Gatzer

Doing a search, I found and read the following threads.

http://forums.corvetteforum.com/show...ighlight=P1637
http://forums.corvetteforum.com/show...ighlight=P1637
http://forums.corvetteforum.com/show...ighlight=P1637
http://forums.corvetteforum.com/show....php?t=1372316
http://forums.corvetteforum.com/showthread.php?t=944784

I'm only getting the code P1637 after the car is at operating temp. Upon initial start, the voltage is fine, between 14.0 - 14.2. Once the car gets up to operating temp, it gradually drops down into the mid 13's and stays there. Then I start getting the code. It doesn't matter if I'm driving down the road, or parked at idle. Occasionally, I'll see high 12's. I have done the following things and still get the code, along with having voltage issues.

- Replaced a 6 month old Optima battery with a new one. Both checked out fine.
- Had the Alternator tested by 2 different shops. Checked out fine, but had new brushes put in anyway.
- Installed a new Ignition Switch.
- Pulled off the starter. Cleaned and re tightened all connections.
- Checked and cleaned the cars ground connections.

Does anyone have any other ideas or know the cure? This has gradually been getting worse over the last 6 months. I can clear the code, but it comes back every time. Sometimes in minutes, sometimes right away. The only code I get is Service Vehicle Soon / P1637. I don't get System Charging Fault on the DIC.

I have an '04 Zo6 w/ less then 9k miles on it, and a 14 volt, 145 amp alternator, thanks.

Y2Kvert4me

So you don't have the stock alternator on the car?

Gatzer

Still the stock alternator, just had new brushes put in it for the heck of it.
It didn't make a difference.

Y2Kvert4me

It's gonna be tough to diagnose this without a Tech-2 scanner.

That first link you posted contains all the info about this code, why it occurs, and steps to troubleshoot it. http://www.gearchatter.com/viewtopic10125.php - that is straight out of the factory service manual. This one is typically out of the realm for the DIY home troubleshooter.

The alternator may test fine as far as spinning it and producing current, but something in the control circuit isn't functioning as it should.

Is your 04 not still under warranty?

Gatzer

Ugh, if I took it to a dealer and they opened the hood. it wouldn't be for long.

Thanks for you help, man.

roushraven

When you figure this out let me know because I am having the exact problem in my H/C '03 Z with 32k miles. I replaced the battery but that didn't help since the problem code still returns. Unlike you, however; I do occasionally (3-4 times in the last 4 months) get the System Charging Fault. My car runs well and the performance has not been affected.

-RR

Mike Mercury

but was it testesd at a hot (underhood type) temperature ???

the bench test may not be simulating the environment that the alternator is actually seeing. The windings may start shorting out under hot temps, but the short clears once it cools down. Alternators can get very hot under the hood. So hot that you wouldn't want to touch it just after engine shut down from a moderate drive.

As with any intermittant failure, sometimes all you can do is repair via the "process of elimination". Replace the alt and see if the problem changes any.

.

Gatzer

Went out in the car last night. On the way to meeting some friends, I got the code and the voltage started moving around between 12.8 and 13.8. But, on the drive home, the exact same distance, voltage held in the high 13's and no codes.

I'm ordering a new alternator tomorrow anyway. What the heck, it's only $400.

Sick Z06

I'd have to say that replaceing the alternator completely should have been done before the brushes. When you get a "hot soak" problem such as this I would instantly suspect bad wiring, and or an internal issue with the alternator. However since it was not an RPM related voltage issue, the brushes would not have been my first suspect. Rather the internal diode setup instead. Once those puppies get hot, if they have an internal problem they will LEAK voltage and not put out correctly.

Let us know it replaceing the alt. takes care of it. If it doesn't there's one other tip I have for you.

Disconnect the battery, and measure OHMs from the alt output wire to the + battery cable end. Should be extremely low. Reconnect, drive the car up to operating temp.. Return home and do the same test. The wire if in good condition should NOT change much at all OHM wise.

Mike Mercury

uuuuughhhh !!!

I was looking for those words ("hot soak" or "heat soak") and couldn't -for the life of me- get them out...

Sick Z06

happens to the best of us mike.

Gatzer

Well, the only thing that either electrical shop could do was change the brushes. There aren't any other parts available for the late '03 and '04 alternators. If you have something wrong with one, you either have to buy a new one, or take the whole car in for a warranty claim. Also, these aren't Delco / Delphi alternators, and there aren't any aftermarket ones available either, or so I'm being told. They're Valeo's and made in Mexico. At $400 a pop, I wanted to rule out all the other little things first.

Thanks for the tip on the wiring. I've already checked / inspected it throughout the main harness from the alternator to the starter to the battery. It's fine with no voltage variation and reads the same, engine hot or cold. The only things left that it could be is the alternator or PCM.

And yes, my under the hood temps get a little hot thanks to the F1R.