Check engine light comes on. diagnostic test

It could be the fuse, the relay or the fan motor. Start by checking the fuse and if it's good swap the relay with one with the same number if the fan doesn't run unplug it and use a test light to check for current if the test light lights the fan motor is bad. I hope this helps. Take care.

threw a po128 ??? Doesn't throw code's ,it stores code's . P0128 code does not tell you to replace the sensor either . With every code comes a diagnostic test procedure listed in a factory info. manual .
DTC P0128: Engine Coolant Temperature (ECT) Below Thermostat Regulating Temperature
The purpose of this diagnostic is to analyze the performance of the thermostat, by using the ECT sensor to determine if the engine coolant will increase at the correct rate, and also meet the calibrated target temperatures under various operating conditions. The ECM uses the start-up ECT and the start-up intake air temperature (IAT) to begin the diagnostic calculation. The air flow into the engine is accumulated, and vehicle speed, distance, and engine run time are also factored in to determine if the ECT does increase normally and reach the calibrated target temperatures.
Diagnostic Aids
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DTC P0128 occurring with insufficient vehicle interior heating is an indication of improper thermostat operation.

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Corrosion in the ECT sensor terminals or the ECT harness connector results in a greater voltage on the ECT sensor signal circuit, which is interpreted by the ECM as a colder ECT.

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A slight to moderate resistance in the ECT sensor signal circuit or low reference circuit will affect this diagnostic. This condition results in a greater voltage on the ECT sensor signal circuit, which is interpreted by the ECM as a colder ECT.

Circuit/System Verification

1. Ignition OFF, inspect the cooling system surge tank for the proper coolant level. Refer to Cooling System Leak Testing and Cooling System Draining and Filling .
2. Ignition OFF for 8 hours or greater.
3. Ignition ON, observe the scan tool ECT Sensor and IAT Sensor parameters. The ECT, IAT and ambient temperatures should be within 15?°C (27?°F) of each other.
Important: A critical analysis of the operation of the thermostat is necessary to properly diagnose this DTC.

4. Verify the proper heat range, and the operation of the thermostat. Refer to Thermostat Diagnosis .
5. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the ECT sensor.
2. Ignition OFF for 90 seconds, test for less than 5 ohms between the low reference circuit terminal B and ground.
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If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

3. Ignition ON, verify the scan tool ECT Sensor parameter is colder than -39?°C (-38?°F).
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If warmer than the specified range, test the signal circuit terminal A for a short to ground. If the circuit tests normal, replace the ECM.

4. Install a 3A fused jumper wire between the signal circuit terminal A and the low reference circuit terminal B. Verify the scan tool ECT Sensor parameter is warmer than 149?°C (300?°F).
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If colder than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.

5. If the circuits test normal, test or replace the ECT sensor.

Hi there,

Diagnostic codes # P0115 to P0119 all relate to the ECT (Engine Coolant Temp) sensor circuit.

Assuming you have correctly diagnosed a faulty ECT sensor, here are the instructions to locate and test:

* Look for a bolt size sensor with a wire attached - on Mitsubishis, the ECT sensor is usually located either on the Intake Manifold, or close to the Thermostat housing (to measuer coolant temp).

This is what is looks like:


* To test the ECT sensor:

* With the sensor portion immersed in hot water, check resistance as per the table below (convert to degrees F if necessary):


* If the resistance is too far out of spec, then replace the sensor.


Cheers,


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2.4 ENGINE COOLANT SENSOR IS LOCATED ON THERMOSTAT HOUSING THE 3.3 AND 3.8 ENGINE COOLANT TEMPERATURE SENSOR IS LOCATED LOWER INTAKE MANIFOLD.ALSO CHECK COOLANT FAN FUSE AND RELAY.FUSES RELAYS LOCATED LEFT SIDE OF THE ENGINE COMPARTMENT.

The temperature sensor is located on the intake manifold by the thermostat housing. Check the wire leads first and if that's good, replace the sensor and thermostat. The 4.3 was programed by the factory to run it's best at 190'", if it runs too cold. The mil light comes on indicating a temperature sensor failure.

Leave 02 sensor alone ,it is doing it's job . It is heated up because of lean fuel mixture due to incorrect engine temp.,replace thermostat before looking further.

The only real way to tell why the check engine light is on is to run an engine diagnostic scan which will pinpoint exact problem location. Many part stores will test it for free. Most shops charge $40 which is well worth it. It is likely a sensor or circuit that is faulty.

How to Replace a Throttle Position Sensor
(DIY & Save up to $135.75 ) - Time: 2.1 hours

Parts:
1. Throttle Position Sensor - $ 55.44

Tools:
1. Scan Tool
2. Screwdriver
3. Multimeter

Procedure:
1. Locate the OBD data link connector (DLC). Refer to your owner’s manual for the specific location.

• Tip: The OBD-I data link connector is usually located in the engine compartment near the battery or the fuse box. The OBD-II connector (post 1995 cars) is usually located beneath the instument panel next to the steering column.

2. Turn your key to the“ON” position. Do not start the engine.

3. Plug your scan tool into the OBD data link connector. Turn on the scan tool and select the appropriate steps to read the diagnostic trouble code (DTC).

Scanner plugged into OBD-II data link connector.

• Tip: The OBD-II diagnostic trouble code (DTC) is a 5 character alphanumeric code. The first digit is a letter that indicates the component group, the second digit is OBD mandated or manufacturer specfic, the third digit is a subgroup, and the fourth and fifth digits define the component and basic problem.
  

• 4. Locate the throttle position sensor.

• 
  
• Throttle position sensor
  

• 5. Disconnect the electrical connector from the throttle position sensor.

• 
  
• Electrical connector removed
  

6. Test the resistance of the throttle position sensor (TPS) with a digital multi-meter. If the resistance is out of specifications, the TPS must be replaced.

• 7. Remove the throttle position sensor.



Removing sensor mounting screws

8. Install the new throttle position sensor. Tighten the mounting screws and attach the electrical connector.

• 9. Erase the diagnostic trouble code (DTC) with the scan tool using the“delete” or“erase” command. Road test your vehicle to see if the check engine light returns.

Check engine light


• Tip: If the check engine light returns, repeat the diagnostic process for additional DTCs or take your vehicle to a certified repair shop.

Direct OE replacement

Hope helped with this. Good luck (remember rated this help).

The temperature sensor is located by the thermostat housing, it has two wiring coming out of it. The top unplugs and the bottom which is the sensor unscrews.

The water temp sensor is located near the thermostat housing. This sensor is what tells the ECM to turn the fan on/off. The water temp sending unit is located near the same area. You know you have the correct sensor is because the water temp sensor has a 2 prong plug. The water temp sending unit only has 1 prong.