P1637 and P1638. HELP please!
 

OK, I am pretty unhappy right now. My car has been down since November for various things like getting the lights tinted, interior stuff, 12 inches of snow, etc. I got my alternator case powdercoated and have had the battery unhooked for almost a month. I put the alternator back in early this week, and charged the battery with my on board trickle charger yesterday. Put the key in and cleared all the codes from the PCM (various door module communications, etc from the car being unplugged so long, and the battery drained once before I unhooked completely). Start it up and I get "service vehicle soon" on the DIC. Turn off, check codes PCM codes are back. P1637 and P1638Clear them, they come back immediately, even before I can start the car and I was seeing 11.4 volts on the DIC after starting. Take the battery to O'Reilly, it tests good. Take the alternator to O'Reilly, it tests good on diode, regulator, and rectifier - not to mention the guy that disassembled it for my powdercoater, tested it after he re-assembled it. Put it back together, same codes immediately. I am seeing 12.6 volts at the battery with the car off, 11.4 volts with the car running. My DIC has always been accurate on voltage, and I have always seen 14.3 or 14.4 with the engine running. I have verified theses number with a multimeter today just in case.

How in the hell can my car be working fine when I take it apart and not when I put it back together? No starting issues, now or ever. Obviously the system is not charging, what gives??

Jeremy

:lol: If that scenario never unfolded, this forum would only have half the threads it currently does.....

I don't think that's its a coincidence, that you are getting a P1637/38 code, and the alternator was completely apart. Start with the basics by checking the connector. If the wiring looks good, the alternator probably was damaged.

I had the same thought. I was sure it would test bad, but it did not??

Just an off the wall thought, but could the powdercoating be interfering with a good ground to the casing?

Oh crap. That could be it. Does the alternator ground through contact with the bracket????

Ahhh......yeah......

I am an idiot. I know this crap!! The powdercoater is not to blame. I am though...

I did not want to remove the bracket for powdercoating, so i painted it with black caliper paint.

Yeah, I painted the inner surfaces of the mounting points where the bracket meets the alternator.

Will fix tonight and report back with final embarrassing results.....

Well, not an easy fix so far. This is really long guys and I am sorry. Took it apart and cleaned all the bracket surfaces, put it back together and no difference - still codes, and still not charging. Cleaned it more, kept getting the codes. Got out my multimeter and had good ground with the + lead on the alternator terminal, and the black lead on the bracket, the mounting bolts, the inside of the front of the alternator case, block, chassis, etc. However only 1 to 8 volts if I touched the black lead to the any of the 3 bolts on back of the alternator that hold on the plastic part. Went to AutoZone, told them my problem, and they let me take a new one home to test. Hooked it up and had 12v everywhere I tested, including the 3 bolts on the plastic portion of the case. Cleared the codes from the PCM and they did not come back in a minute or so. I took the new one back for a refund. Now I knew I had a ground problem, but only to the back of the case. If you think about it, the case only contacts the bracket with the front of the 2 pieces, and the back is only grounded through the bolts that hold the case together. Apparently the powdercoat is not allowing that to happen. So I bought a 4 gauge ground strap, drilled a hole in the frame rail, and ran the cable to one of the large, unused, threaded holes on the back of the case.

Bingo! 12v anywhere I read it, including the 3 bolts through the plastic. Started it up, the 1637 code was there and 1 tcs code (?). It was charging at 14.3 volts. I cleared the codes, turned it off, and put the car on the charger, since I was only seeing 11.6 volts at the battery, with the engine not running.

So, why was the 1637 there again? I hope it is not tomorrow, cause I have a ton of time in this supposedly "fun" alternator powdercoating project, and I am out of ideas. Never had an alternator code before, why would I now, after getting good ground to the thing finally.

Any more ideas??

You seem to be looking for a smoking gun, but pretty much have found it. One thing you know for certain, a new alternator works fine...no codes, no problems. You know your alternator worked fine before it was taken apart for coating. Now it doesn't. You have made sure all the grounding points to the alternator and bracket interface are clean/bare metal. So what does that leave?

I agree, but I have always had good ground at the bracket, and the rotor inside the front of the case, and now I have good ground at any uncoated point on both halves of the case. So why would that code have shown up again? The alternator was completely bare of powdercoating under the plastic part when I took it off, I never removed the bracket, and there is good contact between bracket and alternator. Now I have added an extra ground.

Also, all I know about a new alternator is it did not throw the code with the car not started. I had to promise them not to use it, so they would take it back, as it was supposed to be un-returnable unless defective. I just used it to verify the way I should be able to see grounding with my meter at any point or bolt on the case, and verify the codes did not return immediatley with the key on, but not running, becasue they were returning immediately before.

My only options from here I see are have it torn down again (no big deal for me other than annoyance, and the possibility it may never be right again), replace the pigtail at the alternator (definitely seen better days, though no problems before), and check all the chassis grounds, cables etc (again - not a problem before, though some grounds are dirty up front, and I have not looked at the starter connections).

After that is is take it to the dealer for full diagnostics, live with it cause it is charging now at least, or replace altternator. I know I HATE seeing "Service Vehicle Soon" on the DIC!!!

Well, I am just lost now. The batery is fully charged to 12.6 volts, the code does not set when I turn the key on, but sets 5 seconds after I start it, yet the alternator charges at 14.5 volts. I feel like I am screwed because I either have to have the guy take it apart or just get a new one and end up with it not coated. I have good voltage and good ground, so I dont know. It is only setting P1637 now. Which wire is that, and why would that only set after start up but the alternator charge fine? What exactly (not the manual explanation) is P1637 related to that it was settign immediatley with the turn of the key before, and now only set after start up. Yet my extra ground obviously made a difference because P1638 went away and now the alternator works at least.

Also, the larger red wire of the 3 off the pigtail was spliced into by a past owner and a short wire was run from from the connector to the hot side of the alternator. Why would someone do that? In the midst of all of this, I undid that and spliced it back into the other end of the factory wiring? Should I put it back? I have looked at every alternator pick of a 2000 I can find, and dont see any with that wire spliced and jumped over to the post like that.

that changes everything....Please give me a call. PM sent.

http://farm5.static.flickr.com/4013/...ee2781ef_b.jpg

Well, that was it. Special thanks to Mike (lucky131969) for letting me call him and getting this straightened out. I fixed one problem for sure with my ground strap repair, but caused the other one when I thought I would return the wiring to stock. Seemed like a good idea, but I should have realized it was like that for a reason. I did not get under the car to check out the starter connection for the smaller red (grey at the starter) wire. I would bet the fusible link is blown and who knows where that is inside the wire loom between the starter and alternator. I re-jumped it at the terminal and all is good. 12.6v battery power, alternator charging 14.6v, no codes.

Anyone who powdercoats your alternator. Check for a good ground at many points on the case and the bracket, before you even start it up. If you have no, or bad ground at the rear of the case, you will need a ground strap.

:thumbs:

Do you have any pics of how it is jumpered and what would make the fusible link blow?

Ok so this is a little old but am I correct is reading that there is a fusible link somewhere that causes 1638 and 1637 codes to pop up?

A mechanic just put in a starter for me and I keep getting a charge system fault with these 2 codes.

Tom

No. The fusible link is not the culprit, unless it is somehow blown, which would cause other problems. The OP had a unique circumstance, in which the fusible link was bypassed, by the previous owner. If you just had a starter installed, the first place to look, is the connections at the starter...for security...damage, etc, as shown in the schematic. In reality, you should be taking it right back shop that did the work.

Its still at their shop. They are idiots. Long story, the short version is it was only supposed to be a 1 hr $90 starter install. It has turned into a nightmare.

I was going to take it to the autocrafts center on post here at Redstone AL and do it myself but didnt have to time due to moving.

The "mechanic" crossed the wires when he first hooked up the starter. He thought he blew the alternator so he put a new one in. Its still getting a charging fault with 1638 and 1637 codes. He thinks it has something to do with the terminal L and F now at the PCM.

Ok. Your alternator may not be the problem. Tell him you want the original back.....as putting in the incorrect alternator will cause those codes.

The codes came on with the original alternator in. I went to autozone and got an AC Delco direct GM replacement. Still throwing the same codes.