Hey guys. I have a 2003 Silverado 5.3 and the service 4wd light came on. I scanned it today and I got 7 codes out of it. They were C0300 C0359 C0374 C0550 B0790 B2725 and U1301. You guys got any ideas what it could be? Thanks.

 

Did you try looking them up online yet? Did you scan your truck or a parts store. If it was a parts store they normally tell you what the codes are.

 

I scanned it myself, but I think it has to be something electrical (like the transmission control module or the 4wd switch) for 7 different codes to appear after it was working fine just the other day. Here are what the codes mean:

C0300 - Rear Speed Sensor Malfunction
C0359 - Four Wheel Drive Low Range (4LO) Discrete Output Circuit
C0374 - General System Malfunction
C0550 - ECU Malfunction - internal write / checksum malfunction
B0790Transfer Case Neutral Indicator Circuit Malfunction
B0790Transfer Case Neutral Indicator Circuit Malfunction
B0790 - Transfer Case Neutral Indicator Circuit Malfunction ATC
B2725 - Active Transfer Case (ATC) Mode Switch Circuit Malfunction ATC
U1301 - Class 2 short to battery

 

You have to be careful....codes are cascading....meaning one code will set others because sensors are dependant on each other....fix the first code first reset and rescan. Also check all your fuses and relays.

Replace the rear speed sensor!

 

Thanks for the tip, but I think I might try replacing the transmission control module first because my friend at the junk yard said he will give it to me for free.

 

I think you have to get the module out of a same build truck. New ones need to be programmed. (dealer)

 

A bad 4WD switch (on the dash) will throw a bunch of codes like that. I have found that it is that switch 90% of the time. If your good with a soldering gun you can open them up and resolder the contacts. Good luck!

 

The ignition switches on these trucks commonly fail after time and cause the tranny's to throw several codes and it will eventually go into limp mode. The switch powers the tranny's electrical's. So you might start running some tests before randomly throwing parts at it to save time, money, and frustration. Believe me I been there. But let us know what you find out so we can help you out bud.