darksky

Does anyone know if the speedometer and the odometer get their "speed" data from the same source or are there multiple sensors that record vehicle speed in a 2008 TL? I got two different answers when I called two different dealerships

LukeaTron

Most cars, certainly every Honda I've ever poked at, counts the rotations of the outer carrier of the differential. No matter what the split the differential is putting out, the carrier gear is always the average of the two.

Tripnbeats

every wheel has a speed sensor the tranny has a speedsensor the engine has a timer

KaMLuNg

iTrader: (5)

VSS that is recorded through the ECU...

BLACKURA_NY

iTrader: (6)

curious... why ya wanna know? ...smells like somebody wants to put a odo' switch in lol j/k

Bearcat94

I think he's still trying to figure out why his Speedo say's 70, but his TC average speed says 66 (or whatever).

darksky

@Bearcat94 - yep! The official word from Acura is that the trip computer isn't meant to be used this way. It's only meant to be reset at a gas fill up. There are many examples of folks setting their cruise control and THEN resetting the trip computer. As you know, the average speed of a constant IS THE CONSTANT!

I'm thinking that if the trip computer gets it's speed info from a sensor that's different than the sensor the speedo is using, that would explain the 4 MPH discrepancy. I also think that would imply that my odometer would be off by that same amount unless there is a third and unique sensor that supplies the distance data.

Trying to get a straight answer from Acura either from the customer care 800 number, for from speaking through the mechanics at my dealership is impossible

MWalsh9152

one easy way to test your speedometer accuracy would be to grab someones GPS if one is available and take it out and check Mine is dead on according to my Magellan. It wouldnt answer your questions about the trip computer, but at least you will know your odometer isnt off

darksky

Right you are. I did this and indeed it's off by about 3 %. I also confirmed it by traveling a known distance and timing it. Both methods show about a 3 % error. Does it matter? Perhaps not in the grand scheme of things, but I can be OCD about these things. I have to do the experiment on the odometer on a long road trip (>100 miles) so that'll have to wait.

Bearcat94

OK, darksky, did a little experiment for you.

Found a *fairly* level stretch of freeway. I had at my disposal the TL MID Trip Computer, Speedo and Cruise Control as well as a portable Navi with instantaneous Speed and Trip Computer.

I set the Cruise to a hair over 70 according to the speedo. I reset the MID TC and the Portable Navi TC at the same time (I had a helper). I then monitored instaneous speed on the Portable Navi.

Over approx 5 miles on Cruise, the Navi instantaneous speed was consistently 71 MPH. There were a couple of very brief moments where it showed 70 or 72, but the vast majority of the time stayed at 71 MPH.

That puts the Portable Navi pretty much dead nuts to the speedo.

At the end of the ~5 miles the TC on the Portable Navi reported an average speed of (surprise) 71 MPH. The Acura MID TC, over the same period, reported an average speed of 68 MPH.

The only thing I noticed was the MID TC took, say, 20 seconds from the time of reset until it displayed a speed. The very 1st average speed displayed was 68 MPH and it never changed.

So, the MID TC is consistent at a constant speed, but it doesn't record the "right" speed as compared to the speedo and an accurate external source.

darksky

@Bearcat - thanks for doing the experiment! This is exactly the kind of data I wanted to see for someone else's TL.

To recap my data: I set the cruise @ 70 MPH, reset MID and used a Magellan 4000-something GPS as an independent speedo (it was tracking 9 satellites at the time). After traveling 6 or 7 miles, the MID showed 66 MPH as the average speed and the Megellan, although it doesn't calculate a formal average, bounced around between 68-69 MPH throughout the trip.

I also did the stopwatch experiment; traveled a known distance based on highway mile markers and timed the trip w/ a stopwatch. I found that when my cruise was set @ 71 MPH, I was traveling about 69 MPH. This result is consistent with the GPS data.

The only experiment I need to do now is wait until we go on a long roadtrip of >100 miles on the same highway, and reset my odometer at a known mile marker, then compare the distance traveled to my odometer. This experiment will prove to me that either the error in the speedo is also in the odometer, or the odometer has its own error that differs from the speedo's error (in other words, is the TL using independent sensors for the speedo and odometer) - pointless exercises to some, but valuable information to me

Anyway, thanks again for the data!

Bearcat94

darksky, we've got a lower level Magellan (3200) and it has a TC. The 40xx should too.

If you get to use it again, check "User Options" from the main menu and then "Trip Computer". If you find it, it should have "Reset", "Stop/Start" and "Save" functions.

darksky

Thanks for the info, bearcat. I don't have access to that particular one any more. I'm very happy to use a stop watch and the highway mile markers. I have done this at several different speeds now and found a consistent 3 % error (reads 3 % too fast).