2012 Jeep Liberty Limited 3.7L Not charging new batt/alternator HELP

Hello, I am working on a 2012 Jeep Liberty Limited 3.7L that was brought to me due to not charging. The customer advised me that the vehicle was not cranking over so he thought it was the battery that had gone bad. The customer put a new battery and it did not fix the problem. The customer then took the vehicle over to a shop where a brand new alternator was put in and it still did not fix the problem.

The first thing I did was hook up my snap on solus edge scan tool and run a code scan. I got a bunch of codes in reference to a low voltage from several of the body modules. I then opened up the Mitchell repair manual and followed the prcedures for the DTC P0562. Everything seemed to be okay. I then believed that the PCM was bad because it was not signaling the alternator to engage.

I wanted to be sure before telling the customer to replace a 400 dollar part so I continued to check the wiring. I found something that was odd. The batt sense wire that comes off the back of the alternator is supposed to tell the computer how much voltage the battery has. When a specific voltage is met, the the computer then sends a signal to the alternator to activate it (PWM). When I hooked up my volt meter to battery ground and battery positive I got a reading of 12.5 volts. I then moved my positive lead to the batt sense wire behind the alternator and got a reading of around 9.5 volts. This seemed odd because the battery was fully charged. This reading was with the key on. I then noticed that when I would disconnect the batt negative and reconnect it the voltage would then read 12.5 volts. As soon as I would turn the key forward, the PCM it would then read the 9.5. There was clearly some type of voltage drop. I started to check the PCM connector where the batt sense is connected to and the other wires on the connector. I found that the can bus (-) and can bus (+) had continuity with each other. I also noticed that the shielding was browned as if they were or had gotten hot. No fuses are burned on the vehicle. and the vehicle turns on fine. I tried tracing these 2 wires down, but had no luck. IM STUCK ANY IDEAS? Am I doing something wrong?

I also noticed that the cluster is not giving me a battery warning light. I also have noticed that when I disconnected the TIPM connector where the Can Bus (-)and (+) run to, the continuity tester light turns off. HELP

Pretty sure that is normal on the sense wire, for it to be 3 volts less than battery voltage with the key on. What voltage do you have on the field wire? And did you check the wire between the battery and alternator?

I think I have a good article on Chrysler charging systems on my computer at work. I will post it up tomorrow

The filed wire has ground no voltage

The filed wire has ground no voltage

I place my test light on the field wire and and battery negative and it did not light. I then placed the test light terminal on the positive side and it lit up. The why I say it has ground

and thank you so much for the response Bruce Oliver I really need as much help as I can get. BTW what do you thing about those CAN BUS wires? is it normal for them to have continuity?

Sounds like a bad PCM, but you need to check the field wire and make sure it's not shorted to ground somewhere

gonzalezaamg28 wrote: and thank you so much for the response Bruce Oliver I really need as much help as I can get. BTW what do you thing about those CAN BUS wires? is it normal for them to have continuity?

Yes that can be normal. What is the actual ohm reading? Are you checking at the DLC? Chryslers are different from a lot of cars, the CAN circuit to theDLC is a separate circuit from the com wires between modules. The car starts and runs, if there was a problem with the CAN wires it would set codes and/or not communicate with your scantool

Here's the article. Click the top link for Chrysler's. It is a PDF file. It explains dual field wire systems and single fields. Page 2 of the article has testing procedures and explains why the sense wire shows 9.5 volts when the key is on.

www.remyautomotive.com/resource/Technical-Bulletins

got it. i didnt take an ohm reading. Im still new to the auto electric world and learning how the system works. I did notice they looked like they had heat stress due to the outer shielding being browned. I did do a voltage drop test on the can bus (-) and got a reading of 2.50 volts. I then started to disconnect one connector, but it didnt change anything thanks in advance.

Do you think the internal EVR went bad in the PCM?

Yes for sure I will recheck it tomorrow. by any chance would you happen to have a good wiring diagram of that wire and what else its connected to if any. On my mitchell diagram It looks like its only connected to the pcm. I did jump this wire and got nothing. Another thing, if there is a short to ground will the PCM circuit go into a limp mode or something?

you should have key on engine off test where you can turn the alternator field driver circuit on. what is the commanded duty cycle?? do you have 12 volts at the big cable?

I do have 12 volts on the big cable. I also hooked up my scan tool and tried to activate the field circuit and I only got 0.55 volts on the filed wire.

Okay guys I checked the gen wire and it definitely has a short to ground. I then checked for continuity between the computer casing and the gen field pin and it had continuity ! Is this normal?

OKAY GUYS SO I FIXED THE CHARGING ISSUE ON THE JEEP LIBERTY. THE PROBLEM WAS A BAD PCM. I FOUND THIS BY CHECKING THE FIELD WIRE FOR A SHORT TO GROUND, WHICH IT DID HAVE. I THEN DISCONNECTED ALL THE CONNECTORS FROM THE PCM AND REMOVED THE PCM. I THEN CHECKED FOR RESISTANCE BETWEEN THE PIN 19 (FIELD WIRE PIN) AND FOUND THAT THE PCM WAS SHORTING ITSELF TO GROUND. I PUT A NEW PCM AND ITS NOW WORKING. THANKS FOR ALL THE HELP GUYS.

Nice fix. Is there any suspicion that the first alternator may have damaged the PCM?

Bruce - Love that Remy page that you posted! :woohoo: I'm adding that to the service info sticky.

I’m not sure on the old alternator or batt they were both changed by another mechanic prior to me getting the vehicle. I never got to check them. Customer brought me the car because the batt and alternator swaps didn’t fix the problem.

Tyler wrote: Nice fix. Is there any suspicion that the first alternator may have damaged the PCM?

Bruce - Love that Remy page that you posted! :woohoo: I'm adding that to the service info sticky.

There is some great info in their bulletins.