1. Diagnose the Problem:
* Check the Coolant Level: Low coolant can cause inaccurate readings. Top off the coolant if needed, using the correct 50/50 mix of coolant and distilled water (check your owner's manual). Let the engine cool completely before doing this.
* Inspect the Coolant Temperature Sensor (CTS): Locate the CTS (usually on the engine block near the thermostat housing). Visually inspect it for any damage, loose wiring, or corrosion. Pay close attention to the connector.
* Check Wiring and Connector: Carefully examine the wiring harness leading to the CTS for any breaks, shorts, or chafing against engine components. The connector itself should be clean and securely connected.
* Test the Coolant Temperature Sensor (CTS): This requires a multimeter. You'll need to consult a repair manual specific to your 2001 Chevy Impala to find the correct testing procedure and resistance values for the CTS at different temperatures. This is the most critical step to determine if the sensor is faulty. A bad sensor will often show incorrect resistance values compared to the specifications in your repair manual. There are many online resources and YouTube videos demonstrating how to test a CTS.
* Check the Thermostat: A stuck closed thermostat can cause the engine to overheat and lead to inaccurate CTS readings. While not directly related to the P0128 code, a malfunctioning thermostat could contribute to the problem. Observe the engine's temperature gauge and feel the upper radiator hose after the engine has run for a while. A stone cold upper radiator hose while the engine is hot indicates a stuck closed thermostat.
2. Repairing the Problem:
Based on your diagnostic findings, the repair could involve:
* Replacing the Coolant Temperature Sensor (CTS): If the CTS test reveals it's faulty, replace it with a new one from a reputable auto parts store. Ensure you get the correct sensor for your specific engine. This is usually a relatively easy repair.
* Repairing Wiring: If you find any damaged wiring, you'll need to repair or replace the affected sections. This might involve splicing in new wire or replacing portions of the harness.
* Replacing the Thermostat: If your thermostat is stuck closed, replace it.
* Clearing the Code: After making any repairs, clear the trouble code using an OBD-II scanner. Run the engine for a while to ensure the code doesn't return.
Important Considerations:
* Repair Manual: A repair manual specific to your 2001 Chevy Impala is highly recommended. It will provide detailed diagrams, specifications, and procedures for testing and replacing components.
* Safety: Always allow the engine to cool completely before working on it. Be cautious when working with coolant, as it can be corrosive.
* Professional Help: If you're not comfortable performing these repairs yourself, take your Impala to a qualified mechanic.
By systematically following these steps, you should be able to diagnose and repair the P0128 code on your 2001 Chevrolet Impala. Remember to always prioritize safety and consult a repair manual for specific instructions related to your vehicle.
