Problems for specific GMC Sonoma years:
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Most reported 1999 GMC Sonoma problems
A Loose or worn gas cap may cause Check Engine Light to illuminate.
The heater core under the right side of the dashboard may leak engine coolant which can puddle on the passenger front floor. The loss of coolant may cause an engine overheating condition. Our technicians tell us that removal of the dash board is necessary to replace the heater on these vehicles.
Vehicles equipped whit a 4 speed automatic transmission may develop a harsh 1-2 shift and/or illumination of the Check Engine Light with code P1870 stored. This can be caused by wear of the bore for the TCC isolator and regulator valves in the valve body. This condition does not commonly occur until the transmission reaches normal operating temperature. If the valve body is worn, replacement will be necessary to correct this concern.
The serpentine belt tensioner can fail; it may become noisy and/or the belt may jump off. Replacement of the failed tensioner will be necessary.
A fluid leak may develop from the transmission output shaft seal. This leak may cause the transmission mount to become oil soaked and require replacement of the mount along with the leak repair.
My fuel gauge goes from full to empty then back to full with nothing in between regardless how much fuel is in the tank.
A cover plate on the front of the engine may develop a coolant leak, resulting in an engine overheating condition. This plate covers the location where the water pump was installed on previous versions for this engine. Replacing the gasket for the cover plate and refilling the cooling system is generally all that is required to correct this concern.