Code o300 checked about everything you can possiblly do and lite still comes on, any idea's 1999 chevy silverado four wheel drive, 5.3 motor auto trans.

I have found out that usually the two ground wires that are attached
to the frame right under the front of the driver's door is the culprit that
causes the 4wd selector switch in the dash to go bad. Chevy had the bright idea
of applying the undercoating and/or not cleaning the point of contact of the
ground wires before they bolted them to the frame therefore overtime moisture,
dirt and corrosion affects the contacts of the threads of the bolts which are
the only source of ground the two sets of wires have. There are 2 things you
will need to do. First you will need to take the bolts out and use a wire brush
to clean down to the metal of the frame as well as the bold threads and ends of
the wire attachments and then reattach the ground wires to the frame (time to
complete - less than 5 minutes). Second you will need to replace the 4wd selector
switch in the dash. You can purchase this online from Amazon (Dorman 901-062
4-wheel drive switch for $31.15 - no tax or shipping and handling). To replace,
gently pull the outer trim of the dash out by using just your fingers. You do
not need to completely remove it, just pull it out far enough so that you can
pull the old switch out of it slot. Then unplug the two plugins located in the
back of the switch. Plug them into the new switch and push the switch back into
the slot and then push the trim back into place (time to complete - less than 5
minutes). This should take care of your problem. Most often, people make the
mistake of just switching out the dash switch and when that does not correct
the problem they then replace the more expensive and time consuming actuator
motor and location indicator on the transfer case that does not need to be
replaced. I should point out that when the Service 4WD light comes on, there
are no codes that show up on the code readers which is awful strange in its
self. I hope this helps everyone with
this problem because I sure wish I knew this before my many costly and time
consuming trips to multiple repair shops including the dealer and none of them
were able to successfully repair the problem. It sure seems like Chevy could
release a repair bulletin so that everyone could fix Chevy's blunder. I bought
my 2005 Silverado new in September of 2005 and this has been the only major
problem I have every had with this truck with the exception of the check engine
light that came on this past spring and the error code was P0446, which was the
Vapor Canister Purge Valve. They have since come out with a new conversion kit
that cost close to $100.00 and is very time consuming to replace. I highly recommend
that you can purchase the original equipment part from Amazon - ACDelco 214-2147
OE Service Vapor Canister Purge Valve for $16.36. You will have to cut the vent
tubing right at the old canister and use a 2 inch long piece of vacuum tubing the
next size up to attach the new canister because the original tubing is hard and
cannot be stretched to remove on to reinstall the new part. The canister is located at the back of the gas tank and can
be accessed without having to even jack up the truck. It clips right onto the
back of the gas tank and has one plug in going into it (time to complete - less
than 5 minutes). Best wishes, Mike Gilbert, St. Joseph, MO

it might have caused someother problem even though u caught the bad bearings

check the four wheel drive fuse.if fuse is good it is probably the tccm.

can not get the lights to come on or go into four wheel drive bought new four wheel drive switch for dash but didnt help

sound like the electronic actuators are not working properly,get your test light out

try selecting from nutreul or less then 3km

You probably have a bad encoder motor.It is located on the side of the transfer case on the drivers side.It is black.The other problem they had with these was the switch but you have already replaced this so your next thing is the encoder motor.Hope this helps.Good luck.

The four wheel drive stepper motor is likely the culprit,they are known to go without notice,they are not cheep so make sure you have power and ground to it,check the plug with a multimeter.

Find out why the engine light is coming on, it is the info u probably need to fix the running rough problem. Most auto parts stores will read the codes stored in your trucks computer for free, write them down, and ask what they mean and how to correct the problem. If u need more info, return to this site w/ codes for further help.

The electric shift solennoid on the transfer case is probably bad,common problem with these.