[Power Hungry]

One of the things we're starting to see more frequently on OBS trucks is difficulty in communicating with the PCM. All I can assume is that it is because the components in the PCM are aging are are starting to experience signal and timing drift which is affecting the timing critical diagnostic communications. In most communications, a drift of up to +/- 1.5% is usually acceptable although at higher data rates this often presents more of a problem. At 10.4K (J1850 VPW), 1.5% accounts for +/- 156 bits per second drift. At 41.6K, this increases to +/- 624 bits per second. Sizable difference.

Often, replacing the PCM resolves the timing issues since the problem is usually isolated to a specific PCM.

Hope this helps.