At the coast a few months ago, got a check engine light. Called Cummins tech support with the code, they translated to Cummins codes, told me the ECM was getting no signal from the intake manifold pressure sensor. Said this wasn't urgent although engine might be derated. Said it was probably dirty contacts or a loose wire. Coach was still drivable so did nothing until June when coach failed DEQ (pollution) inspection, blowing too much black smoke. At this point got some contact cleaner, cleaned the contacts, checked and now had two codes.
Took the coach in to Cummins NW in Portland, they replaced the intake manifold pressure sensor (boost sensor) and the barometric pressure sensor. The original sensors aren't used now, the new versions required different wiring to the ECM. Ten hours and $600+ later was out the door.
On the way home, pulling a steep hill, noticed boost pressure was up to 57. Called Cummins to see what they did, I've never seen 30 before on the gauge. I thought the new wiring was screwed up, they thought the waste gate could be stuck. Neither one, the new boost sensor defaults to reporting inches of mercury, not psi. Doubled the readings on the gauge. They changed something, not sure what, but now my gauge reads normally.
Wow that is something I have not yet experienced