Help: Electrical Problem on ABS, Heater and A/C

[lobocharlie]

Guys I need some help for the last week when I start my truck the ABS light, Brake light, the darn chime goes off continuously and the service brake system flashes on the dash board. When they are on the Anti brakes don’t work. If I continue to drive about 5 miles they will go away. Then the Anti lock seems to work.
[FONT=&quot]1. [/FONT]Truck is completely stock 2003 Duramax

[FONT=&quot]2. [/FONT]I cleaned the ground under the driver door
[FONT=&quot]3. [/FONT]I cleaned the ground under the driver battery tray
[FONT=&quot]4. [/FONT]I checked the ground wire at the ABS module looks good
[FONT=&quot]5. [/FONT]I have ground at the Speed sensor
[FONT=&quot]6. [/FONT]I check the speed sensors 900 ohms
[FONT=&quot]7. [/FONT]The code that I get is C0200 when I check the ABS system with a Snap on MT 2500

The other big thing is when I turn the heater switch on nothing works( fuses are fine) and it triggers the same dash board indicators that I mentioned above immediately. Why would the function on the heater or air conditioner affect the ABS stuff?
[FONT=&quot]1. [/FONT]There is a U code in the history loss communications to the heating and AC module. I don’t remember the number off hand.


[FONT=&quot]Please Help[/FONT]

 

[03_dirty_max]

I know this is a old post but i'm having the exact same issue. Does anyone have an answer to what might be causing this?

 

[lobocharlie]

I should of posted my fix. Mine was the ignition switch. It was only sending 4 volts through the fuse box. I replaced it and bam 12 volts and everything cleared up