2005 Grand Am Charging system problem


#1

I replaced the battery and the alternator about 2 weeks ago. The new (rebuilt delco from autozone) lasted about 4 days. They replaced it. It started out at putting out 14.5 volts, and now is down to 13.3. They tested it and said the regulator is bad. I found a parasitic battery drain of about 1.75 amps, that pulses back and forth between .09 ma and 1.75 amps about every 6 or 7 seconds. I have pulled fuses until my fuse puller is worn out… I’m out of ideas.


#2

You never said what the end-symptom is (or are). Presumably, you keep ending up with a dead battery? Or perhaps a battery that seems dead? I’ll further have to resume that you are turning the key and getting symptoms of a bad battery, such as a weak crank or something. In any case, those GM battery cables are known for developing corrosion, including down under the insulation. So have you verified an actual low battery voltage during what - I am presuming - is a no/weak crank episode.

On the parasitic drain, hopefully you are making sure that all of the car’s modules have been given time to go to sleep before doing the parasitic drain check. And hopefully you’re not doing things like opening and closing doors while in the midst of it since that wakes up the BCM at minimum.

Finally, have you made it to the fuses in the underhood box?


#3

The end problem at this point is that I keep ending up with a dead alternator. I have been working on this for a month, so I keep close tabs on the battery voltage, as wall as the alternator output. The car starts great, again, at this point, because I don’t let the battery rung down, there is no draggging of the starter or hard starting, it fires right up. The original problem, was that it was runnning the battrery down over a few days, until it finallly destroyed the battery… New battery, and on second new alternator that is slowly loosing voltage output. And yes, I am making sure not to wake the car up when testing for parasitic drain. If I do, I wait until it begins to drop again. The fusebox under the hood is where I started. I have pulled every fuse and relay there. Originally, when I pulled both fuses to the inside fuseboxes, i lost the excessive amp draw, not one or the other, but both, but that isn’t happening anymore. Thanks. Brad


#4

And also, I cannot seem to find the PCM


#5

Found it!


#6

Here is a link that may help you figure where the trouble is at. Normal current draw should be less than 50 milliamps for most vehicles.

http://www.aa1car.com/library/battery_runs_down.htm


#7

Thanks Cougar


#8

You could use a laser temperature meter to measure the temp of the fuses one by one to spot which circuit is drawing a lot of current. The hottest fuse is the circuit drawing the most current. Or, less high tech, you could use a thermocouple.

When you say the alternator voltage decreases, do you mean when you first start the car it reads 14.5 volts, then over time with the engine running it drops to 13.3 volts? If so, that’s likely normal, as the alternator voltage will drop as the alternator determines the battery is nearing full charge. Monitoring alternator voltage as an alternator diagnostic technique is becoming less effective with new cars as often the ECM gets involved in the charging process these days.


#9

Chances are it was the battery continually running down that has been killing the alternators. Alternators are only designed to run the car’s systems and just do minor topping off charges of the battery. If your battery kept being drawn down and the alternator kept having to recharge, that would explain the recurring alternator issues.

So I would keep chasing the parasitic draw.


#10

I have 4 wires going to my alternator. According to the wiring diagram at Autozone.com, I have a red and a grey one on the plug, going to the pcm, on my car those 2 are red and orange. Then I have a heavy gauge red one going to the solenoid, then a smaller gauge one (Gen Batt) that is orange on the wiring diagram, and red on my car. On the diagram it is not clear where it hooks to, on the alternator, but both of the 2 that aren’t on the plug hook to the big post on top. 2 funny things. I took apart the fusebox under the hood. The (Gen Batt) fuse has an outgoing orange wire, like the schematic says, but its red when it gets to the alternator. If I remove it, the car goes to sleep in less than 30 minutes. If I hook it back up, I get high draw again.


#11

Also, the plug has a place for 4 wires, but only 2 are attached, and there are 4 pins in the female receptacle.


#12

Heres the diagram


#13

I just made a startling discovery. What was taped up to look like 3 wires, is really only 2, and only one of them comes from anywhere:


#14

Well ok. I pulled back the sheathing about a foot, and found the cut red wire. So now I have a red and an orange wire to hook to the PCM (which is probably bad). After digging around, I beleive that I have the LA1 engine (V-6 3.4L), which, according to the diagram above is all that goes into the plug. So I am assuming that this was some kind of PCM bypass attempt that left the alternator going full blast all the time. Funny that I drove it for 2 years like that on the first one. I guess the Duralast remans just couldn’t take the stress.


#15

From the diagram it appears the 0.35 Red wire is used by the PCM to enable the alternator. The PCM might want to disable the alternator at certain times to reduce engine mechanical load, like during cranking, or if the AC compressor is briefly taking a lot of engine power, or at idle with the auto transmission in gear, etc. It’s probably used by the PCM to prevent stalling/drivability situations.

The 0.35 gray wire is probably used by the ECM to power the internal magnetic field in which the alternator’s rotor spins. As the rotor – which is just a coil of wires — spins inside the magnetic field, the rotor’s wires produce voltage and current. The higher the field strength, the higher the voltage the alternator produces. As the rpms increase, the field strength must decrease to keep the same output voltage. Otherwise the battery would overcharge. That’s why the PCM is involved with calculating the correct field coil current.

The 0.35 orange wire appears to just be the battery voltage input to the regulator. It uses that to decide how much the alternator’s output voltage should be.

The 8 red wire is the main voltage/current output from the alternator used to charge the battery. It appears to connect to the battery via a starter solenoid terminal. Note that there’s a fusible link in that part of the circuit too, which would cause the alternator to fail to charge the battery if it blew. (The dotted line ---- thing in the upper left hand corner is a little unclear what that means, but I think it just means those points are connected.)

fyi, when a wire is denoted “8 red” I think that means the copper conductor inside has a cross sectional area of 8 mm^2; i.e. an 8 red is a much thicker wire than a 0.35 red.


#16

Thanks for the replies. By the time I got it taken apart and put back together, I pretty much figured out what everything was doing.Using the red wire to bypass the PCM was rather ingenious, unfortunately it cause the key off parasitic drain problem I was having; (by backfeeding through the alternator) After I put it back the way It should be, it started and ran great. The second time I started it, the dash lights, gauges, radio and A/C were not working. The only thing I can find that these things have in common is a ground splice pack, Maybe its a coincidence, and I put to much pressure on it (where ever it is) when I was taking the dash apart. Hopefully that is it.