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2009 jeep grand cherokee charging system failure


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Atlas42
New User

Sep 30, 2024, 4:25 AM

Post #1 of 2 (536 views)
2009 jeep grand cherokee charging system failure Sign In

2009 grand cherokee charging system failure
Customers states.... Battery light came on halfway through a 5 hour drive. My mother is driving and tells me it lit up I knew it'd be dead soon so I told her to stop at a service area and i grab my voltmeter i luckily had to diagnose. We are at 10v and losing slowly. System charges to 12.4-12.6 when no ignition engaged. Turn key to ignition and drop voltage drastically. Losing .1 per second when cranked and running. When off right back up to 12.4. It's 2 am and I am guessing a bad battery and alt might be it so just plan to Uber to a store to grab new ones. Do some checking on components and fuses in the mean time.

Components checked: Terminal connections and post cleaned

All engine compartment fuses and relays checked for continuity. Voltage good across relay pins

Checked accessible grounds in engine compartment and underneath the vehicle

Checked voltage from alternator to positive terminal. Voltage is almost equal which makes me assume alt isn't charging. Voltage was around 12.4 I can't remember exactly but it wasn't 13-14v.

Checked voltage drop from chassis/ground to negative terminal. Very low drop. 8mv

Replaced battery due to old one has now drained multiple times and I want to elimate the possibility.

Issue persists. Preform ripple test with new components get "failed test replace alternator"

on to the alternator. Autozone tells me the SoC is too low to test system and is at 28 percent SoC with the brand new battery. I dont have my scanner with me and the only one at my mothers is my obdeleven so i grab a cheap one which tells me no codes. Great. Buy an alternator if it doesnt work ill just return it. Swap it out in their lot.

Replaced. Issue seemingly fixed and begin driving back to my mothers. An hour in the battery light comes on so I just continue driving the remaining 40 minutes because I'm not sitting in a parking lot again. Tried to maintain high rpm to hopefully keep alt charging. Make it to my mother's house and voltage just plummets after pulling in.

During the install of alt I inspected the tensioner and serpentine maybe the serpentine is overcharging system being too tight. No squeak; belt tight; pulley spins with resistance; no play side to side.

Belt has some signs of wear and minor shine to it but the lack of noise and overall lack of symptoms i doubt its the issue.

Inspect the power/ground cables backside of alternator and the clip doesn't seat all the way and pulls off easily. Try it with the connection temporarily held 100 percent on still persists.

Voltage regulator i belive is in the alternator hear but might be wrong could be backside of engine like some vehicles I haven't pulled the schematic.

No parasitic drain system charges when ignition is not engaged

Things left to do that i can think of: Pull driveshaft and check starter wiring but the lack of drop in ground/chassis i don't see open wiring contacting and grounding out to something.

Pcm replacement

Voltage regulator

Visually inspect every wire/harness individually

Pull fuses and relays replace one by one until fault is reached.

Ignition switch


If anyone has some input id greatly appreciate it been working in the rain on this for days and I'm getting tired


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Sep 30, 2024, 7:09 AM

Post #2 of 2 (531 views)
Re: 2009 jeep grand cherokee charging system failure Sign In


Quote
Voltage regulator i belive is in the alternator hear but might be wrong could be backside of engine like some vehicles I haven't pulled the schematic.


The voltage regulator for all fuel injected Chrysler products is built into the PCM so you would likely need a bidirectional scan tool to be able to diagnose that.

Unless it's slipping the drive belt has nothing to do with the amount of charging.



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