Vehicle Is Overheating

The Problem noticed on 1999 Pontiac Sunbird.The vehicle overheats and Cooling fan not turning ON.
But when the Obd code scanner is connected to DTC port the fan comes ON and when OBD code scanner is disconnected the Fan Turns off and will not turn ON.

WHY FAN TURNS ON WHEN ERROR CODE SCANNER IS CONNECTED?


The cooling  fan operating system is pretty simple. You scanning it, and the fan coming on tells you the ECM is turning on the relay when requested. So we know that the Relay, and ECM command CKT to the relay {Dk Green/White wire} is engaging the relay.That is why Fan is accepting the voltage from relay and Turning ON.

SEE THE FAN WIRING DIAGRAM AND OTHER PARTS WIRING THAT MAKE THE FAN OPERATE


SO WHAT DO YOU THINK THE PROBLEM IS?

Coolant temperature sensor and its signal to ECM needs to be inspected.
It seems that coolant temperature signal voltage is high.

You have to verify the coolant Temp Sensor is sending proper info to the ECM. If the DATA stream on the scanner reads 226 to 230 degrees, and the fan does not come on, then you know the sensor is operational, and the ECM is not processing the info correctly.
This is common issue noticed many a times at our garage.The Fan gets inoperative due to faulty ECM.

SO WHAT IS FAULTY COOLANT TEMPERATURE SENSOR OR ECM?

To confirm that testing is required.I have already provided you the wiring diagram.That will help you the most to confirm what is faulty as per voltage test.


In the the diagram I attached above, you see the yellow and black wires to the Temp Sender. You need to verify that you have a good ground on the Black wire, and 5 Volts on the yellow. If you do, jumper the pins. If the fan comes on, replace the sensor. If not, chances are the ECM is bad.

WHAT IS MOST POSSIBLE OUT OF ECM OR SENSOR?

As per you description i assume its faulty ECM.

The fact that the Fan came on with the code checker installed, this puts the system in "Field Service Mode" and will have the ECM turn on relays, so we can assume that the ECM has an internal issue if the Sensor and it's CKT's are good.

This will help.

Thanks.

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Engine Overheats while Driving?

The problem is Engine overheating while driving.Its noticed towards engine compartment.

In that case there are few car parts,that are to be inspected and tested.
Inspect this parts and confirm what is causing the problem.

Leaking Raditor Hose.
Leaking Head Gasket.
Thermostat Stuck Closed.
Worn or Damaged Raditor Cap.
Radiator Fins Obstructed.
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Heater Core May Be Leaking Antifreeze/Coolant into The Vehicles Floor Area.
Intake Manifold Gasket Leaking, Worn, or Damaged Intake Manifold Gasket.
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Faulty Raditor Cooling Fan Motor.

Any of the components out this can cause engine overheat issue while driving.


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This details will help.

Thanks.

Car freeze overnight and started overheating while driving?

Yes this occurs many a times,The car sits overnight in cold nights and engine gets freezed and in the morning while driving it overheats.

Did you check the freeze level of the coolant? Only two things can cause the heater stopped working in these are related to know coolant flow. The first one is the coolant itself is low and are air pockets so the coolant does not circulate through the heater core. Second would be is if the freeze level is not low enough. The heater core may have frozen. You need to make sure that you have the proper amount of coolant and that there are no air pockets. Start the vehicle with the radiator cap off and continually add coolant as you hold the engine RPM at 2000 RPM with the heater in the full hot position. 

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When any of the engine cooling system components and parts gets weak or stops working,the overheating will be noticed.
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It can be plugged/clogged radiator problem.It can be issue with water pump leaking or faulty catalytic converter.
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