I have a cat 3126 in a frieghtliner. It will charge sometimes and then drop off. When it charges it is 13.5v. When it does not it reads battery voltage. What should I check or replace first? Serial -8yl92142. Ar-197-1131. Core ar-173-1332. Oem-c01-00023-309. Famliy-Ycpxh0442hrk
If it typically charges when cold, and drops off when it gets warmed up a bit, then it gets a little harder to diagnose. Try to take it off when hot and not charging and get it tested at an auto electric rebuilder. The kid at the parts store will say it's fine and not test it long enough to cause it to shut down. Usually, the voltage regulator is on the alternator, so if the alternator has battery voltage at the small wire when it's not charging the same as it does when it is charging then the wiring is fine and the alternator is the problem.
I had a problem with broken corroded battery cable terminals. Replaced and everything worked. Hope it helps. 95 KW T600
I will check the voltage. But the cables are a bit corroded. I checked the voltage at the alternator big terminal and that read battery voltage when it was not charging. So I am not sure.
Mine was working one day and wasn't charging at all the next. Trying to start on one battery turning slow then the gauge would read 10 or so volts after I jumped it. 3 terminals replaced. Alternator circuit wasn't complete
Just so you know the battery voltage gauge will drop to battery voltage when the air intake heater is on. The heater takes more amperage than the alternator puts out. The heater usually cycles on for a while after start up. Make sure the heater is actually shutting off.
That sounds like the problem. Where is this heater?
Where the intake pipe goes into the head on the drivers side you will see a terminal with a large red wire going to it. Check for 12 volts at that terminal.