Two problems related to engine cooling system have been reported for the 1999 GMC Sierra. The most recently reported issues are listed below.
I experienced a sudden onset of a hissing noise coming from under the dashboard. The noise only starts above 1400 rpm and when warm. I have taken it to 2 GMC dealers and 1 independent service shop. All have stated that the noise is water going through the heater core. 1 dealer said that the coolant must have broken down and gelled or scaled into the heater core; therefore, it must be replaced. GMC owners manual states change coolant at 150000 mile or 5 years, if so, why did the coolant break down? this appears to be a major issue and I have read of similar cases. Please help. Dt.
Repeated abs brake failure. This has not been corrected despite numerous attempts to repair problem(s). Heater motor malfunction, repeated wiper arm replacement, tailgate handle malfunction.