Have Jeep Questions? Ask a Jeep Repair Expert for Answers
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What is the engine running voltage from the alternator at the battery when the problem is occurring?
The normal charge rate on a properly charging alternator should be 13.6 to 14.2 depending on the amount of load. Is your staying in this range?
Your charging rate is controlled by the PCM (computer) and will go up or down depending on load. Are you able to do some testing when the voltage drops if I send you you steps to do so?
All you will need a a volt meter. With out testing the circuit there is not way to know what is failing. The problem may very likely be with the PCM. Can you get your hands on a volt meter?
If in fact the PCM is the cause , no its not hard to change but before you change any parts you should do the testing.See the steps in the link below to test it as well as the factory wiring diagram for testing reference.https://dl.dropboxusercontent.com/u/104923897/Alternator%20Jeep%20Jan%2010.pdfhttps://dl.dropboxusercontent.com/u/104923897/Jeep%20wiring%20diagram%20Jan%2010.pdf
Yes Im here for a while yet today and all day tomorrow as well.
Okay . Im here if need be.
Yes, Ill be here.
Okay then you may want to wait this the problem is occurring to start your testing if in fact you actually have a problem.
Okay try that and let me know.
Its normal for the voltage to dope some when you put a load on the system like the blower motor, how far dose it drop?
Yes connect you volt meter to the battery and read the voltage while its dropping.
Okay connect you volt meter to the battery and let see if the voltage reading there match your gauge.
That is totally normal, as long as it dose not drop below 13.6 volts.
The fan speed is going to change normally as the voltage decreases and increases but if your voltage at the battery is not dropping below 13.6 volts with the engine running then you do not have a problem. If its dropping to 12.9 then take a ground wire with the engine running and probe the green wire on the alternator and see if the voltage come back up as it should . If it dose climb back up then your PCM is faulty.
Yes Im still here, did you ground the green wire with the engine running?
What I need you to do is with the alternator on the engine and running back probe the green wire at the alternator with a ground wire and see if the voltage starts to climb. Did you do that?
Thats is not what I need you to do. I need you to ground this wire. Jump a wire from the negative battery post and probe the green wire with the ground.
With this wire ground the alternator should full field and charge at the full rate. If it dose then the problem is with your PCM. Let get it grounded with the engine running and see if the voltage climbs up as it should.
No problem, lets try this and let me know the results.
Let me know when you readyl
You need to probe and ground the dark green wire at the alternator. It is the only dark green wire.
That dose point towards a problem with the PCM , for some reason its not allowing the computer to keep up with the load on the charging system. Your very welcome and thank you as well.