Voltage problem
01-13-2012, 04:16 PM
#1
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Voltage problem On monday on my way to work my check gauges light came on. My volts were reading around 12 volts. That night on my way home headlights started dimming and lost all power. So I figured altinator. I got a new altinator, and put it on lastnight. Took it on test drive and same thing happened. So I figured battery. Put a new red top in today, and volts are 14.3 until I hit breaks. The check gauges light comes on and volts drop to around 11. Same thing happens when I turn heat, headlights, or stereo on. Im stumped any help would be greatly appreciated. This is on a 98 Trans Am. Thanks in advance.
01-13-2012, 10:02 PM
#3
do you have a multimeter? use that to measure your numbers at the battery. does the car crank slow or does it crank like you would expect a new battery to be able to? sight unseen, i'm guessing you got a bad alternator or you have a cable/cable connection issue.
01-13-2012, 10:54 PM
#4
its the connection in the exitor plug, the wire comes loose from the pin over time. i spent a weekend fixing it. you need to yank the wire out from the plug. if the plug is ok, splice some wire onto it to add some length to it and put the wire back into the pin in the connector. Or the quicker but more expensive way is to buy a new plug with a wire off ebay or from kragen.
01-13-2012, 11:12 PM
#5
its the connection in the exitor plug, the wire comes loose from the pin over time. i spent a weekend fixing it. you need to yank the wire out from the plug. if the plug is ok, splice some wire onto it to add some length to it and put the wire back into the pin in the connector. Or the quicker but more expensive way is to buy a new plug with a wire off ebay or from kragen.
01-14-2012, 08:12 AM
#7
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I would tend to agree with slowpoke96z28's diagnosis, as long as your not getting a good output from the alternator. I know this was something I heard about when my motor was out and I double checked it.
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01-15-2012, 01:38 PM
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I checked with my multimeter, at the batery onley, then at the cables, and on the drivers side at the fuse box. All read the same 12.3ish, car was not running. I had Advance check it today, and they said the alt. Was not charging at low rpms. So Im exchanging it today and will see what happens. I will also check my plug and wire too while Im doing it. Thanks
01-16-2012, 02:06 PM
#10
If you run into that issue. Look up my thread "the fix for my endless alternator failures"
https://ls1tech.com/forums/generatio...-failures.html
hope you don't have that problem. Replace the connector to the alternator regardless, they go bad over time and will cause you further headache.
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69AARVIPER (09-02-2023)
01-17-2012, 11:35 PM
#12
fwiw the alternators at least in my 2002 and I suspect going back to 1998 technically don't have an "exciter wire" connection in the traditional sense. The voltage regulator in the alternator is not simple like they used to be, they are now a microprocessor. And from reading my 2002 service manual, the LS1 has a 4 wire plug in to the alternator.
According to DTC P0620 description, the PCM tells the voltage regulator to turn on or off with a 5 volt signal, and once the alternator is turned on or there is 5 volts applied on the L terminal of the voltage regulator, then the regulator controls the alternator's output. Now this is described for 2002 LS1. I don't know if other years are different- that a different voltage regulator is used in the alternator, this can be very important. A good read at the link below describes this, look for "Section 4: 10. The CS terminals are designated as follows."
That being said, it would not surprise me that you are getting reman'd alternators from the parts stores with the wrong voltage regulators in them, rather than them being cheaply mass produced. And i am somewhat curious how they know at the parts store how to properly check alternators and what their machine is actually doing.
But regarding the voltage problems,
a low or no voltage can be caused by a few things. One is bad brushes in the alternator, which generally don't happen unless the alternator is old, has many hours on it, or sat for a long time in a wet or inhospitable environment. Another is a bad or burnt out internal regulator (microprocessor) in which case you need a new one or a whole new alternator. The other and more common is a bad wire connection of the 4-pin plug to the alternator. Either the 5-volt turn on signal known as the "exciter wire connection" is bad somewhere between the regulator and pcm. And also check for a DTC the PCM might not be turning the alternator on for some other reason. So this would cause a no output condition. Another cause is a bad sense wire connection usually marked S on the regulator, this connection goes to battery + or very close to the battery positive terminal, the purpose is to sense correct battery voltage. If this connection is bad and has higher than normal resistance, then this will cause HIGHER output voltage and is typically the only cause of an alternator outputting 15 volts or more- the other cause of high voltage for the same reason is bad electrical system ground connections either at the battery post or the alternator regulator to ground.
so that's 2 terminals of 4 described. The other two, the P terminal and F/I terminal are well described in the link. If either of these two connections to the PCM are bad, it can likely cause poor output or no output from the alternator. And most times the bad connection is the 4 pin plug that plugs into the alternator.
http://oljeep.com/gw/alt/edge_Altern...html#Section_4
According to DTC P0620 description, the PCM tells the voltage regulator to turn on or off with a 5 volt signal, and once the alternator is turned on or there is 5 volts applied on the L terminal of the voltage regulator, then the regulator controls the alternator's output. Now this is described for 2002 LS1. I don't know if other years are different- that a different voltage regulator is used in the alternator, this can be very important. A good read at the link below describes this, look for "Section 4: 10. The CS terminals are designated as follows."
That being said, it would not surprise me that you are getting reman'd alternators from the parts stores with the wrong voltage regulators in them, rather than them being cheaply mass produced. And i am somewhat curious how they know at the parts store how to properly check alternators and what their machine is actually doing.
But regarding the voltage problems,
a low or no voltage can be caused by a few things. One is bad brushes in the alternator, which generally don't happen unless the alternator is old, has many hours on it, or sat for a long time in a wet or inhospitable environment. Another is a bad or burnt out internal regulator (microprocessor) in which case you need a new one or a whole new alternator. The other and more common is a bad wire connection of the 4-pin plug to the alternator. Either the 5-volt turn on signal known as the "exciter wire connection" is bad somewhere between the regulator and pcm. And also check for a DTC the PCM might not be turning the alternator on for some other reason. So this would cause a no output condition. Another cause is a bad sense wire connection usually marked S on the regulator, this connection goes to battery + or very close to the battery positive terminal, the purpose is to sense correct battery voltage. If this connection is bad and has higher than normal resistance, then this will cause HIGHER output voltage and is typically the only cause of an alternator outputting 15 volts or more- the other cause of high voltage for the same reason is bad electrical system ground connections either at the battery post or the alternator regulator to ground.
so that's 2 terminals of 4 described. The other two, the P terminal and F/I terminal are well described in the link. If either of these two connections to the PCM are bad, it can likely cause poor output or no output from the alternator. And most times the bad connection is the 4 pin plug that plugs into the alternator.
http://oljeep.com/gw/alt/edge_Altern...html#Section_4
01-17-2012, 11:46 PM
#13
http://grannys.tripod.com/2ndgenLS1instructions8.html
from this if it's partially correct, the 1998 PCM sent a 12v signal to the L terminal. so 1998 models have an alternator with a different voltage regulator than in 1999+ models.
But it is incorrect when it states '99 had voltage control incorporated into the PCM, it does not and according to my GM 2002 service manual that function is controlled by the alternator's internal voltage regulator.
LS1/Delco Alternator Wiring...The LS1 alternator output is triggered by a low voltage signal from the LS1 PCM's C-2 "red" connector, pin 15. This wire is contained within the stock LS1's engine harness. The '99-newer LS1 had proper control of the voltage regulator incorporated into the PCM. The '98 LS1 PCM did not, and the circuit needs modification to prevent alternator damage. For proper operation, alternator terminal "L" (red wire) needs to be connected to PCM red C-2 connector's pin 15 thru a 470 ohm resistor. Simply snip the red wire at a conveinant location, and solder the resistor in series with the wire.
But it is incorrect when it states '99 had voltage control incorporated into the PCM, it does not and according to my GM 2002 service manual that function is controlled by the alternator's internal voltage regulator.
