Engine overheating

Tiny
6STEELRINGS
  • MEMBER
  • 2003 PONTIAC GRANDVILLE
  • 3.1L
  • V6
  • 2WD
  • AUTOMATIC
  • 185,000 MILES
Half of the neck of my radiator broke off as I pulled in to yard and the temperature was at 230 which the max in red is 260. So I reattached it and put coolant in it and got into my garage. I changed the radiator and bled the two air bleeds and the car warmed to normal 195 but then as it got to 215 the fans would not come on! I let it warm to 230 and they never came on and it was creeping up so I turned on A/C switch and the fans came on temperature stayed normal at 195! I turned off A/C fans would turn off and temperature would creep up again so I then changed, the black fan relay and some thing happened! I then changed the coolant sensor and same thing happen, they would not come on until I turned A/C on! The book said only thing left was ECM so we got a nice one and changed it and the car was idling very nice, and we drove around and the temperature stayed normal at 195 we pulled into yard and the fans came on like the should at about 210-215! We were excited problem solved. Next day 4/7/2020, I drove to bank and PO and the car ran really good but the check engine light came on but the temperature held good at 195 it was a cool day. I pulled in and popped hood and let it idle to make sure fans would operate properly and the darn fans would not come on. I turn it off and coded the ECM and the reading was PO135 02 sensor #1, so we changed it thinking that might have something to do with it but the fans still did not come on. Then I read a post by a tech on here said to turn car on, engine off and pull plug off coolant sensor and the fans should come on I did this and the fans did not come on, so is there a short in the wiring? Is that the reason fans did not operate when I did the unplug technique? Because prior to doing that we were hearing a hiss or low crackling sound when we would turn off the car after having it idling! The wires off the sensor run under the air charger housing I think is what it is looks it is attached to the intake manifold or it is part of the intake manifold. Look like only way to get to the wires. Please advise!
Wednesday, April 8th, 2020 AT 5:09 PM

47 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good evening,

First, when the A/C is on, the fans should come on. That is normal.

What is not normal is the fans not working when you disconnect the coolant sensor.

https://www.2carpros.com/articles/how-an-electric-cooling-fan-works

One thing I would do is replace the thermostat as I never saw anything about it being replaced.

https://www.2carpros.com/articles/replace-thermostat

Beyond that, check the fuses in the diagram I attached for power on both sides to be sure they will send power to the fans.

https://www.2carpros.com/articles/how-to-check-a-car-fuse

https://www.2carpros.com/articles/how-to-check-wiring

Roy
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Wednesday, April 8th, 2020 AT 5:29 PM
Tiny
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Can't see how thermostat could not allow fans to come on, I told you it reaches perfect temperature 195 and as long as its a cool day and you keep moving it stays right there. If thermostat is stuck closed the temperature will rise and the fans should come on and that wouldn't make a difference if the fans are on because the thermostat is stuck closed it will overheat with fans running cause the cooled radiator water will not get into the block. Then I would immediately know it was a stuck closed thermostat! If its a sticking thermostat that sticks open, wouldn't driving it eventually push the temperature over the thermostat rating and kick the fans on? Look on a warmer day the air flow around the radiator keeps it cool as long as you are moving consistently but when I got in area of a few stop signs it would start to climb until I got into an area with more moving time between slow downs or stops. Even if you remove the thermostat from a vehicle, where there is not thermostat, it will still eventually overheat if the fan or fans do not come on. Why didn't the fans come on that test where I turn the key on but engine off and pulled the temperature sensor wire off? You guys said that the fans would come on. What would cause them to not come on? Could it be a shorted wire on that sensor circuit?
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Wednesday, April 8th, 2020 AT 7:55 PM
Tiny
ASEMASTER6371
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That is why I posted the wiring diagram. You need to check the fuses for power on both sides.

There are 2 relays for the system. We need to start somewhere and that is where we start.

Roy
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Wednesday, April 8th, 2020 AT 9:11 PM
Tiny
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Actually there are 3 relays one called Fan Relay, then cooling fan 1 relay then cooling fan 2 relay, this is what is said in the fuse relay center under the hood! The Fan Relay is black and has five prongs. I bought a new one of those and the problem still persisted. The other two relays are gray and have only four prongs on them.
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Wednesday, April 8th, 2020 AT 9:34 PM
Tiny
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I seem to have power on all fuses. My coolant sensor has 3 wires green, yellow and orange black. How do I test it and why didn’t my fans come when I unplugged the coolant sensor? Does the car need to be running when I unplug it. Or do I unplug it then start the car? Why does my sensor have three wires? Also what is engine control system and MAP sensor?
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Monday, April 13th, 2020 AT 10:56 AM
Tiny
ASEMASTER6371
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The coolant sensor should only have 2 wires. A 5 volt reference and a return to the ECM.

https://www.2carpros.com/articles/how-to-check-wiring

The map sensor is a 2 wire sensor and has no effect on the issue.

The coolant sensor is by the thermostat.

Roy
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Monday, April 13th, 2020 AT 11:07 AM
Tiny
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Because on my 2003 Grand Prix 3.1 liter engine it has 3 wires I assume the green is a ground.
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Monday, April 13th, 2020 AT 12:32 PM
Tiny
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Okay, I tested the wires on the coolant sensor. As I said the green was a ground and I got a good 12.5 volt reading there. I tested for system voltage to computer and got 4.95 volts. I left it unplugged and started the car and they did come on with sensor unplugged! I left car running and tested the return voltage voltage from computer and got.14 volts. So can you tell me what problem is now?
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Monday, April 13th, 2020 AT 12:42 PM
Tiny
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Here it is. I can send a picture of the connector if you want.
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Monday, April 13th, 2020 AT 1:20 PM
Tiny
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Here are the connector wires:
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Monday, April 13th, 2020 AT 1:25 PM
Tiny
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The proper temperature for this car is 195 and on a cooler day I can drive it around and as long as I got good air movement it stays there. But if you get in stop and go traffic or stuck in traffic temperature goes up and the darn fans won’t come on. So I have to turn the air on to get the fans on then temperature drops back normal.
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Monday, April 13th, 2020 AT 1:30 PM
Tiny
ASEMASTER6371
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Okay, that is the sensor that does both the temperature gauge and the signal for temperature.

I would change the thermostat as it may be opening late causing the temperature to go up. The position of the sensor makes a difference.

https://www.2carpros.com/articles/replace-thermostat

Roy
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Monday, April 13th, 2020 AT 1:41 PM
Tiny
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So are you saying that the green is to the temperature gauge not a ground? Because the orange with black stripe was the 4.9 volts to the computer and the yellow had the.17 volts which should be the return voltage from computer.
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Monday, April 13th, 2020 AT 4:21 PM
Tiny
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Well Roy, I believe I have a short in the return wire from the computer! I ran those test I told you I had the connector pulled off and the fans ran then I put it back on and my wife came home and she wanted to see the connector unplugged and the fans run so I disconnected it and showed her and the fans ran! I retested all fuses and they were good I retested all the relays all 3 clicked and tested good. So I plugged the connector back and the darn check engine light came on coding the coolant sensor I cleared the code cause it is a new sensor. I decided to do a short to ground test cause my tester has setting on it where it makes a sound if something hot is shorted to ground so I tested all three points of the plug the one that had system voltage the one you say goes to the temp gauge tested good, the one that had the 4.9 volts to the computer tested good but the one carrying the return from the computer made the gauge sound and made continuity to ground! This car has the wires in a covering and they are taped but they run the wires right under the upper air chamber that aluminum piece bolted on top of the intake manifold so there is a ton of heat under there and probably has burned through and shorts the return signal to ground ! The computer sends a good signal but it never reaches the sensor! I believe that’s the problem! Does that sound feasible?
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Monday, April 13th, 2020 AT 11:34 PM
Tiny
ASEMASTER6371
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Okay first of all, I told you that disconnecting the sensor and the fans running is normal. It is supposed to work that way.

When you disconnect the sensor, The ECM sees no return voltage to the ECM and it will turn on the fans.

There is nothing wrong with that.

The light should have come on when the sensor was disconnected. That again is normal.

There is nothing wrong with the wiring as when the fans came on, that tested all the wiring to the fans.

You need either a new sensor or a thermostat as I stated 3 times.

Roy
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Tuesday, April 14th, 2020 AT 3:14 AM
Tiny
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I installed a new sensor. So Roy you’re telling me that the thermostat sticking later on after the engine starts to overheat past 195 is causing the fans not to come on? This makes no sense to me I know I’m being a hard head with you but it’s a nightmare changing the thermostat on this car if the upper radiator hose is hot it means the coolant is flowing and the thermostat is open!
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Tuesday, April 14th, 2020 AT 10:53 AM
Tiny
ASEMASTER6371
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No, I did not say that at all. If the thermostat is partially open the engine will not be hot enough to run the fans or turn them on.

Is this another new sensor or the same new sensor from before?

Roy
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Tuesday, April 14th, 2020 AT 10:55 AM
Tiny
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It is same new one. But the temperature keeps climbing toward the danger zone I shut it off at 230 or so cause with a 195 thermostat they should come on about 210 or 215 latest. My upper radiator hose gets very hot properly so I know the thermostat is opened at 195 the proper temperature. The temperature keeps rising and the fans never come on. When I bled the air water was running out both set screws.
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Tuesday, April 14th, 2020 AT 11:05 AM
Tiny
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Yes the engine was running?
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Tuesday, April 14th, 2020 AT 11:29 AM
Tiny
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Well, I changed the thermostat as I refilled the radiator I had the bleeds open and filled the radiator completely. I put a little in reservoir tighten the cap and it does same thing! The car will not turn fans on at the proper time. So we found a video on YouTube where a guy bleeds this car will it is running he starts the heater then opens the bleeder at the thermostat. It still did not work the fans still will not come on. I been fixing my cars all my life I have never seen this happen. Any other suggestions?
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Monday, April 20th, 2020 AT 4:36 PM

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