Need electrical help! Code P1637
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
If the PCM determines and commands the DUTY CYCLE,,,, what if the PCM is not getting the correct voltage. The PCM has several 12 VDC power supplies. One is supplied by a wire that is HOT AT ALL TIMES.
The other is powered when you turn the ignition ON. That supply is HOT in ON and Start. Monitor the HOT in On and Start power to the PCM and see if the erroe coinsides woth the DTC.
The HOT in On and Start power voltage should be the same or very close to BATTERY VOLTAGE. Any difference would be caused by dirty defective ignition switch contacts for that output.
Im digging deep here!
The other is powered when you turn the ignition ON. That supply is HOT in ON and Start. Monitor the HOT in On and Start power to the PCM and see if the erroe coinsides woth the DTC.
The HOT in On and Start power voltage should be the same or very close to BATTERY VOLTAGE. Any difference would be caused by dirty defective ignition switch contacts for that output.Im digging deep here!
Thread Starter
Instructor
Joined: Mar 2010
Posts: 130
Likes: 2
From: Saint Louis MO
Ok, I sent the PM to Evil Twin to try to get his opinion. To the best of my knowledge, the unit is Valeo. When I purchased it, all of the data for the item said "Valeo 110 amp" etc. When I replaced it, I recall the two units looking identical, but I don't know how to prove that the new one is a Valeo unit, as I do not recall any manufacturer lables on the unit itself.
Thread Starter
Instructor
Joined: Mar 2010
Posts: 130
Likes: 2
From: Saint Louis MO
Well, it appears I have solved the problem! The issue was in fact the alternator.
I received a new unit from a forum sponsor (a genuine GM alternator) and the problem has been fixed.
Fortunately, the night manager kid at the advance auto parts where I bought the reman alternator has said he will take that unit back, so that will help recover some of the cost.
Only bad part? The new alternator was packed very, very poorly. I am going to call about it in the morning, but basically the 4-way electrical connector on the alternator was damaged in transit to me. The alternator was very poorly packed - basically just put in a box loose and shipped - the banging around broke part of the electrical connector off.
As a result, the plug doesn't fit quite right - it the plug isn't inserted just right, you will get codes as the unit loses communication. If I plug it in a certain way, I'm all good.
Hopefully the seller will allow me to swap the unit for one without damage, and will carefully ship the replacement unit. However, regardless of that outcome, the problem was the alternator, and the reman unit was somehow lacking in the communication circuit area, and though it was outputting current correctly, it was not sending the right messages to the PCM, and therefore threw codes.
-David
I received a new unit from a forum sponsor (a genuine GM alternator) and the problem has been fixed.
Fortunately, the night manager kid at the advance auto parts where I bought the reman alternator has said he will take that unit back, so that will help recover some of the cost.
Only bad part? The new alternator was packed very, very poorly. I am going to call about it in the morning, but basically the 4-way electrical connector on the alternator was damaged in transit to me. The alternator was very poorly packed - basically just put in a box loose and shipped - the banging around broke part of the electrical connector off.
As a result, the plug doesn't fit quite right - it the plug isn't inserted just right, you will get codes as the unit loses communication. If I plug it in a certain way, I'm all good.
Hopefully the seller will allow me to swap the unit for one without damage, and will carefully ship the replacement unit. However, regardless of that outcome, the problem was the alternator, and the reman unit was somehow lacking in the communication circuit area, and though it was outputting current correctly, it was not sending the right messages to the PCM, and therefore threw codes.
-David
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
Thats EASY! You either have a compromised connection at the starter solenoid OR you have a bad /blown fuseable link. Check the wire continuity between the solenoid and alternator pin D. If the fuse link is bad,,,, replace it..
BC
BC
BC
BC
Drifting
Joined: May 2008
Posts: 1,517
Likes: 319
From: Hewitt TX
Where is this fuseable link located if I need to replace it?
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Intermediate
Joined: Mar 2011
Posts: 27
Likes: 0
From: Merritt Isl. Florida
Another one bites the P1637 dust!
I'm a new member to the Forum as of today.
I'm not sure who this is going to, I'm simply piggybacking on the topic that matches my problem the closest.
I own a 2002 automatic. Everything is stock except a new battery a few months ago.
Yesterday, on my way home from work, I got "Charging system fault" followed by "Service vehicle soon" on my display. I made one stop on the way, and she almost didn't re-start due to low battery charge. Once home, I ran the codes twice. First time displayed many codes which made historical sense (recorded all) except for P1637. I then deleted all codes and ran them again. Two codes remained, P1637 and C1214. I'm mainly concerned with 1637 right now, but if you see a correlation with Traction Control Sys (TCS) 1214, please advise.
I've done an extensive amount of reading and am trying to rule out everything prior to replacing the PCM. I've performed several tests to first rule out the generator but could use some advise on testing the L & F terminals.
I will review with whomever replies the tests I've performed thus far.
Thanks in advance, Home Grown
I'm not sure who this is going to, I'm simply piggybacking on the topic that matches my problem the closest.
I own a 2002 automatic. Everything is stock except a new battery a few months ago.
Yesterday, on my way home from work, I got "Charging system fault" followed by "Service vehicle soon" on my display. I made one stop on the way, and she almost didn't re-start due to low battery charge. Once home, I ran the codes twice. First time displayed many codes which made historical sense (recorded all) except for P1637. I then deleted all codes and ran them again. Two codes remained, P1637 and C1214. I'm mainly concerned with 1637 right now, but if you see a correlation with Traction Control Sys (TCS) 1214, please advise.
I've done an extensive amount of reading and am trying to rule out everything prior to replacing the PCM. I've performed several tests to first rule out the generator but could use some advise on testing the L & F terminals.
I will review with whomever replies the tests I've performed thus far.
Thanks in advance, Home Grown
Last edited by Home Grown; Mar 26, 2011 at 11:03 PM.
Tech Contributor
Joined: Jan 2007
Posts: 19,341
Likes: 1,122
From: Dyer, IN
I'm a new member to the Forum as of today.
I'm not sure who this is going to, I'm simply piggybacking on the topic that matches my problem the closest.
I own a 2002 automatic. Everything is stock except a new battery a few months ago.
Yesterday, on my way home from work, I got "Charging system fault" followed by "Service vehicle soon" on my display. I made one stop on the way, and she almost didn't re-start due to low battery charge. Once home, I ran the codes twice. First time displayed many codes which made historical sense (recorded all) except for P1637. I then deleted all codes and ran them again. Two codes remained, P1637 and C1214. I'm mainly concerned with 1637 right now, but if you see a correlation with Traction Control Sys (TCS) 1214, please advise.
I've done an extensive amount of reading and am trying to rule out everything prior to replacing the PCM. I've performed several tests to first rule out the generator but could use some advise on testing the L & F terminals.
I will review with whomever replies the tests I've performed thus far.
Thanks in advance, Home Grown
I'm not sure who this is going to, I'm simply piggybacking on the topic that matches my problem the closest.
I own a 2002 automatic. Everything is stock except a new battery a few months ago.
Yesterday, on my way home from work, I got "Charging system fault" followed by "Service vehicle soon" on my display. I made one stop on the way, and she almost didn't re-start due to low battery charge. Once home, I ran the codes twice. First time displayed many codes which made historical sense (recorded all) except for P1637. I then deleted all codes and ran them again. Two codes remained, P1637 and C1214. I'm mainly concerned with 1637 right now, but if you see a correlation with Traction Control Sys (TCS) 1214, please advise.
I've done an extensive amount of reading and am trying to rule out everything prior to replacing the PCM. I've performed several tests to first rule out the generator but could use some advise on testing the L & F terminals.
I will review with whomever replies the tests I've performed thus far.
Thanks in advance, Home Grown
Did you perform the tests from the service manual?
Intermediate
Joined: Mar 2011
Posts: 27
Likes: 0
From: Merritt Isl. Florida
Thanks Lucky,
The service manual tests you sent me is something I found early in my Forum search. It is one of two test breakdowns I've saved in a file among other helpful tips.
1) I dint own a manual so thanks for sending it to me.
2) I dint own a test tool so I have to test with multimeter and/or test light.
3) Many of the listed tests refer to a link to an electrical diagram for assistance. None of the links open to include yours. this is the level of detail I need at this time.
The service manual tests you sent me is something I found early in my Forum search. It is one of two test breakdowns I've saved in a file among other helpful tips.
1) I dint own a manual so thanks for sending it to me.
2) I dint own a test tool so I have to test with multimeter and/or test light.
3) Many of the listed tests refer to a link to an electrical diagram for assistance. None of the links open to include yours. this is the level of detail I need at this time.
Intermediate
Joined: Mar 2011
Posts: 27
Likes: 0
From: Merritt Isl. Florida
BTW
Its an honor to have this dialog with such a popular, well established, Senior Member like yourself. Nice engine pic too!
In the short time I've been surfing the Forum, I've run across your name/assistance several times.
Thanks, Home Grown
Its an honor to have this dialog with such a popular, well established, Senior Member like yourself. Nice engine pic too!
In the short time I've been surfing the Forum, I've run across your name/assistance several times.
Thanks, Home Grown
Drifting
Joined: Jan 2010
Posts: 1,447
Likes: 1
From: Katy TX
I just go through dealing with the same issue tonight. On the way home from work I get the "charge system fault" message out of the blue and battery is displaying 11.6 volts on the dic. By the time I got home the dic was showing low voltage and I had no radio, no speedo or tach readout, pass window would not raise up, tcs 1214 service traction control message, etc was showing up. I take batt to autozone to get recharged and I let the engine cool off and visually checked the connections on the starter and everything looked fine. I took a wrench and slipped my hand through the header and tightned the bolt where the batt, alt and fuseable link come together...picked up batt from autozone and then went to restart the car and I get the code 1637 again and batt is not charging. I disconnect the batt and undo the bolt a bit on the starter again where the 3 wires reside. I then spray some wd40 on the bolt and post and 3 tabs of alt, batt and link and then retightened the bolt.... I start the car and let it idle for 10 minutes while I adjust the settings on the nav and batt is now charging and all code have went away. How does that bolt come loose in the first place?
Last edited by All_Motor_C5LS6; Jun 13, 2011 at 11:34 PM.
Drifting
Joined: Sep 2007
Posts: 1,649
Likes: 50
From: Goldsboro NC
To the OP, awesome job on the troubleshooting! Good luck to the rest of you guys. I know Lucky and Bill has to think sometimes they sound like broken records. Rinse and repeat year after year. Even though I don't have this problem (knocks on wood) thank both of you guys for the help you do provide on issues, as I have searched multiple threads for various issues that have come to light over the years.
Melting Slicks
Joined: May 2000
Posts: 2,305
Likes: 5
From: Orlando,Fl,USA
I am really hoping someone can help with this - its getting very frustrating.
Car is a 2000 convertible.
At startup, car sets code P1637 - generator L-terminal fault. Originally, it was fairly intermittent, and would sometimes be accompanied by "service vehicle soon" message on DIC - back in like May.
Now, I get the code and message at almost every ignition. After a few minutes of running, the code usually clears itself and shows only as a history code, not current, and the "service vehicle soon" message stops.
1: Alternator has been tested good by Advance Auto Parts on a bench test
2: Went ahead and replaced alternator anyway thinking maybe it was bad - it tests good as well.
3: Continuity has been checked on L-terminal circuit from the connector on top of alternator back to red PCM harness.
4: When operating, car shows good voltage of 13V - 14.5V on voltmeter in instrument cluster.
Unfortunately, I took the car to the stealership, and they said they ran the flow chart from the service manual (same one I read) and got the result that the alternator is bad - it isn't. They didn't even test the alternator, just said that was the flow chart result. Basically, they were making excuses in my opinion, and wanted to sell me an alternator.
The flow chart in the service manual basically appears to give three possible outcomes - bad alternator, bad wiring on the circuit, or bad PCM.
Alternator tests good, circuit continuity tests good - I can't believe the PCM would be bad since the car otherwise runs absolutely fine.
Any ideas? Does this make any sense? Please, those with electrical experience, please help!
-David
Car is a 2000 convertible.
At startup, car sets code P1637 - generator L-terminal fault. Originally, it was fairly intermittent, and would sometimes be accompanied by "service vehicle soon" message on DIC - back in like May.
Now, I get the code and message at almost every ignition. After a few minutes of running, the code usually clears itself and shows only as a history code, not current, and the "service vehicle soon" message stops.
1: Alternator has been tested good by Advance Auto Parts on a bench test
2: Went ahead and replaced alternator anyway thinking maybe it was bad - it tests good as well.
3: Continuity has been checked on L-terminal circuit from the connector on top of alternator back to red PCM harness.
4: When operating, car shows good voltage of 13V - 14.5V on voltmeter in instrument cluster.
Unfortunately, I took the car to the stealership, and they said they ran the flow chart from the service manual (same one I read) and got the result that the alternator is bad - it isn't. They didn't even test the alternator, just said that was the flow chart result. Basically, they were making excuses in my opinion, and wanted to sell me an alternator.
The flow chart in the service manual basically appears to give three possible outcomes - bad alternator, bad wiring on the circuit, or bad PCM.
Alternator tests good, circuit continuity tests good - I can't believe the PCM would be bad since the car otherwise runs absolutely fine.
Any ideas? Does this make any sense? Please, those with electrical experience, please help!
-David