Super common to see alternators go out on F136 engines.
Now here is a quick list of how they go bad, usually every 50-70k miles heat is the major cause (as they're encapsulated in the plastic intake with zero air flow)
Mostly a rectifier that's gone toast, that said the symptoms are varied
- Not loading (aka alternator light constant) easy
- Loading only at idle 12.5 ish and whilst driving 12-12.5 < no light and a lot of odd issues and flat batteries
- Loading only at idle not at 2000-3000 rpm, (or 11.9 ish) often no light and F1 issues (highway, F1 pump will start suffering)
- Rectifier toast overcharging 14+ volts I've seen them blow dashboards with 18v spikes
Cars eating batteries is one sign, odd gremlins a other.
How we test it is not only checking the battery in the back, that in the second one of the list can be misleading, for the other cases:
Using a diagnostic tool whilst running under-load, check: (I have the customer drive while i check with the laptop, but you could do it differently)
BCM (dash-fuse box and body module) OR NQS that's the cluster
NCM (ecu in footwell)
Trunk canbus node OR NCR/TCU (f1 only) which is directly above the battery
So from alternator towards battery, you will notice that each will have a different voltage, the battery being a buffer.
Bad alternator will show up away from the battery dropping that ecu or group below 12 some times hitting 11 (be sure to use lights, defogger etc as test)
Bearings:
Actually a lot less common, the bearings that do fail often at same interval would be AC compressor clutch or the main-bearing of the pump.
Super common again 50-70k miles.
