I have an '08 Cobalt LT and the past 3 weeks my Service Engine Soon light comes on for a split second while drive at random. Two of the three times, the HU reboots also. Stereo was on all 3 times, and the 2nd time the bass was pounding hard. Not so much at all the other 2 times though. Heat was on low all 3 times.

I took it to the shop and the scantool found no codes stored. They mentioned getting the alt rewound to a higher amperage as the amp was demanding too much (that was the extent of their diagnostic - a verbal response and the scantool). That and addition to using the heater put it over its limit.

My system was fine all summer with the A/C on at times, so why it is acting up now in relation to the stereo system (amp being the big culprit apparently) seems odd. Unless the toll is just being noticed NOW on the battery and/or alt?

I have no idea what the stock amperage is on my alt.

 

Stock output should be 110amp

Is it a denso style?

Is it a 5 or 6 rib pully?

You might be able to mount a stock alternator from a 1995 cadillac deville 4900 and switch out the pulley if needed. This alternator puts our 140- amp stock. It is a CS-144 style.

This is a fairly common swap for a lot of GM guys.

 

I suspect the 2.2 cobalt comes with a 90 amp alt. The car can draw a LOT of power if you have all the options on at once.
rear defrost can pull 20 amps, heated seats, head lights, running lights, heated mirrors, but thats probably only the SS version. heater fan only draws a couple amps.
Anyway, that amp can only pull 25 amps, so its not the problem.
What kind of interface did you use when you replaced the head unit?

 

I suspect there are several factors conspiring all at once here. The cold affects the battery and as stated above the defroster etc. will consume much of the alternators output. Due to the increased demand your battery may be aging prematurely, just a guess there. Combine these with a relatively weak factory alternator and I expect you would see this happen after listening to it loud for a while. A higher output alternator should solve this.

 

Where is the best place to buy an HO alt in Canada?
140Amp range give or take a few.

 

Not sure what kind of style the alt is or pullies.

As for the interface... I have no idea. I had it done at East Hamilton Radio. I am sure it is on the receipts, can't recall off hand though. I know it has the PAC SWI though for the steering wheel. Axxess? That rings a bell.

For now, I just drive around at really low volume. However... there is the alt whining noise. Up and down with the gas she goes. Very annoying.

I want to get a new battery as well to replace the fact. one once I figure out the best way to correct the alternator issue. I don't really want to run one beside the primary, and don't really want another AC Delco. Interstate? Optima Yellow Top?

25 amps?? This amp draws ~ 100 amps at least according to the stereo shop (prob meaning when I had it cranked and the SES light came on?). It is one bad *** amp. http://www.audison.eu/index_main.php?Section=LRX51k

Thx.