2005 Chevy Impala. Question: The Temperature Gage goes pass the 220 mark and kicks down, but when turning the heater on, does not give out heat. It has to jump up several times pass the 220 mark before throwing out heat in the car. I had the car tested and it came back with the po122 reading. What do I need to do to correct this problem?
Answer: This sounds like a common problem of air pockets in the cooling system. Air pockets will cause the temperature gauge to swing erratically from normal operating temp or higher, down to a lower or lower than normal reading, and cause no heat from the vents. When the air pockets get into the heater core, the core cannot transfer heat from the core into into the car. The heater core must be full of coolant in order to transfer heat.
A cause for these air pockets is either a low coolant level caused by a leak or a blown headgasket. Leaks can be from a leaking water pump or "Crossover Manifold". A pressure test of the system would be needed to find a leak. If no external leaks are found, then I would suspect a blown head gasket. When this happens, antifreeze is burned in the engine and a leak may not be evident, except on the very back of the rear cylinder head, as seen from under the car on the passenger side. The rear seems to be most common. Removing the spark plugs and inspecting for evidence of burning coolant will confirm this. Scan code P0122 is throttle position sensor voltage low and would have nothing to do with the heat problem you are having.
Radiator Fans Will Not Come On
The fans in my car will not come on unless I unplug the temp sensor at the block (which has been replaced and functions properly). Because of this I had an overheating problem, now I just keep it unplugged, but I'm afraid that the fans being on constantly, I am killing my alternator. Someone told me it may be the cars computer. Any suggestions?
Answer: It could be the vehicle's computer, but there are a few things you should check first. You need to be absolutely positive that the temperature sensor is functional. When you unplug it, you are opening that circuit, so there could be a short elsewhere in the circuit or inside the computer. Normally, the fans should not run with that sensor unplugged. Check the fan relay by switching it with another one to see if the problem is fixed. Try and scan the vehicle to see if there are any trouble codes that lead to the problem. A computer is an expensive guess, so I would check wiring and common things first.