Low Coolant Level with No Sign of External Leaks. The Low Coolant Warning light is on and there are no signs of a visual leak. Pressure testing the cooling system may or may not show an internal leak (loss of pressure). There may also be a complaint of transmission fluid leaking from the vent on top of the transmission; poor shift quality; or a shuddering from the transmission. There is an internal failure of the automatic transmission oil cooler, allowing coolant to mix with transmission fluid. Possible faulty coolers were built between 6/6/2013 and 8/4/2013.