    Just thinking it might be the control module, if you just replaced the sensor and the problem still persists, then I'm guessing it's the module.

  8. The stealership can recalibrate your speedo for about $20
    A handheld tuner can do it and more for $250ish
    Jet makes something that will let you do speedo and shift points for $150
  9. A lot of speedometers are 5-10% positive or something. So if you're doing 300 mph and it's 20 off, there's nothing wrong with your truck.
  10. lol, yeah that's probably what it is moo.
  11. Yeah I called my dad and told him it's normal
  12. The tires are the right size, I guess someone switched out rear ends or something. Going to have a dealership recalibrate the speedo
  13. Well, by the 90s, the speedo would be electronically controlled by the computer. Simply put, it could be a problem with the sending unit. A start would be simply hook into the obd and monitor what the computer is saying the speed is. Remember a speedometer is just a voltmeter. If the computer is saying speed is one thing, and the speedo is saying something else, the problem is between computer and speedo. If computer is reading wrong as well, it might be the the sending unit.

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