You must have a 1500. That's the only one I can find that came with a 4.3L. There are two power brake versions available. One has the common and reliable vacuum booster. There is no way to monitor its performance with a warning light. The other system is called "hydro-boost" and runs off pressurized power steering fluid. That system was developed for use with diesel engines because they often don't have enough vacuum to run the regular system. They might have used it on your truck for the same reason.
I don't know how they are monitoring it for proper operation unless it is watching the power steering pressure. Check the power steering fluid to be sure it's full. If it's low, look for signs of leakage. If you notice any braking or steering problems, it's time for an inspection of those systems. If everything seems to be working correctly, I'll put in a call to another expert who may be familiar with what triggers that warning message.
Also check the brake fluid level in the reservoir. If it's just half full, you can try adding a little from a clean, sealed container of new fluid, but don't fill it to the top. There needs to be room in the reservoir to accept the fluid that will return there whenever new front brake pads are installed in the future. If the level is REAL low, suspect a fluid leak. Be absolutely CERTAIN you do not get the slightest hint of power steering fluid, or any other petroleum-based product, like engine oil, mixed in with brake fluid. Don't leave any container of brake fluid uncapped for very long as it will such moisture out of the air.
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Friday, July 15th, 2011 AT 7:18 PM