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2008 Impala LS 3.5L

C0900 means the EBCM is detecting a higher than normal voltage.

I've searched the internet to solve this issue, C0900 code was the only code the car had. The check engine light was not on, the Service Traction Control System would display very intermittently and only for a brief second.

I couldn't find info on any of this and replaced both front ABS vehicle side wiring harnesses. Did not fix the issue.

Long story short, I checked ALOT of things and what I finally did was the following:
Hooked a multi meter to the battery and monitored voltage as I tried to get the car to flash the traction message. When it did flash the message (and make an annoying chime), the voltage spiked into 16v for a split second.

Keeping in mind I did not have any other errors, DTCs or messages regarding battery charge. I cleaned all of the grounds and battery cables prior to this.


At this point I replaced the alternator. And boom... no more issues. I double checked my battery voltage, tried to get it to "over charge" briefly turning on the headlights and rear defrost at the same time. And everything cleared up. So it seems the voltage regulator built into the alternator was having issues.

I hope this helps someone out there someday!
-I apologize for lack of pictures.
 
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