Speedometer Showing Wrong MPH

[dretwenty5]

My speedo is about 12 mph off, how can I get this fixed. Would the speedo effect the odometer readings as well.

[eldorado99]

Yes it will affect odometer readings, first you need to figure out why your speedo is off. Are you using non stock sized tires?

[Red_October_7000]

Put the factory wheels/tires back on it.
Seriously if you have changed them this will do it quite readily.
If you have the stock size, at least, then you have another issue. Is it a consistant 12MPH? Which direction? Digital dash or analog?

[ewill3rd]

On old cars with cable driven speedos, the odo ran off the speedo.
Nowadays the PCM sends pulses to the IPC and the IPC ticks off the miles and runs the speedo based on the same signal.

As stated above, what tire/wheel combo have you got?

Speedos are off by a ratio, that means it is not 12 mph off, but 12 mph off at a given speed. At lower speeds it will be less, at higher speeds it will be more.
Are we talking at 60 mph or something?

[dretwenty5]

I have the factory tires and rims on there. At 60 speedo reads 48, at 65 its 52. Digital dash.

[misfit6794]

Sounds like you are having a wheel speed sensor failure. Is your traction control and abs working properly?, or do you have any warning lights for either? They both need the speed sensor to be working to function correctly. Did you drive through a deep puddle of water? Thats almost always the reason wheel speed sensors go bad. The fact that your speedo is only a little off,relativelty, makes me think its getting a bad reading from one of the wheels. Hope this helps.

[JTraik]

Are you off by a percentage or off by an integer? Sounds more like a percentage. Did you swap gears in the rearend or anything like that?

[dretwenty5]

The car is completely stock, the ABS has started to come on once in a while though.

[Rob Benham]

I assume that the pulse is taken from one or more of the detectors on the ABS system. Is this correct? If so, have you tried wire brushing the castellations on the hubs? Some of mine were clogged with disc metal particles.

How are you checking the speed...GPS?

[dretwenty5]

The speed is being checked by a radar gun. The ABS code is for the front right wheel speed sensor.