Reprinted from FMCA:
This might be helpful to folks with cruise control problems associated with the C7/C13/C15 Cats.
The article is HERE
It began as a common problem: cruise control would not latch.
Lots of owners have commented about having to cycle their Smartwheel Cruise Control ON/OFF switches before latching can occur.
Then, another oddity: turning the dash lights rheostat on would unlatch/disengage the cruise control.
Later, the system stopped working entirely. I could, on occasion, get it to engage for brief periods. No single event ever defined the inevitable unlatching, the longest it went without disengaging was a half-hour, during Interstate driving on a recent trip.
When I contacted our chassis tech support representative, he said such issues are usually a Caterpillar ECM problem.
Since, technically, the failure was an intermittent issue, I suspected the old culprits of corrosion, broken wires or looseness that plague all older chassis. The ECM is connected by two complex multi-pin plugs, in an area prone to spray, dirt. On the 2006 C13, it is located just forward of the fuel filter. The aft of these two plugs, taking in yellow braided wires, handles engine sensors. The smaller attends to other functions, like cruise control. I crawled underneath, used a 1/8" allen key to loosen the smaller of these, sprayed it with electronics cleaner, carefully snugged the plug into place and tightened the hold down screw.
Still, no cruise.
"It's the chassis ECM, not ours," insisted the Caterpillar shop foreman, when I raised the white flag and called for an appointment. He added that, for no charge, he'd plug in the ECM and prove his point. I hastily agreed, hung up and started driving to Holt Caterpiller of Fort Worth. They are the same folks who replaced all of my intake solenoids, accessing the engine by dismantling the bedroom closet -- they reassembled the doorframe and rehung the doors without leaving a trace -- for less than $1800.
To shorten the story, let it suffice to say the computer revealed the "Inactive" status of the cruise control, and the technician could get it latch, but only in the high-idle mode. We agreed to a road trip with me driving and him using the laptop. He threw the switches for Retarder modes, Adaptive Cruise enabling, experimented with some other ideas on the screen while I drove. Eventually, I had cruise control with unlatching anytime the engine brake power was ON or the dash lights were illuminated. For the life of me, I cannot understand the latter, unless it is an inhibit to prevent night use of VORAD, the primative adaptive cruise control with which the original RV was equipped, later decommissioned.
Finally, the technician mentioned that my brakes were showing engaged on an intermittent basis. We opened the generator bay and examined the backside of the pedal assembly. Two simple pressure switches are there: the inboard attends to cruise control, the outboard activates the brake lights. I instantly found a wobbly spade connector on the former, and when I crushed the interior slightly and slid it back into place, that line on his screen obediently said "OFF" and remained that way.
All the way home -- a trip of forty miles -- the cruise remained engaged. Now, with a long trip to Florida looming, I have the simple luxury of driving with my fingertips!