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Mark, ASE Certified Technician
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2003 buick lesabre Limited: The cooling fan does not work

Resolved Question:

I have a 2003 Buick Lasabere Limited. The cooling fan does not work. If you turn on the A/C is does work. All relays and fuzes have been checked and are good, also have replaced engine temp sensor. I had a guy hook on a scanner and he could manually turn them on. Is the computer bad? I have also been told that this car has two computers, which one would it be and where is it located?
Submitted: 3 years ago.
Category: Buick
Expert:  Mark replied 3 years ago.
Greetings and welcome to Just Answer. My name is Mark.

What is your problem that leads to you thinking your cooling fans do not work?
Customer: replied 3 years ago.
If you leave the car sit and idle at the grocery store the car gets hot. have seen the temp read 227 degrees and I turned it off and the fans did not come on. as long as you're driving the car the car has no problem with getting hot If you turn on the A/C the temp will go back down to 197
Expert:  Mark replied 3 years ago.
You cannot go by what is reading on your temperature gauge. The cooling fans are designed to come on at 223-227.

Keep in mind that water boils at 212. You can add 2 degrees for every pound on the cap. So a 16 lb radiator cap adds 32 degrees to 212. So now your water doesn't boil until 242. You then can raise the boiling point up even further because you have coolant and not just water. It is said the coolant usually doesn't boil until about 265-270.

If the cooling fans come on when you turn the AC on, then all the circuits and controls are in working order. You ground path, through the computer is working. You fuses and relays are working. If you can turn on the fans with the scanner, then again, the cooling fan circuit is intact.

The REAL way to diagnosis this is to have a scanner hooked up and see what the coolant temperature ACTUALLY is. Let the engine idle and watch the temperature. See what the temperature is that the computer is seeing. The cooling sensor is in the lower intake manifold just below the thermostat. Using the scanner, we can see what temperature the computer is reading.

You gauge on the dash is not always totally accurate.There's a good chance your engine is reaching the temperature that is actually being displayed. If your engine is not "over-heating" .... or the "red" temperature light coming on.....or your not "boiling" out the coolant.......I suspect you don't have an issue.

Below is a cooling fan description as outlined with-in GM. As far as your comment about your car have 2 computers, let me say you have more than just 2 computers. But the computers are responsible for other components. You have a "body" computer. You have a "transmission" computer. You have a "brake" computer. And of course your engine has it's own computer.

Cooling System Description and Operation

Cooling Fan Control

The engine cooling fan system consists of two electrical cooling fans and three fan relays. The relays are arranged in a series/parallel configuration that allows the powertrain control module (PCM) to operate both fans together at low or high speeds. The cooling fans and fan relays receive battery positive voltage from the underhood fuse block. The ground path is provided at G103.

 

During low speed operation, the PCM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. This energizes the cooling fan 1 relay coil, closes the relay contacts, and supplies battery positive voltage from the cool fan 1 fuse through the cooling fan motor supply voltage circuit to the right cooling fan. The ground path for the right cooling fan is through the cooling fan s/p relay and the left cooling fan. The result is a series circuit with both fans running at low speed.

 

During high speed operation the PCM supplies the ground path for the cooling fan 1 relay through the low speed cooling fan relay control circuit. After a 3-second delay, the PCM supplies a ground path for the cooling fan 2 relay and the cooling fan s/p relay through the high speed cooling fan relay control circuit. This energizes the cooling fan s/p relay coil, closes the relay contacts, and provides a ground path for the right cooling fan.

 

At the same time the cooling fan 2 relay coil is energized closing the relay contacts and provides battery positive voltage from the cool fan 2 fuse on the cooling fan motor supply voltage circuit to the left cooling fan. During high speed fan operation, both engine cooling fans have there own ground path. The result is a parallel circuit with both fans running at high speed.

 

The PCM commands the low speed fans ON under the following conditions:

The engine coolant temperature exceeds approximately 106°C (223°F).
The A/C refrigerant pressure exceeds 1310 kpa (190 psi).
After the vehicle is shut OFF, the engine coolant temperature is greater than 118°C (244°F) and the system voltage is more than 12 volts. The fans will stay on for approximately 3 minutes.

The PCM commands the high speed fans ON under the following conditions:

The engine coolant temperature reaches 112°C (234°F).
The A/C refrigerant pressure exceeds 1634 kpa (237 psi).
Mark, ASE Certified Technician
Category: Buick
Satisfied Customers: 841
Experience: 34+ yrs Dealership Exp. - Fully State & ASE Certified - GM Master & GM World Class Tech
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