Speedometer jumping....

[JD525IA]

Whilst on a 20 mile quick trip yesterday morning, I set the cruise control to around 80mph. After a minute, the car seemed to lurch, like someone was hitting the accelerator quickly. I didn't have my foot on it, just near it. I did notice the speed jumping between 78 - 81 very rapidly. Strange thing is that when I disengaged the cruise control, the speedometer stayed rock steady at whatever speed I was at. Only jumped around when the cruise was on.

Does this sound like my speed sensor is going out? How come it only would start acting up at higher speeds with the cruise control on?

Is the sensor that provides your MPH readout mounted on top of the rear differential?

Suggestions, please.

JD

[JD525IA]

and after reading everyone's replys, it looks like I do need to replace the sensor at the differential.

[Jon K]

I sometimes have an issue with my speedometer rocketing up, but it's usually because my rear wheels are spinning really fast.

[Rustam]

Strange thing is that when I disengaged the cruise control, the speedometer stayed rock steady at whatever speed I was at. Only jumped around when the cruise was on.

Does this sound like my speed sensor is going out? Suggestions, please.

JD

I wouldn't imagine that the sensor is at fault if the speed is shown consistently - which is exactly what you are telling here.

[BillionPa]

cruise control module borked?

[gale]

It could likely be the sensor which may or may not be bad. They accumulate ferritic "fuzz" on the tips of the sensor that straddle the toothed wheel inside the diff & removing them & wiping them clean usually takes care of it. They're a pain in the a$$ to change with the diff in the car, so if you're going to the trouble of removing the sensor, just buy a new one. They're around $32 on-line.

http://img.eautopartscatalog.com/live/P401937882OES.JPG

[JD525IA]

I'll look into it.

[GoldenOne]

i have that same problem also, doesnt happen all the time so I tend to ignore it...

[materiamage]

Check out my thread here, I plan of tracking it down and then doing a write up on the fix.

hope it helps.

~RB

http://www.bimmer.info/forum/showthread.php?t=21433