2001 Suburban.. Code Reader Won't Read

Reader works fine on another 01 3/4 ton GMC,and my other car.

Grounds at Pins 4,5 on the DLC are good. Power to 16

CEL is not on..has not come on.

Message centre flashes: Lo fuel, then Batt.,then security,then service 4wd.

Fuel and temperature gauge pulse on and off.(With the key on and engine off)
Oil Pressure and voltmeter work fine.
Gear Selector illuminator not working.

Cig. ligher works fine.

Bat. voltage is fine,drops under load(engine off) and comes back up when starts.

ABS light on dash..starts dim,then gets bright,then goes out,repeats.
Air Bag light is on.

Truck runs fine. Everything else seems ok.

This started about a month ago. The lo fuel light came on. I put some GM stuff in it to fix it
and it appeared to work.

3 days ago..it started,quit,started,quit,started,quit..then the security light came on and stayed on. No other problems.2 days ago all the above started.

ANY help as to where to start looking is greatly appreciated. THANK YOU!

Reader works fine on another 01 3/4 ton GMC,and my other car.

Grounds at Pins 4,5 on the DLC are good. Power to 16

CEL is not on..has not come on.

Message centre flashes: Lo fuel, then Batt.,then security,then service 4wd.

Fuel and temperature gauge pulse on and off.(With the key on and engine off)
Oil Pressure and voltmeter work fine.
Gear Selector illuminator not working.

Cig. ligher works fine.

Bat. voltage is fine,drops under load(engine off) and comes back up when starts.

ABS light on dash..starts dim,then gets bright,then goes out,repeats.
Air Bag light is on.

Truck runs fine. Everything else seems ok.

This started about a month ago. The lo fuel light came on. I put some GM stuff in it to fix it
and it appeared to work.

3 days ago..it started,quit,started,quit,started,quit..then the security light came on and stayed on. No other problems.2 days ago all the above started.

ANY help as to where to start looking is greatly appreciated. THANK YOU!
Sometimes a boy can not do a mans job.
A code reader will not do that job.
You will need a high end scanner to get ABS,Sir and body and trans and havc codes.