Unintended Result-------Tire Circumference

[Mad Horse]

Hello Everyone,

I recently installed Dark Horse HP wheels and tires on my PP GT with a 6MT. I made changes to the tire circumference using Forscan and got it to within 1 MPH at 80 MPH so I was pretty happy with that result. I made the changes in the non as built BCM settings to make it easier. Now I've noticed I can't engage either adaptive or regular cruise control when in 6th gear. Works fine in 5th and lower. I saved the original configuration so I'll go back to that once the weather around here clears up to see if that fixes the issue. I'll try the as built settings if it does.

I've noticed the non as built easy settings seem to give some unwanted consequences. I tried turning auto start/stop off but it gave me a battery light on the dash. Not surprising since it's listed as BMS/auto start stop.

Any input from you guys is greatly appreciated.

Sponsored

 

[REV745DH24]

Does this happen before the Forscan or after the Forscan?
I have been reluctant to use Forscan to mess up with the computer system in the car! Actually I really have not investigated the Forscan but from my experience as retired computer analyst myself, I would leave my system alone and not mess around with triggering somethings in the system! I maybe wrong about the Forscan for those who have been an expert in Forscan, then I would have let the Forscan expert do it! You could tell the Forscan expert what went wrong and they will have to rig the system for more improvement! Don’t get after me for opinions, that is just saying of my opinions! Hope someone really expert in Forscan can help you fix it! May the best of good luck be with you!!!

 

[Mad Horse]

I believe it happened after I set the tire circumference. I'll go back to the as built and see if that fixes it.

 

[Fruitstang]

Is your new circumference smaller or larger than the original one?
Some people have the idea to reduce the value in the hope the speed limiter then allows higher wheel rotation speed and then in reality faster top speed.
Maybe you just reduced too much so the system thinks you want to cheat.

 

[npole]

There's two general rules: you can't use "too high" or "too low" numbers there, despite it accepting anything, there's certain limits (which are currently unknown for a specific car). Second thing, you have to reset the PCM and TCM modules to have them "re-learn" the new circumferences or there will be unpredicted behaviors and it will start to throw errors.

 

[Mad Horse]

There's two general rules: you can't use "too high" or "too low" numbers there, despite it accepting anything, there's certain limits (which are currently unknown for a specific car). Second thing, you have to reset the PCM and TCM modules to have them "re-learn" the new circumferences or there will be unpredicted behaviors and it will start to throw errors.

This is what I was thinking. I'll give it a shot tonight.

Also, I found that simply turning the ignition off then on isn't enough to make the changes take effect. I'm not sure this car is ever completely off. I started to disconnect then reconnect the battery after a change and this worked 100% of the time.

 

[Mad Horse]

There's two general rules: you can't use "too high" or "too low" numbers there, despite it accepting anything, there's certain limits (which are currently unknown for a specific car). Second thing, you have to reset the PCM and TCM modules to have them "re-learn" the new circumferences or there will be unpredicted behaviors and it will start to throw errors.

I'm basically going to the Dark Horse HP numbers. Circumference of the new tire is 2040 mm which gets me to within 1 mph at 80 mph. I'll take that. The hex is 07F8.

 

[Mad Horse]

Is your new circumference smaller or larger than the original one?
Some people have the idea to reduce the value in the hope the speed limiter then allows higher wheel rotation speed and then in reality faster top speed.
Maybe you just reduced too much so the system thinks you want to cheat.

I think the original value was 2187 mm. I've set it to 2040. I'm using a 305/30-19 in the rear.

 

[npole]

Reset the modules and it should work without throwing errors as those numbers will fall within the accepted numbers (unless they are different for any PCM, according to the original specs... but I don't think so). Mine (EU DH) is set to 0882 HEX.

PS:do you know anything about the APIM module? (7D0-07-03)

 

[Mad Horse]

Reset the modules and it should work without throwing errors as those numbers will fall within the accepted numbers (unless they are different for any PCM, according to the original specs... but I don't think so). Mine (EU DH) is set to 0882 HEX.

PS:do you know anything about the APIM module? (7D0-07-03)

No. I'm new at this. What should I know?

 

[npole]

No idea, that's why I've asked. It refers to the tires circumference as well, but AFAIK the APIM is only responsible of the interface, so I don't know what's about... that's why I've asked if you know anything about it. Maybe it's the size of the wheels on the screen (I'm joking but you never know.. ).

 

[Mad Horse]

Success!!! I reset the TCM/PCM modules and the speed is now within 1 mph at 80 mph (as it already was)and cruise works while in 6th gear (which it didn't before the reset).

Thank you all for helping this newb out! What a great resource!

Sponsored