How to fix the fast reading speedometer error on your mk5 Jetta, Golf or Rabbit (may also apply to mk6 Golf)
difficulty: 1/5
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Introduction

German cars allow a small percentage reading fast on the speedometer but not reading slow.  The mk5 Jetta, Golf, and Rabbit (includes the GTI/GLI) have ridiculously fast speedometers which should have been fixed by the dealer under warranty.  This may also apply to mk6 Golfs and Golf wagons (Jetta sportwagen in the US).  The error may be higher or lower depending on wheel packages and in some cases, is as high as 10% too fast.

The speedometer has a correction factor which results in the signal from the speed sensor being read differently at the speedometer vs. odometer.  If the odometer read fast VW could be sued for cheating people out of the factory warranty by shortening it (has happened in the past with various car makes).  If the speedometer read slow VW could be partially responsible for your speeding ticket.

There were a few early North American cars with instrument clusters mistakenly coded as European tire but most of these were fixed.  See this TSB in .pdf format for more details: European coding change.

Different tires/wheels can change the speedometer and odometer reading by changing the rolling diameter.  Take this into account when considering the speedometer and/or odometer error.  See 1000q: wheel/tire calculator to see some examples.

Unlike earlier cars, there is no speedometer sensor on the transmission.  Mk5 Jetta read the speedometer signal from the wheels.  I'm not sure if adjusting the speedometer will also adjust the odometer.

Parts

VCDS cable and software from ross tech

Procedure

NOTE - GPS are pretty accurate driving on a straight and level road at a constant speed so under those conditions, I'll call the speed displayed on the GPS "actual speed."  What the speedometer or climatronic shows is "indicated speed".

First determine how fast your speedometer is reading.  The easiest way is to find a flat stretch of road with a handheld GPS to measure actual speed.  While not as accurate, you could also note mile markers over a long, straight road and divide by elapsed time.  If you have dual zone automatic climate control, access the menu to show speed.  If you don't have dual zone auto climatronic, you cannot access this menu.  See 1000q: climatronic menu for more details.  The climatronic speed may be different because of the speedometer correction factor.  To correct the speedometer, change the correction factor.  This has no effect on the climatronic speed or odometer.

While stopped, plug the VCDS cable into the obd2 port and start the software.  Click on "17-Instruments".

Click on "Coding - 07"

The highlighted code is the instrument cluster code.  Change the last digit, the distance impulse number (in this case 4) to 1-7.  In this example, lower than 4 will make the speedometer read faster and higher than 4 will make the speedometer read slower.  My speedometer was reading about 10% fast so I changed the last digit from 4 to 6.  Click "Do It!".  It should say that the code was accepted.  Double check that it's still there.  You should also see the new code in the screen above.  The final result is a speedometer that reads within 1 mph of what I believe is actual speed.

 

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