Where is the speed setting STORED for the cruise control?

[pontifex4]

This is on a 2004 Cayenne S Titanium.

 

Question:  Where is the speed setting for the cruise control stored, i.e. in which module? 

When you press the end of the stalk to set cruise control, that value is saved until you turn the car off.  That value must live somewhere.  Where?

 

My issue: 

• When driving, the cruise control will periodically cancel AND forget its setting
• The cruise control icon on the dash turns off when this happens, then immediately back on
• No value is stored in the cruise control afterward (i.e. "resume" doesn't work, I have to set the speed again by pressing the "set" button at the end of the stalk)
• The steering wheel button lights also blink once when this happens (the ones which are toggled with the redundant buttons on the back of the wheel at 9:00 and 3:00)
• Notably, if I turn those same steering wheel lights off BEFORE one of these events, they turn on AFTER the event, regardless of the setting before the event, as though there has been a reset of that module

 

To me, this points to a module that stores information that doesn't persist through a restart (i.e. key turned off, then car started).  If I can figure out which module that is, I can be more targeted in my search for the cause.

 

So far, I've tried (unsuccessfully):

• New brake pedal switch
• New battery and cleaning battery contacts as well as grounds near battery (so far only those)
• Re-soldering harness splices in driver's footwell/dead pedal area (two were marginal)
• Fully charging battery with a CTEK 4.3 (battery drain has not been an issue)

 

 

[GSpence2]

If I am not mistaken CC control inputs would be stored in the DME. If yours is acting up you may have a DME with an internal short or coding issue. Hopefully you only have a bad switch as opposed to needing a new DME.

[pontifex4]

On 12/31/2020 at 5:47 PM, GSpence2 said:

If I am not mistaken CC control inputs would be stored in the DME. If yours is acting up you may have a DME with an internal short or coding issue. Hopefully you only have a bad switch as opposed to needing a new DME.

 

Thank you, I hope I don't have a bad DME!  Notably, everything else works fine, I haven't changed anything except the battery, so I don't suspect improper coding.

[Loren]

Sometimes when there is a voltage spike to the system (like connecting a new battery) the programming can get "mixed up". When this happens the best thing to do is have a tech/shop with a PIWIS re-program the affected control module(s). I think it very rare to replace a DME if most everything but one or two items are not working.

[pontifex4]

Thanks, Loren.  I hadn't heard that -- I'll see if I can find a shop with a PIWIS near me.