How often do PCM computers fail?

[wanderingturtl]

How often do PCM computers fail? I think I've found 2 bad ones out of 4 buses so far. We have been troubleshooting some buses that I bought on auction. One of them I confirmed had a bad computer, and another I suspect the same things. Are computer failures common or likely?



On the one that was confirmed, it kept giving about 7 random trouble codes, that would immediately return upon resetting. I exchanged the computer and the problem went away. Also, when trying to remove the bad computer, one of the bolt just turned forever. I would up having to drill off the bolt head to remove the connectors. I suspect that it was overtightened at some point. The round covers were already off of the computer, so I know that someone had been there before.



Now on the one that I suspect has a bad computer as well, it gives 3 fault codes, which immediately return upon resetting. Also, when cranking, there is no RPM detected. I have verified that the CPS is good. So, I think that it could be a wiring issue, or perhaps more likely a bad computer? And, when trying to remove this computer, there was the same problem of the bolts spinning but not coming loose.