Speedometer off after gear change
11-18-2018, 03:02 PM
#1
Intermediate
Thread Starter
Speedometer off after gear change
Hey guys I have searched and found nothing. I have a 2002 vert with an a4 tranny that I changed from 2:73 to a 3:15 differential. I got the 3:15 at a great price and it works great that’s why I didn’t go with the 3:42
My problem is now that it is done my speedometer is off. When I am driving 75 mph my speedometer is reading
66 mph. Everything I have read says the speedometer should not be affected by the change.
When we did initial test drive the abs,tc and ah lights came on after a hard launch but, the dic reads tcs-28 1 code but there are no active codes to research, I’ve checked fuses, grounds etc with no change.
Thanks in advance Fleet
My problem is now that it is done my speedometer is off. When I am driving 75 mph my speedometer is reading
66 mph. Everything I have read says the speedometer should not be affected by the change.
When we did initial test drive the abs,tc and ah lights came on after a hard launch but, the dic reads tcs-28 1 code but there are no active codes to research, I’ve checked fuses, grounds etc with no change.
Thanks in advance Fleet
11-18-2018, 05:19 PM
#2
Le Mans Master
Member Since: Jul 2008
Location: 200 AGL
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St. Jude Donor '15
You just need to have your PCM retuned. Changing gear ratios absolutely requires a retune. This will clear your other lights related to speed sensor as well.
11-18-2018, 05:58 PM
#3
Le Mans Master
3.15 / 2.73
75 / 66
Same result(ish)
You need a tune
75 / 66
Same result(ish)
You need a tune
Last edited by grantv; 11-18-2018 at 05:59 PM.
11-19-2018, 01:06 PM
#6
Melting Slicks
Find a friend locally who uses EFILive or HPTuners or anyone with Bi-directional scan software that will change wheel size and rearend ratio (very few do this). I should cost you about $100 to have this done. Many vendors who do mail order tunes can also include it when they make the changes to the PCM.
11-19-2018, 03:49 PM
#8
Melting Slicks
your speedo is not off because you changed gears. You do need the tune because you have a auto trans, TCC slip table and the WOT shift MPH value need adjustment, your shift points will be off. The speed sensor reads off the axle output not the diff. the only thing that affects speedometer calibration is tire diameter. I went from 3.42s to 4.10s no change in speedometer readings
Last edited by feeder82; 11-19-2018 at 04:26 PM.
11-19-2018, 04:54 PM
#9
Intermediate
Thread Starter
Thanks for your reply feeder82. It’s funny my tires are stock,I only changed diffs because it was cheap.
I use to live in Peewaukee Wi.Not missing the weather right now.
I use to live in Peewaukee Wi.Not missing the weather right now.