On the 2005 Chevy Colorado, the P0128 is pointing to a fault in the Cooling System. Basically it’s saying that the on-board computer isn’t seeing the Coolant getting to the temp that it should be in a pre-determined amount of time. There are a couple of things that can set this code; a stuck Thermostat or a faulty ECT sensor. Most commonly on this vehicle, the ECT. Best place to start is by inspecting the ECT electrical connector and harness for any loose, broken or damaged wires. If the visual inspection checks ok, the ECT and Thermostat should be tested and replaced as necessary. To replace the Coolant Temp Sensor you will require a special tool: Coolant Temp Sensor Socket. You can usually rent this tool from most local “big chain” parts stores.
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