Mine will occasionaly decide it doesn't want to hold the pedal for me either. Very sporadic, but when it happens, turning the engine off and starting it again does the trick. It's aggavating if you've just got on the interstate or just got up to speed on the hwy. Mine acts as if nothing happened-no functionality, no "cruise" light on the dash either.
There are a lot of non-urgent PCM codes that will disable the cruise control as an annoying "hint" to get things looked at. Not urgent enough to light up the service engine soon lamp, but they store codes in memory. The PCM also stores the last few reasons that the cruise control shuts off, like brake pedal, overspeed, etc.
That can help troubleshooting intermittent issues. But most parts stores scanners won't report those memory codes. You may need a dealer or a high-end independent mechanic with a scan tool to look deeply into the PCM memory.
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