OK, that explains it. On these PCM's the housekeeping transmission keeps on coming even if you are sending requests. They are very short (typically a byte or two) and come between the regular returned data, or worse yet, atop your request string. And by the way, it doesn't silence the other modules; it silences the pcm. The ABS and other secondary modules are all slaved to the pcm and don't send out any housekeeping.