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2005-2009 Mustang S197 Discussion & News

Odd charging issue

Old 3/9/19, 10:42 PM
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Odd charging issue

I'm putting the backstory on this in case anyone has seen anything that may tie these things together. I've been patient, understanding that a 10 year old car is going to have issues, but I'm now at the point where I seriously regret buying it.

I've got a 2008 GT, automatic, stock.

Jan 24, 2019, I bought the car from Carmax.

Feb 2, just over a week later, the check engine light comes on. It's code P0155, O2 sensor. I take it back to Carmax. They put an O2 sensor in it, claim it was a bad one and they needed a Ford OEM sensor, which still doesn't fix it, so they send it to the Ford dealership, who claims they put the wrong O2 sensor in it, which still doesn't fix the CEL. They conclude that the PCM needs to be replaced, and it takes them until March 1 to do all this diagnosis, approve the new PCM, and have Ford put it in the car. I pick up the car on March 1.

March 2, ONE DAY LATER, I'm driving home and the battery gauge (I'm guessing it's a volt meter) starts to drop, and a block from my house the gauge turns red since it hits bottom and odd lights are coming on in the gauges, the ABS light and traction control light, along with the battery light. The radio was off but came on and reset itself, and the CD changer started clicking. I turned off the headlights and pulled the parking brake while I was sitting at the red light, and that brought the gauge back up where it should be. I got home and checked the battery voltage with the car off, 11.5V. It sitll managed to start the car. With the car running, 11.0V. I charge the battery and on Monday morning, March 4, I take it back to Carmax. They replace the alternator and battery, and I picked it up yesterday, March 8.

Today, ONE DAY LATER, while getting on the highway, I gave it a good bit of throttle and the ABS and traction control lights came on in the gauges again. They turned back off when I let off the throttle. I noticed it continuing to do this, and found that anything over 2000 RPM would cause those lights to come on along with the battery light, and would peg the battery meter all the way to full. Later in the evening I was driving and it happened consistently over 2000 RPM, and if it stayed there for more than a few seconds, the interior lights would turn off, but my headlights would remain lit. Once the RPM dropped, the interior lights would come back on. The fog lights would also turn off when this happened, and the radio has reset itself again.

I've heard about the 2010 alternators being a better 3-phase design, but I'm not sure what got put into this car for a replacement alternator. I'm thinking it's the original spec single phase alternator, if I read other posts correctly as to how it came from the factory.

Any thoughts? Has anyone experienced stuff like this? I'm taking it back to the dealer on Monday morning.

Last edited by Blue Roads; 3/10/19 at 10:11 PM. Reason: Add vehicle details
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Old 3/10/19, 04:38 AM
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Hi Blue Roads. It would also be helpful to know what model year and engine you have. I am guessing an '09 based upon your post info.

There's a couple of possibilities to look into. One is the infamous SJB (secondary junction box). It sits behind the front passenger kick panel. Pull the panel and look the SJB over for corrosion, as though it has gotten wet several times.This can be the root cause of numerous electrical gremlins on the S197's.

It happens sometimes because drain holes for the passenger side cowl area get plugged by leaves or debris. You can check this by opening up the well where the cabin air filter lives. Wet in there? Drain holes plugged? I'd get suspicious about the health of the SJB. When that space can't drain properly, the overflow will frequently find another escape; often over the SJB.

Less likely, but maybe contributing to it all, is that a few (not all) of the 2005-2009 models have had chronic issues with batteries/alternators. I replaced the battery seven times over about ten years. Ford changed the alternator they were using in the 2010 models. They fit and work fine in the 2005-2009 model years, and that is usually the solution.

But I would look hard at the SJB is a possible root cause for your wide variety of electrical issues. If that is not it, then I'm stumped. Hopefully someone else will also chime in.

Last edited by Paris MkVI; 3/10/19 at 04:42 AM. Reason: typo
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Old 3/10/19, 07:13 AM
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Originally Posted by Paris MkVI View Post
Hi Blue Roads. It would also be helpful to know what model year and engine you have. I am guessing an '09 based upon your post info.
Oops, that would definitely help. It was late and I flaked out on that. It's a 2008 GT 4.6.

Thanks for the info, I'll check the SJB. I don't know if I can talk them into putting a 2010-spec alternator on it. What does an OEM unit cost, approximately?
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Old 3/10/19, 12:54 PM
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I checked the well by the cabin air filter and it's dry. The drain didn't look plugged either. There was one small leaf in there. I didn't get a picture of the drain, just the area over by the filter. The SJB looks to be in really good shape from what I could see.




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Old 3/11/19, 10:26 AM
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Can you get the same symptoms just revving the engine to 2000 rpm at idle? If so have someone rev the engine and try wiggling all the wiring harnesses in the engine compartment to see if a loose connection is causing the issue. Would you know if this car has been in an accident? If so I would check that area for loose ground wire connections to body panels or frame mounts. There's a ground just over the left headlight for the abs. Also check the area carefully where they installed your new pcm. There's a couple of ground connections there. They may have forgot to install or tighten a wiring connector in that area.
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Old 3/11/19, 10:42 AM
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Originally Posted by Lime GT View Post
Can you get the same symptoms just revving the engine to 2000 rpm at idle? If so have someone rev the engine and try wiggling all the wiring harnesses in the engine compartment to see if a loose connection is causing the issue. Would you know if this car has been in an accident? If so I would check that area for loose ground wire connections to body panels or frame mounts. There's a ground just over the left headlight for the abs. Also check the area carefully where they installed your new pcm. There's a couple of ground connections there. They may have forgot to install or tighten a wiring connector in that area.
Yes, it happens even if I rev it over 2000 in neutral. I'll try those things, thanks for the info!
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Old 3/11/19, 10:43 AM
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One up side to this is that I put a new cabin air filter in it!
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Old 3/11/19, 02:54 PM
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I agree, your SJB looks good, so that hopefully is not the cause.
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Old 3/11/19, 03:46 PM
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Originally Posted by Paris MkVI View Post
I agree, your SJB looks good, so that hopefully is not the cause.
Thanks. You are my inspiration to be patient and get this worked out. I'll keep looking at the cars in your signature and think of how much I'll enjoy having this car in the years to come once they get it fixed. The dealer is fixing it all under warranty and I let them know about the 2010-spec alternators so let's hope they figure it out soon.
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Old 3/14/19, 07:13 PM
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I suspect it's just a bad alternator. I've experienced those same symptoms when an alternator was going bad.

If you have a way to watch the voltage live while you're driving, I'd bet you see a large spike in the voltage after you pass that RPM.

I posted all the symptoms and info on this, but it was many years ago and I don't even remember what thread it was in.

But the basic symptoms are... Voltage spikes, ABS and traction control lights up, electronics start shutting off. Car stays running though.
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Old 3/14/19, 09:05 PM
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Originally Posted by stupidgenius36 View Post
I suspect it's just a bad alternator. I've experienced those same symptoms when an alternator was going bad.

If you have a way to watch the voltage live while you're driving, I'd bet you see a large spike in the voltage after you pass that RPM.

I posted all the symptoms and info on this, but it was many years ago and I don't even remember what thread it was in.

But the basic symptoms are... Voltage spikes, ABS and traction control lights up, electronics start shutting off. Car stays running though.

Thanks Genius, I got it back Wednesday with a new alternator in it and it's working properly now. It's reassuring to know you saw the same symptoms and it was a bad alternator.

Last edited by Blue Roads; 3/15/19 at 08:13 AM.
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Old 3/27/19, 05:56 PM
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2 weeks now and it's still running great. Been driving it pretty easy most of the time, averaging 21 mpg.
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Old 3/27/19, 10:40 PM
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Howdy. Missed this thread, good advice all up in it. These cars have some issues with the battery/charger, but I found the following to be good stuff to help prevent recurrence, so far anyway. I'd just recommend this as a 'closing argument':

This post was four years ago. I can tell you that was a couple of years easily after doing what I described, so it's been something like 6 years and no issues since. Terminals still look as good as when I did them (well... they're dirty from dirt, truth, but they're not corroded, which is the key here.)

Dielectric grease is not pretty, truth... but it works and that's the key. Any and all corrosion is going to screw up these car's electricals, it's just the way they are. Nip it in the bud. Oh, and in your case, with the new alternator and battery and such, you probably don't need to do all that in the post, but definitely the battery terminal washers and dielectric grease on them as described: bottom first, install terminal, slather the rest. Positive first, then negative. And if you can, do the alternator connections, they're just as important.

Hope that helps, glad you got the car sorted out!

Last edited by houtex; 3/27/19 at 10:45 PM.
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