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Since this sat for as long as it has, replace the brake fluid. Crack the line at the reservoir and pump it into a container. Don't drain it completely. Only real low so you don't get air into the master cylinder. Then remove the 2 sensors on the brake system. One is on the reservoir and the other is on the line to the rear and left of the reservoir as you are looking at it. Clean them. They may have gum built up from the truck sitting. Those sensors activate the motor for the brakes.
Then reinstall, put clean fluid in, pump more of the bad fluid from the master cylinder, then top the fluid off.
Next is to check the fluid in the power steering. Does it look dark or another color other than clear? If so, replace it. It has water in it to make it look dark from sitting. Then start the truck with the steer tires lifted, then turn far left and far right at least 4 times with the cap removed to remove air that is trapped. Now check to see that you have brake pressure.
Turn the truck off. With the key off, press the brake pedal. You should hear the motor come on and charge the brakes. If not, then one of those 2 sensors is bad and/or the motor is bad on the side of the master cylinder. That is where you are getting the codes and lack of brake pressure from.
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