Replace two time alternator both brand new but voltage read 12.2.

I remember a friend of mine had a similar problem with oil pressure reading. He had all this parts replaced a few thousand(replaced ecm). Come to find out a bad wire was the problem. All was start with the simple things first the wiring. If there is a break in the wiring or bad connection along the wiring you are not going to get a good reading. All the best to finding that electrical headache.

 

Well, not for nothing, at least you have new parts, even though it may be something as simple as a bad ground. Does the alternator get hot? Also, I wouldn't trust a dash gauge entirely, and sometimes, a good rap on the gauge gets results. Electrical gremlins are the #1 problem of older trucks. Start with a new ground to the engine and/or cab.

 

Hmm. Might be a ground problem, check main grounds, especially engine to frame.
Cascadia does have a voltage sense fuse, it’s only a 5 amp, but usually if it goes the alternator puts out too high volts, like 14.5-14.8 v.

 

Important to check voltage with a digital multi-meter of each battery when truck is running. I ran into into a bad positive inter-connect battery cable on a Peterbilt one time. The ECM was getting its power from that battery but it was not being charged because one of the positive cable tying the batteries together was bad in a spot but physical appearances of cable would not suggest that.

Another instance was a Cascadia that was low voltage message on dash. Diagnosing tech indicated voltage loss on positive cable to SAM chassis or near it from battery #2 & needed replaced. He already removed it when I was given job. Made the cable as specified and installed Fault was still there and then I got to some further diagnostics. Measuring the voltage of each battery I found #1(outer front) #3 & #4 that same.. However, battery #2(inner front) was way less. Then measured voltage drop between positive terminals and it was almost nothing. Across negative terminals of #1, #3 & #4 was almost nothing but between battery #1 & #2 it was about two volts where the interconnect cable was missing. Battery #2 is where all there power is feeding for the chassis and cab. It show be the same voltage as all the other batteries if the cables are good.
Danny50 if you need further help post the last six digits of your VIN and then we can get you more accurate information.

 

The alternator remote sense fuse is "Fuse D" a 5 amp fuse in the Powernet Distribution Box (PNDB)

Alternator power and ground cables run along lower right side of engine to the starter. Inspect to make sure everything is connected and tight. Then I would with truck running measure voltage at alternator, at starter, at each battery. Also, you have have Mega Fuse Junction Block (MFJB) and Mega Ground Junction Block (MGJB) feeding power and ground to the feeding everything but starter through them. You could check for bad fuse. Here is the schematic for that. Hope this can help. Please post what your find or if your are able to get problem solved.

 

Danny50 I did a little further searching in service information found some charging system diagnostics steps.
The formal steps will help focus your troubleshooting and hopefully get to the cause of problem.