S70 AWD model year 2000: At random times while driving with cruise control engaged, usually at highway speeds, the cruise control stops holding speed and the "CRUISE" indicator on the instrument panel goes out. When this has happened, an attempt to re-engage by pressing the "+" end of the "Set" rocker switch or moving the Cruise Control Switch to the "Resume" position may cause cruise to re-engage but always for only a second or two; sometimes those attempts have no effect. In each instance, repeat tries after the third attempt all have no effect. After continuing to drive without engaging cruise control for fifteen minutes or more, an attempt to again engage the cruise control have usually been successful (although on one recent trip, attempts every ten minutes all failed). After each instance of failure, when cruise control was again engaged successfully it continued to operate properly for several days and numerous trips before dropping out once again. Dealer readjusted the brake pedal position sensor, but the drop-out behavior repeated the next day. Dealer repeated diagnosis after that but was unable to determine a cause or suggest a fix. I suggested to dealer that this behavior sounds to me like a computer problem, perhaps with Electronic Throttle Module. Service rep replied that technician had considered all possibilities, then told me that they can not just start replacing things one at a time until something works. The skeptic in me wonders whether they might not agree about the ETM, but want me to wait until my S70 exceeds the 100,000 mile limit of the new "specially extended" warranty. (That will be just 9000 more miles)
Can anyone offer help or advice? Can anyone provide a description (like for example a logic diagram) of what systems and signals have input to the cruise control so I might get a clue as to what is causing this intermittent problem?
Thank you.

 

Well first of all since you found the problem before the warranty expires, it should be under warranty after the 100K. The most common problem with cruise control is a vacuum leak, but a dealer would certainly know that and would have checked it out.