I have a code 21 that tells me cooling temperture system

Modern reditors are real good till they get dirty. Most all modern engines are made of all kinds of different medals. Because of this their are over 7 different kinds of antifreeze on the market. some engines have EGR valve coolersand they use special antifreeze and these antifreezes don't mix with the other kinds and the mix and turn into a sludge that'll stop everything up and then you have real problems. While doing your coolant sevice be careful not to break anything. I've seen several times where while doing the service on the lower hose they pushed back on an airconditioning line and it rubbed on the fan belt and this contac wore a hole in the hose, failing the airconditioner. the hose in question costs over $400 and the other work to install it and get the sytem working was another $150. Inspect your finished work real well and test it too. Most cars need to warm up all the way before they'll show any cooling system problems So a full warm up including the raditor fans coming on and then going bacl off is required just to see if the work is good. Cooling systems that have waited too long for service need the raditor replaced as the modern raditors don't flush well. After cleaning everything and the new therostate and coolant temperture senser are instaled, it's wise to run over the whole cooling system with an infrared temperture therometer to see if everything is warming up evenly. Part of the raditor can be stopped up even after cleaning and pulling a tralior down the highway way far away from home is not where to find out you did'nt check it good enough. Some raditors won;t clean no matter that you try to do always look at the fact that the raditor protects everything after ther engine oil and the raditor protects the oil too. the temperture being right has become very important as the computer systems tune the engine by what the coolant temperture senser tells it too. so if the senser becomes wrong ( they do often ) or the engine runs too cool,( the therostate open all the time or opens too early) the computer will compensate by turning up the fuel to warm the exhaust and the engine, The rich mixture hits you at the gas pump and also makes the exhaust system parts fail quicker, and in states that check exhaust emissions, might not pass until expensive repairs are done. Follow the manufactures reconmendations for antifreze and don't shop for price or that might be the most expensive savings that you ever got.