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Discussion Starter · #1 ·
Hi all, I have a 2008 PT cruiser (base model automatic) that the battery light keeps coming on. battery reads 12.9 resting (off) and 15.7 @ 2000 R.P.M. Sometimes the light wont come on for 10 miles then boom. On it is. Any ideas as to where to start with this problem?
 

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Welcome to Allpar. Any stored PCM fault codes like P2504?:
P2504 Charging System Voltage High (at https://www.engine-codes.com/p2504.html )

The Powertrain Control Module (PCM) monitors critical input and output circuits of the charging system, making sure they are operational. A Diagnostic Trouble Code (DTC) is assigned to each input and output circuit monitored by the OBD system. Some circuits are checked continuously and some are checked only under certain conditions.

Inspect the battery posts and terminals, alternator connections and any intermediate connectors for poor/loose connections, corrosion or other defects visually. Overcharging can damage the battery and other components, so you don't want to drive it like this.
 

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According to that source link that I C provided, P2504 Charging System Voltage High, there are only a few possibilities: faulty generator, short to ground or power in the generator 2 wire harness, poor electrical connections in the same, or PCM charging control issues. See attached image. I believe this is a correct wiring diagram for a 2008 PT Cruiser. Verify that wiring to the generator matches this diagram.

Generator Wiring Detail.gif

Check fusible link for continuity. Check 2 wire harness for shorts to ground, power, each other at the electrical connector and along its length. If you find no issues with the wiring harness have the alternator checked. It could have an internal short to ground or other problem.
 

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Discussion Starter · #4 ·
Hey Imperial and Allan. Thanks for your response. There are no error codes. This morning i started the car and the battery light stayed oni ran it for like 10 minutes and then i just shut her down and waited a few minutes started her up again and no battery light. I made it all the way to work with no battery light so its kinda intermittent i would say. I will go through any way and check what you guys said tonight when i get home.
 

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Check for intermittent or damaged ground connections.
 
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Or one of the negative battery cables.
 

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The battery has to be considered a part of the charging circuit. It acts as an accumulator and can be a load for the charging system.
If this overcharging is intermittent in nature, then it does sound more like a poor connection than a failed component.
Look over the underhood electrical wiring and terminals carefully. Start with the battery. I would pull the terminals right off the posts and look for hard scale build-up between them. Don't forget to reset your clock.
Check for corrosion. Check the terminals at the rear of the alternator.
Are you near the salt water coast? Has the car ever been through a flood?
 

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I know I sound like a busted record on these PT Cruisers, but you really need to check the grounds on the inside of the driver side fender. Since they're right by the battery, these connectors often get the dreaded green corrosion and either break or lose connection. You'll need to remove the air filter housing in order to see them.
 

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A failed brush in the alternator can cause this. Here's how...
Ignition enters one brush passes through the rotor bobbin, then out the 2nd brush then it goes to to voltage regulator.

If the second brush fails and allows brush, brush lead or spring to touch negative it will full field the alternator. It's a possibility that needs to be proven as bring not the cause.
 

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I've read that the battery temperature sensor can cause the battery light to come on. Anyone have any experience with that? My dad's 2001 PT Cruiser is having the occasional battery light and a "ding" sound. I'm not close by enough to check it out at the moment. Trying to figure out what it could be before I get up there again. It seems to run fine otherwise.
 

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A good OBD scan tool will be able to show cleared codes. The battery voltage of 12.9v is high, should not be over 12.6 and more like 12.4-12.6 so your meter is reading high. Regardless the running voltage is high as it should be around 14.0 (13.8 to 14.2). I agree with checking the wiring and grounds. The voltage regulator is in the PCM and is extremely reliable and typically either works or doesn't. High resistance in the charging circuit would cause the voltage regulator to charge high as the voltage regulator would not be seeing the full output from the alternator.
 
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