Speedometer way off

Tim Birney

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Dec 14, 2005
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05.5 TDI
IndigoBlueWagon said:
Not Jettas. Golfs are.
Coding on the 2010 Jetta is of the MKVI generation.
Ask anyone that wants to install Euro LED Tails, or the Rear Fog.

The Coding tables on the 2010 Jetta are identical to the Rabbit/Golf of 2010.

Wiring Daigrams are also different.
That is why I stated the 2010 Jettas are MKVI Chassis.
Not because the design of the outer shell was different, but because the "guts" are different.
 

dave729

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Lafayette, LA
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2009 VW Jetta Sportwagen
My 2009 is off the other way

charredwallsofthedamned said:
what about the 2010's?
I can answer about a 2009 -- mine is off the opposite of the OP -- it reads about 2-3mph lower than actual speed. I first realized that about two weeks after purchase when a cop stopped my for going 76 when I had the needle on 72.5 (what's with the marking they chose, anyway???). Validated after that with a GPS -- speed seems on the money up to about 50, then begins to show more of a difference as the speed goes up.
 

IndigoBlueWagon

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Tim Birney said:
Coding on the 2010 Jetta is of the MKVI generation.
Ask anyone that wants to install Euro LED Tails, or the Rear Fog.

The Coding tables on the 2010 Jetta are identical to the Rabbit/Golf of 2010.

Wiring Daigrams are also different.
That is why I stated the 2010 Jettas are MKVI Chassis.
Not because the design of the outer shell was different, but because the "guts" are different.
Coding may be MKVI, but the body is a MKV. At least that's what I understand from folks here. If not, I stand corrected.
 

GTIDan

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2010 Candy White Jetta, DSG
My 2010 appears to be about 1 mph fast over the digital readout. From what I've heard the digital readout is spot on.
 

abakos

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-----
GTIDan said:
My 2010 appears to be about 1 mph fast over the digital readout. From what I've heard the digital readout is spot on.
+/- 1 may as well be dead on. Tire pressure and wear combined with whatever rounding is going on in the calculation will throw it that much.

I googled and found the VCDS procedure for tweaking speedometer output too. Quite excited to mess with that this week. ;)
 

mo_focus

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We have a 2010 Golf hb and its off as well. I'm going to take it to the dealership when the time comes for its first oil change and inquire about this. 7kms is a lot to be off for a brand new car! We also tried it with Tom Tom and my blackberry GPS. Both read 120km/h and the car said it was 127km/h
 

icdoo

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We just purchased a 2010 Jetta Highline, speedo reads 100, GPS is saying 93 km. We will ask the dealer next week.
 

coolbreeze

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Took 2 1300 mile trips this month so I had a lot of time to watch the speed and my GPS. My 2009 JSW is off by 1.5/2 mph. I would show 70 mph on car speedo and GPS had 70.
 

icdoo

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Went to the dealer today, they had to call tech support and they were aware of the problem and will let us know when there is a fix. That's bull guess I need a vagcom
 

newbury

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Fairfax, VA/Fulton, MS
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2009 JSW
Took 2 1300 mile trips this month so I had a lot of time to watch the speed and my GPS. My 2009 JSW is off by 1.5/2 mph. I would show 70 mph on car speedo and GPS had 70.
Just drove from Ft. Bragg to DC area GPS 70 speedo 71.

I'm thinking of getting 215/60 R16, tires, what's the VCDS magic?
 
Last edited:

PaulGiz

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Rhode Island
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None any more. My heart couldn't take it.
Hmmm, my gps has a trip computer that I can reset at anytime. I did this and drove for about 35 miles. The car odometer read about 3 miles further than the gps trip computer.
Small variations in elevation, lane changes, jogs in the road, if short enough, are just averaged by your GPS. It is not unusual for GPS to indicate a shorter than actual distance traveled. 10% sounds like a lot, but the variance depends on the roads and terrain.

P.
 

ubercam

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2007 Golf Match TDI 1.9L (BXE) M5
On the prairies (at least around here) it's flat as a pancake.

I think the '09 is underreporting speed, which to me is not right. Speedo says 110km/h, GPS on my Blackberry says I'm going faster, but I don't recall exactly by how much, but it was a couple to a few km/h (2-5, something like that). The car is a Highline with I believe 205/55R16's. I'll measure the actual diameter with a measuring tape though instead of relying on a tire size calculator, but that's all I have to go on at the moment. I will also test with a TomTom tonight as well as do the odometer check on the Trans Canada.

I don't know what multiplier it's currently coded for, but my calculations are as follows:

tire size: 205/55R16
diameter: 632mm
circumference: 632*pi = 1985.5mm
revs/km: 503.7 (based on 1000000mm/1985.5mm)
multiplier: 503.7*48 = 24175 +/- 5 (I read somewhere the ABS sensor gives 48 impulses per revolution of the tire, and older cars with the tranny sensor gave 8 impulses/tire rev)

Does anyone know which preset multiplier choices correspond to which number in the cluster coding? If there are any corrections to the math, please let me know! I'm moving overseas shortly and would like to correct this problem for my mom. She doesn't need a speeding ticket because of a slow speedo!
 

hid3

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Lithuania, Vilnius
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tire size: 205/55R16
diameter: 632mm
circumference: 632*pi = 1985.5mm
revs/km: 503.7 (based on 1000000mm/1985.5mm)
multiplier: 503.7*48 = 24175 +/- 5 (I read somewhere the ABS sensor gives 48 impulses per revolution of the tire, and older cars with the tranny sensor gave 8 impulses/tire rev)

Does anyone know which preset multiplier choices correspond to which number in the cluster coding? If there are any corrections to the math, please let me know! I'm moving overseas shortly and would like to correct this problem for my mom. She doesn't need a speeding ticket because of a slow speedo!
At last one smart person did the calculations right, not the GPS/miles/speedo method!

Now you'll realize that there ISN'T 100% ACCURATE Distance Impulse Number for that. So VW speedometer/odometer can't be 100% accurate in either way. The 'best' setting available is 22532 AFAIK. 21848 makes speedo show faster.
 

ubercam

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My commute includes multiple lengthy portions of POKER STRAIGHT roads with negligible change in elevation, no hills, dips, bumps or anything like that, just pure flat Manitoba prairie. In this case, GPS is an acceptable and accurate alternative to a speedometer in my opinion. Sure it only shows you your speed as an integer, but it's still accurate within 1km/h which is bang on for my purposes.

I will test the car against the 10km odometer check on the Trans Canada as well as with my TomTom and BlackBerry GPS for comparison purposes. Unless I go in the middle of the night, I won't be able to time myself along the route to calculate speed because of heavy contruction on the road and flag people slowing me down at certain spots. It would just be another point of comparison to the GPS units.

Does anyone know if these are the actual multiplier values of last cluster coding digit which apply to the '09 models? I pulled the numbers from http://en.openobd.org/vw/golf_1k.htm#17

00xxx0?: Distance Impulse Number
1 - 22188
2 - 22076
3 - 21960
4 - 21848
5 - 22304
6 - 22420
7 - 22532
 

ubercam

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2007 Golf Match TDI 1.9L (BXE) M5
I checked out the cluster with the VCDS and it was coded by default to 3.

First, I used a measuring tape and a piece of wood laying across the top to measure the tire's diameter. I got 24 7/16" which is roughly 620mm. According to a tire size calculator, the diameter of my tire should be 632mm, but I'm pretty sure that's for when there's no air in it or weight on it, which is never the case when it's mounted on the car. So for now I'll use my measured diameter of 620mm since I feel it's more accurate.

I set up my laptop with VCDS and, using my TomTom GPS as a guide, I brought the car up to 100km/h and set the cruise. The GPS reported a steady 100km/h each time I tested a new multiplier. I know some of you may have certain opinions about the accuracy of GPS, but it was the best available tool I had to objectively measure my speed. If you don't agree, tough.

The results from watching the speedo needle when the GPS reported 100km/h are as follows (1-7 are the coding digits):


  1. Multiplier = 22188 : Underreports by ~3-4%
  2. Multiplier = 22076 : Underreports by ~2-3%
  3. Multiplier = 21960 : Underreports by ~2%
  4. Multiplier = 21848 : Overreports by ~5-7%
  5. Multiplier = 22304 : Underreports by ~4-5%
  6. Multiplier = 22420 : Underreports by ~6-7%
  7. Multiplier = 22532 : Underreports by ~7-8%
Those numbers are just ballpark figures based on what I remember.

Now, the fun part. I decided to watch the cluster's measuring blocks and watched 001 while driving. On multiplier #3 (21960, factory default) the measuring blocks report the car going exactly 100km/h. I sped up and slowed down and the measuring blocks were identical to the GPS for speed. Based on that, multiplier 3 is exactly what we should have for coding on these cars with 205/55R16 tires.

Going back to my calculations from an earlier post, I posited that the multipliers are the result of multiplying 48 by the number of tire rotations in 1km. I forget where I got 48 from, but it was online somewhere. Using the ideal multiplier that I derived from that assumption, I got 24643, which is about 2000 higher than the closest available coding choice. This didn't make any sense to me. How could it be that far off, yet #3 is what they set at the factory? I decided to look up a picture of an ABS ring online. I looked at one for a 2004 Jetta (site didn't have a listing for ABS rings for A5 models), so I'm assuming is still the same part. Either way, when I counted, there were only 43 slots/ribs, so 43 impulses per tire rev! Dividing the distance impulse multipliers offered as coding choices by 43 will yield exactly how many tire revs/km the multipliers are coding for!


  1. Multiplier = 22188 : Coded tire revs/km = 516
  2. Multiplier = 22076 : Coded tire revs/km = 513
  3. Multiplier = 21960 : Coded tire revs/km = 511
  4. Multiplier = 21848 : Coded tire revs/km = 508
  5. Multiplier = 22304 : Coded tire revs/km = 519
  6. Multiplier = 22420 : Coded tire revs/km = 521
  7. Multiplier = 22532 : Coded tire revs/km = 524

With that mystery solved, the issue still remains that the needle isn't pointing in exactly the right direction. From what I can tell, the needle is underreporting by about 2km/h at 100km/h and would likely just take a small turn clockwise to bring it in to where it's 100% accurate!

I'm bushed and can't think of anything else, so if you've got anything else to add, please do so!

Cam
 

ubercam

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Just some background to the math and some stuff I've thought about overnight.

My tire diameter measurement was done on the driveway with a measuring tape. I'm supposing that while the car is in motion, the tire's diameter increases slightly from centrifugal force and heat expansion. It's not beyond the realm of possibility, for, say a 2-4mm diameter increase, so let's split the difference and call it 3mm.

FYI: I used Excel to come up with these numbers, and I set the formatting for 0 decimal points. The unrounded numbers are used throughout every calculation, so they are accurate underneath, just rounded to integers for simplicity's sake. The important numbers are the % out and actual vs. coded tire revs/km.

At rest (diameter = 620mm, circ = 1948mm, revs/km = 513)
Multiplier code: 1
Ideal mulitplier: 22076
Coded multiplier: 22188
Coded revs/km: 516
Out by (%): -0.50%

Multiplier code: 2
Ideal mulitplier: 22076
Coded multiplier: 22076
Coded revs/km: 513
Out by (%): 0% (bang on perfect!)

Multiplier code: 3
Ideal mulitplier: 22076
Coded multiplier: 21960
Coded revs/km: 511
Out by (%): 0.53%

Multiplier code: 4
Ideal mulitplier: 22076
Coded multiplier: 21848
Coded revs/km: 508
Out by (%): 1.05%

Multiplier code: 5
Ideal mulitplier: 22076
Coded multiplier: 22304
Coded revs/km: 519
Out by (%): -1.02%

Multiplier code: 6
Ideal mulitplier: 22076
Coded multiplier: 22420
Coded revs/km: 521
Out by (%): -1.53%

Multiplier code: 7
Ideal mulitplier: 22076
Coded multiplier: 22532
Coded revs/km: 524
Out by (%): -2.02%

Moving (diameter = 623mm, circ = 1957mm, revs/km = 511)
Multiplier code: 1
Ideal mulitplier: 21970
Coded multiplier: 22188
Coded revs/km: 516
Out by (%): -0.98%

Multiplier code: 2
Ideal mulitplier: 21970
Coded multiplier: 22076
Coded revs/km: 513
Out by (%): -0.48%

Multiplier code: 3
Ideal mulitplier: 21970
Coded multiplier: 21960
Coded revs/km: 511
Out by (%): 0.05% (About as perfect as you can get!)

Multiplier code: 4
Ideal mulitplier: 21970
Coded multiplier: 21848
Coded revs/km: 508
Out by (%): 0.56%

Multiplier code: 5
Ideal mulitplier: 21970
Coded multiplier: 22304
Coded revs/km: 519
Out by (%): -1.50%

Multiplier code: 6
Ideal mulitplier: 21970
Coded multiplier: 22420
Coded revs/km: 521
Out by (%): -2.01%

Multiplier code: 7
Ideal mulitplier: 21970
Coded multiplier: 22532
Coded revs/km: 524
Out by (%): -2.49%

After looking at this data, I have to think that the 3mm expansion is fairly accurate. Assuming my GPS is accurate, it perfectly matches the cluster's measuring blocks showing how fast the car itself thinks it's moving. I'm satisfied with #3. BTW, I played with numbers in Excel and if the expansion is 3.28mm (total of 623.28mm), it perfectly matches the coded multiplier. I think that's close enough.

The only issue is that the needle in our cluster is about 2km/h behind what the cluster thinks it's doing. This may or may not apply to anyone else's, so please do your own testing if this topic is of interest to you. I'm not sure why the needle was set wrong (production error? done on purpose?), but luckily it's not impossible to fix. I repositioned the needle on my '02 with very little difficulty. I told my mom to remember that the needle is about 2km/h slow. I'm not sure if that's true throughout the entire range of speeds, but I told her to just assume it was. Better to be safe than sorry. I don't want to pop out the cluster and screw around with it because it's not my car, it's still on warranty and I'm leaving on Tuesday for England and if I break something I definitely won't have time to fix it.

Maybe the dealer would do the work because technically it's as accurately set as it can possibly be (AFAIK!) but the needle is just underreporting. That's a bit of a liability issue for VW is it not? I mean, without doing the research I just did, John Q. Public would have no idea it was even out. Would something like this fall under the warranty? I thought it was either their company policy or the law that the speedo can never underreport if it's properly set, or am I wrong? The funny thing is that they would have no way to view the measuring blocks without a VCDS cable and know how much to move the needle because their shop diagnostic computer isn't portable. The only other way I can think of would be to put the car on a dyno with their shop computer hooked up. Lots of VW shops have at least one VCDS cable because they can log data, especially while driving, and I know from reading around that regional VW reps carry them for the same reasons.

Anyway last day @ work and all, so I should probably finish tying up as many loose ends as possible.

Cam
 

ubercam

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2007 Golf Match TDI 1.9L (BXE) M5
I have no idea... all I know is that the car has 205/55R16's and on the driveway they were 10mm+ short of their listed diameter on the tire size calculator (www.1010tires.com is what I used) due to the car's weight and other factors. VW must have taken that into account with their selection of multipliers.
 
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