1999 GMC Sonoma Repair and Maintenance

A guide to problems, costs, maintenance and repair for your 1999 GMC Sonoma

1999 GMC Sonoma Problems

Heater Core Under Right Side of Dashboard May Leak Engine Coolant

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.

Check Engine Light With Code P1870

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.

Flush cooling system every 60,000 miles

GM recommends replacing the engine coolant at 100,000 miles; however, our technicians tell us that the coolant may become contaminated and require a complete cooling system flush every 60,000 to 70,000 miles.

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