Alternator not charging?

Measure the voltages on the three wires on the alternator. The large output wire should have battery voltage on it of 12.6 volts with the engine stopped, and it should go up to 13.75 to 14.75 with it running. The voltages on the two small terminals have to be taken with the engine running. Remember that these newer trucks see the battery is charged and allow the alternator to "let off" on the charge to save gas and not to overheat the battery. Here is the alternator wiring diagrams so you can see how the system works. Check out the diagrams (Below). Let us know what happens and please upload pictures or videos of the problem.

Nope. Building the voltage regulator into the generator, like GM and Ford do, insures you have to buy more than what must be replaced. Chrysler never did that. The voltage regulator is inside the Engine Computer where it can adjust charging voltage or turn the alternator off based on air temperature, coolant temperature, wide-open-throttle, and anything else the computer knows. This makes their alternators real simple and the circuit is easy to test.

You gotta be more specific so I can figure out what's working and what isn't. What are you turning on and what stays at 12.1 volts? What are the three voltages on the alternator wires when the engine is running?

The two small wires won't have voltage until the engine is running. I need to know what you find on them when the engine is running. In particular, the brown / gray wire has to have something, but I haven't worked on this new system so I don't know if it's a voltage or a square wave pulse. If you find 0 volts with a digital voltmeter, or if the reading is bouncing around, check it with a test light. According to what I've been reading, this is the only control wire so you'll rarely find full battery voltage on it, if ever. A digital voltmeter will get confused with a pulsing square wave, but a test light will smooth it out and give you a better indication. I think the light should be dimmer than when it's connected to the battery.

Hello,

What do you mean you have 12V to alternator? The alternator is what charges the battery. In the diagrams down below I have included a wiring diagram of your vehicle's charging system for reference purposes. Here are a couple of links for you to go to:

https://www.2carpros.com/articles/how-to-check-a-car-alternator
https://www.2carpros.com/articles/car-battery-load-test

Please go through these guides and get back to us with what you are able to find out.

Thanks,
Alex
2CarPros

I am not sure I understand where you are finding the 3 volt drop. Is this on the wiring or are you saying you are finding this internal to the PCM?

The reason is, this generator sense circuit is what the generator sends back to the PCM so the PCM can compare that to the B+ it is getting from the TIPM. When they are not the same it commands the regulator to increase the voltage.

Sounds like the PCM (regulator which is internal to the PCM) is not able to command the voltage to increase.

Let me know if I am not understanding where you are checking this voltage. However, the fact that you have 9 volts on the sense circuit is where your issue is.

If all your B+ are 9 volts it sounds like you may have a ground issue. You can check and clean the grounds but to confirm this, you can just back probe the grounds with a safety pin and run them to the closest stud on the engine block just to test this. It will take the easiest path to ground so if there is a ground issue, this will clear it up and then you will be able to track down the issue.

I think you nailed it. Let us know what happens after you get the PCM in there. Thanks for the update.

The most common alternator failure is worn internal brushes, and those always start out as an intermittent no-charge problem that gets progressively worse over weeks and months. The brush assembly can be replaced for around $12.00. The next most likely suspect is a break in the field wire between the Engine Computer and the alternator. These can be found with voltage tests, but to be valid for diagnosing this, those readings have to be taken while the problem is occurring.

The heater fan motor won't have any effect on this when it's turned off, and from what you described, the best suspect is worn brushes in that motor. Hitting it and it starts running is the big clue there. I'm working with another fellow for the same problem right now. His looks like it's going to be related to overheated connector terminals on the back of the HVAC controller, but his symptoms are a little different too.

Engine idle speed can be affected by an intermittent charging system. When it cuts out, system voltage drops, and that is the voltage applied to the injectors. With less voltage across them when the computer pulses them open, it will take a little longer for their valves to be pulled open, so you'll get less gas. If this condition lasts long enough, the computer will pulse the automatic idle speed motor to get idle speed back up, and you'll see short-term fuel trim numbers increase to get the volume of fuel back up to where it should be.

If you can catch the charging problem acting up, measure the voltages on the two smaller terminals on the back of the alternator and tell me what you find. These must be taken with the engine running. It would also be helpful if you can see what those voltages are when the system is charging normally.