jdvann

2001 Coupe M6
I have these Codes P1637/P1638 H and Charge System Fault on start up.
I also have B0432 HC
battery tested today on multi-meter
Cold- 12.3v
Alt back 12.3v
DIC- 12.1v

Start a cold engine and receive above mentioned errors.
Batt Voltage 11.7v
Alt back 11.8v
DIC-11.5v

Rev engine to about 2k RPM and volts rise and hold steady at;
Alt-14.8v
Batt- 14.7v
DIC- 14.4v
Battery load test good
Car sat for 15 minutes while I took the batt out and hooked to tester in Oreillys
Replaced batt, got Charge System fault on start but volts rose quickly to 14.4v on DIC
P1638 H was only code at this point.
Got home and tested battery with mult mtr and was 12.7v.
Let car sit for 5 min, started up and no faults and P1638 H was only code present.
Looking for some help...I got this error last week and would not go away. I then replaced alternator and this is where I am at today.

Thanks in advance...Jim

dadaroo

P1638 can get thrown when trying to charge a low voltage battery. New batteries are not always fully charged even if the surface voltage may read as good..

What is the idle charging voltage with the new battery?

Delete the code and see if it comes back.


Mr. Sam

jdvann

Once the voltage rises after throttle Rev and goes back to normal idle rpm the voltage remains at 14.4v. Measured at the battery. The battery is a 1 year old 800cca ac Delco.

jdvann

I just got home and checked my batt, the resting voltage right now is 12.57v. Should I throw a booster on it to simulate a better charged battery and try to start?

BigGun

If it won't start with 12.57 volts you have another problem. Did you clear the code to see if it comes back?

jdvann

It starts right up. Just get Charge system Fault on a cold start. At idle after start it sits at 11.8-12v, then I Rev engine and let off and the volts rise to 14.4v and will stay their at idle. I can clear the codes, drive for an hour, no codes. Will start without issue after that until it cools down and then the same problem/codes occur once it cools down.

73Corvette

Are you SURE you got the right alternator?

RedRiderZR1

If battery checks out and alternator is good you might want to check out your ignition switch contacts. Common C5 problem. Mine were pretty bad and had weird electrical issues. Cleaned the contacts on the switch and all problems went away. Your issue may be caused by bad contacts on the switch.

jdvann

I guess I am not sure now...I had a charge fault error and I was only getting 11.5v. to the Battery from the alternator. So i replaced it....with the only compatible alternator Oreilly's auto parts sales according to them. Just now I was reading a thread about High Output alternators https://www.corvetteforum.com/forums...lternator.html and the symptoms I have now mirror the ones with the Billet tech in the thread i.e. Get the RPM's up to 2k and the alternator excites and stays on, but It causes the CSF before you can get it to excite. But once it is working it stays working...until you do a engine restart.

73Corvette

Here is some homework...

https://www.corvetteforum.com/forums...-to-share.html

Bill Curlee

The connection between the BATTERY POS Terminal and the ALT BATT Terminal goes through the main connection on the Starter Solenoid terminal. If,,, its dirty, corroded, loose ect.. It will give you weird charge system issues. Check those connections

HERE IS YOUR CHARGING SYS SCHEMATICA;



Also make sure that the fuseable links are in proper working order.

BC

Bill Curlee

jdvann

Ok...I believe my connections are solid at the starter since I just had them off this weekend and wire brushed them until they were shiny on both sides and reinstalled. One of the most confusing issues I have is now that the car has warmed up(i just went for a ride) it jumps right to 14.4 on start with no CSF.

To recap this is where I am today...

1. Original issue...Had CSF and codes P1637 and 1638 with alt and batt voltage of less than 12v.

2. Went and got replacement alt from parts store installed.

3. Still had no alt voltage being delivered.

4. Did some research (should have done this first) and wiggled starter wires and power from alt would come and go.

5. So tightened starter wires...

6. That's when I started getting good voltage from the alt, but only once I did an initial rev of the engine(new alt already installed at this point).

7. So double checked my starter wires for tightness and broke starter solenoid...

8. New starter installed thus the "shiny wire" connections as mentioned above.

9 . Now I start cold engine and get CSF with the original codes.

10. Rev engine above 2k and Alternator energizes and remains steady at 14.4v, I can clear codes and they won't return after driving for quite awhile with several stops just to restart and test.

11. Once I park car and let it cool down the issue starts all over at # 9 and 10 above.

Bill, how do i test the fusible links?

Thanks in advance for taking time to read and assist with my most likely self inflicted wound.

dadaroo

I am going to PM you with my number so we can discuss. Much better communication that way.


Mr. Sam

73Corvette

Sam I totally get why it's SO much better to discuss this with the OP...
would you please fill in the blanks/summarize your conversations... problem... diagnosis... solutions... fix and post them...
If not just give me a call...lol
Thanks Steve

jdvann

OK so....

My first problem was I misdiagnosed the Alternator as bad and replaced it before proper diagnosis of all possibilities.

-It appears the initial and only original problem was loose wires at the starter, I had made my mistake already which led me to the next issue.

- I had replaced the alternator already with an O'reillys reman, and I was getting a new symptom at this point, had to rev above 2k RPM to excite the alternator

-I went through 3 alternators from Oreilly's all with the same symptom, had to rev above 2k.

-I then found a comment in a thread about High Output alternators by user CHOREO, where he had replaced his alternator 3 times with an Oreillys Reman before he got one from Auto Zone and all was well for him with the AZ Alternator. So I got an AZ alternator and BAM, all was good again...no Charge System Fault or PCM Codes. It appears Oreillys Alternators are not compatible with the C5 electronics as put forth by CHOREO and my experience with the Oreillys reman Alternators.

-Auto Zones Reman Alternators worked first time...

-The problem was wires were loose and I complicated thing by changing the Alternator, with what turned out to be a bad series of Alternators from Oreillys...
--AVOID Oreillys Reman Alternators!

-Thanks Sam (dadaroo) for getting me straight on diagnosis and thanks Bill Curlee for the wiring diagram! You guys are awesome!

73Corvette

were the Auto Zone and O'Reilly's alternators the SAME part number? What part numbers were they if different?
What was different about the AZ one that works?

dadaroo

Steve, What made me think it was a problem with "flashing the field" was that it would work when the RPMs were increased and it would work normally when hot. Increasing the RPMs when cold must have provided just enough induced voltage in the stator to get it going. When the alternator was hot, the residual magnetism in the rotor had not dropped off enough to cause an issue so it seemed to work normally when hot.

Alternators need to have the rotor produce a magnetic field which when rotating induces voltage and current in the stator (stationary). This is done in the C5 by the PCM introducing a 5 volt "flash" to the rotor to start things. If a stator has enough residual magnetism in it at startup then a "flash" is not needed. I surmised that it was a "flash" issue since when hot it worked normally.

I had him verify the PCM was providing 5 volts for the flash. Then I had him see if the alternator would work at the store if when cold and the "flash" voltage was not allowed to be used. When this was done the alternator would not work.

The O'Reilly alternator test stand must have been using a voltage higher than 5 volts to flash the field when it was cold. That made the O'Reilly alternators "seem" to be OK for the C5.


Mr. Sam

73Corvette

Thank you Sam... you took me out is some pretty deep water for an old Okie Oil Field hand... but I got the jest of what the issue was...
So the alternator from AZ and O'Reilly were actually (different alternators) or just the way the O'Reilly machine was testing it?

dadaroo

Different alternators. I would rule out some "old" windings or internal issue since he went thru more than one from O'Reilly.

I teach engineers how generators are designed and work in the nuclear industry so I understand them. The only difference is size and on a car you have to convert the AC to DC.

You would be surprised that in the power industry we keep them cool by circulating water in the stator and hydrogen gas around the space between the rotor and the stator.

Gotta do something to keep 'em cool when you are pumping out over 1000 Megawatts of power. We monitor those aspects VERY CLOSELY while we are operating. We don't let Homer Simpson around it.

Mr. Sam