Does anyone know how the on board computer monitors average speed? I hit a huge pothole yesterday destroying two forged BBS wheels. I noticed that the average speed reading is now 00.0. - it was at 48.7mph Just wondering if the two events are related.

Michael

 

I don't know, but it may take its impulse from the flat tire monitor which in actuality compares tire rotation speed. If you severed or dislodged the sensor wire on a wheel, it will assume the wheel is not rotating. Has your flat tire indicator also illuminated?

You can reset the average speed and average mpg by scrolling to those settings and press/holding the trip computer button (I do this at each fill-up).

You should reset the flat tire monitor anytime you move or adjust wheels/tires. Do so by turning the car to accessory, press and hold the flat tire monitor button until the dash light stays lit, then start the car and wait for the light to go out.

 

Okay, thank you - good advise by the way.

The flat tire monitor did ot come on despite a bulge in the sidewall; the system was sensitive enough to recognize a 3 psi difference between front and rear tires during a recent experiment.

Michael

 

the abs sensor can ouput vehicle speed and they are sometimes flakey. it's a simple plug in unit on each wheel.

 

ABS sensor huh? Interesting.

I used to try to use it on the E46 but never found the info all that useful as it would not seem ot stay on for protracted periods and continue to calculate the average speed. (The 3er does not have a flat tire monitor so I doubt the two are related.)

 

...perhaps it came loose...


Thanks all.

 

The ABS Sensor at each wheel is for ABS, ASC, Tire Pressure Monitor. The Spedometer and Trip computer (speed and avg speed) do not get their reading from the ABS sensors. Those come from the tansaxle. (look for the tamper resistant locking plug on the tranny)

ABS Sensor: Measures the speed of a wheel. It consists of gear-shaped sensor rotor and a sensor element. The element contains a bar magnet around which a coil is wound. The sensor is installed on the back side of the brake rotor. Sine-wave current is generated by the sensor as the wheel rotates. The frequency and voltage increase(s) as the rotating speed increases.

The ABS computer figures out the speed of the wheels, if a wheel starts to slow down faster than others, ABS kicks in. If a front wheel goes faster relative to the other front wheel, the computer kicks in and brakes the spinning wheel, or retards the engine. (add a yaw sensor and you have DSC).

The tire monitor, monitors the speed from all four sensors, if there is a rotational speed difference of longer than a few seconds, the tire monitor light comes on. This is why the tire monitor sometimes comes on during wheel spinning launch or very hard braking.

If an ABS sensor is lose or unplugged, the ABS warning light will light up indicating a fault in the system. (may also light the tire monitor, but not without the ABS warning).

Steve

 

as a side note, check inside your egine bay where the the front struts mount to the car. Hitting a pot hole that large is bound to "mushroom" the mount that should be flat. It's an easy fix but you don't want to drive around with them like that. Sorry about your wheels.

 

SoCalJCWMini,

I checked and both sides appear to look the same and feel the same. I placed as much up and down pressure on the front end while watching these to see if all was well. The alignment is off noticably, no surprise and the ball joint is a wee bit loose. Tomorrow I'll check everything more thoroughly.

I'm very surprised both tires aren't damaged - visibly they both look fine. Front rim is bent on the outside portion of the rim and the rear is bent on the inside portion of the rim.

Nearly $600.00 each!

 

mielnicki: correction noted...thx

 

My average speed is only 31 mph!

Go speedracer go!

 

...I probably drive faster than one should on public roads...gotta get to a track.

Front end fixed...two new wheels on Wed. I'm happier today.