2001 Chevy Cavalier Coupe. 2.2 4cyl.
Check Engine Light codes  P0128.
Repair done prior = A year ago hired a mechanic to supposedly change thermostat due to
overheating engine. Done to repair = Went to Autozone and got the
code P0128. Sales associate
suggested i change the thermostat so i purchased one and   "replaced" it today. Also just found out
today that the mechanic hired last year to replace old thermostat never put in a new one. No wonder
during the winter months i had no heat...
Question = My check engine light came on about 1 week ago. I brought it to AutoZone and they gave
me a Code P0128. Probable causes: Check Coolant Level - checked and ok Thermostat Defective -
put a new one in today ECT Sensor Defective - No replacement part available at AutoZone.

After placing the new thermostat in place and filling the reservoir with fresh antifreeze (50/50
Dexcool), I turned on the ignition and then noticed the engine temperature gauge raised up too fast
just past the halfway point in a matter of minutes. Check engine light still on.

It is possible the sensor is bad, or you have air in the cooling system. This  code normally comes on
because the engine coolant temp has not reached normal operating temp within a per-determined
time. Air pockets around the sensor will cause it to not read properly. Suggest replacing the sensor
and bleeding the system.
what about replacing the thermostat? That is a quick and easy repair.

2001 Chevy Impala coolant fan keeps running after the engine is off. The temperature gauge quit
working at the same time. Any suggestions? Thanks,Candy

if you are referring to the radiator fan, it sounds like you are describing a pretty common problem. I'll
bet the check engine light is on also. If it is then you probably have a trouble codes stored – P0128.
This code is described as "coolant temperature below thermostat threshold". Basically the thermostat is
stuck open and the engine is not getting to operating temperature. That's why the gauge looks like it
quit working but is just showing cold coolant temperature. The fan staying on is the computer going into
sort of a safe mode. Since it does not know what temperature the coolant is, it turns the fan on in case
it's too hot, to prevent the engine from overheating. Get the thermostat replaced, the code cleared,
and you will be good to go. This is assuming that your antifreeze is not low. If it were low you have the
same problems as above. So check that first.
Check your fuses too
I was at my wits end because of my 2.2 Cavalier overheating.I tried everything short of a
water pump and head gasket but then read on a forum to move the thermostat back to the
upper part of engine like on the older cavaliers.I put a gasket in the lower housing and on
the upper I cut off the cone inside the housing and filled it flat installed my thermostat and
gasket refilled coolant and have never had another problem.
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2001 Chevy Cavalier P0128