aliljet

I've got a 2007 accord which is in great condition and for some reason the speedometer is undereporting my speed by 10-15 mph at highway speeds. I'm using stock tires (well, recommended tire sizes thanks to Costco) so there has to be something else wrong.

While researching this, it looks like there's some kind of vehicle speed sensor that could be screwed up, but I have no idea how this system works.

Can anyone describe how this system is put together? And can anyone talk about how speedometers can get out of calibration and how one can recalibrate them?

This is an odd problem and I could use your help! Thanks!

MSchu

it's more than likely the tires aspect ratio...

aliljet

Nope, I can guaranatee that's not the case. I think it's some combination of sensors that are screwed up. I really don't understand how the speedometer is reporting my speed. How does the ECU send a speed to my speedometer? How does the ECU even calculate my speed? Yuck..

LPED

AFAIK, there a output speed sensor (this is basic magnetic sensor like ABS wheel sensor) thats mounted over the rear of tranny and senses the output shaft speed (axle speed) . the sensor works on pulses and info goes to ECU and then to Gauge cluster .try unhooked the 3 wire plug ,maybe bad connection .
There a self diagnosis Gauge module test , thats tests all indicator lights and gauges (gauge meter should do full sweep).
Best to get/borrow a manual and check for any codes while your at it .

SO your saying your tires match the size on door sill ?
whats the size thats on the front ?

aliljet

Do you have any kind of schematic/drawing kind of thing that would help direct me to the location of this? I can't seem to find this myself..

Can you describe this in a bit more detail? I'm not sure what you mean... how is this test executed?

Yes, absolutely.

LPED

Here, pretty sure its Part 11, or 12

https://www.hondapartsdeals.com/hpa_...nGroupID=11940

The test procedure is long I have doc for Acura 04-06 which is probably same for Honda . Thats why I said get a hold of manual .

I try an copy/paste procedure here .
Edit PDF won't allow it .

aliljet

How do you know that 11 and 12 are the ones that generate the speed information? Doesn't this kind of information come from something closer to the wheels? Does the ECU look at any information from the ABS sensors?

LPED

Thats only pic online I can show you . AFAIK the countershaft sensor(outputshaft sensor) is used for vehicle speed. I know in testing it it will show vehicle speed on HSD tester .
wheel sensors are used for ABS/VSA , I never heard using wheel sensor for vehicle speed .

My comment on the sensor was just to disconnect the plug and reconnect as could be poor connection . I would first check for any stored codes .

I don't know if color codes are same but my acura gives these color code wires for countershaft wires .

1)Yel/Blu
2)Blk/Blu
3)Brn/Yel

I have to say that IMO if this goes bad I would expect more of a intermittent speedo or sporadic operation, not smooth speedo operation at some reduced % reading .
Again would throw a code most likely . P0720 or something

Ross 2.0

This could only be one of two things. Either a bad speed sensor or a bad gauge control module.