Need Help!!...My 2008 base,auto overheated yesterday went to 268 degrees.Has new water pump and thermostat. I read some old post and one said to disconnect the coolant temp sensor and the fan should come on,well i did that and the fan did not come on? The connecter to the fan controller looks fine..I also put in a new temperature sensor about six months ago.I watched a video and to get to the fan connecter he jacked up the car to get to it...I turned 81 on the 7th of August and i no longer can do much The fuse checked ok with my meter....Did not see a relay. Thanks for anymore help.......Ken

 

There’s no relay. There’s a fan controller attached to the shroud that is responsible for fan speed and it’s also in the circuit to supply power to the fan. But the connector looking OK doesn’t mean it is. If the fan isn’t running ever, the contacts could still be melted or arced inside. You need to disconnect it and check the condition of the pins and sockets as a start.

 

Definitely unplug it and check. They could be melted inside. Same thing happened to my 2008 Z06, and I just cut out that connector and direct soldered the connections.

 

I will do that...Thank you sir

 

Did you have to do it from under your vette?

 

My fan plug melted while I was on a road trip. Made it to Walmart to buy a floor jack and jack stand but didn't need as I was able to pull the right side up on a curb which got car high enough to work from underneath. I recall the harness was fairly lengthy so was able to unclip it from the shroud and pull down far enough to easily do the 10 gauge wire bypass.

Sounds like you need a test light to probe for power before and after the plug and at the fan.

Cooling Fan Inoperative
Circuit/System Description
The engine cooling fan is a variable speed fan. The engine control module (ECM) controls the fan speed by sending a pulse width modulated signal to the cooling fan speed control module. The cooling fan control module varies the voltage drop across the engine cooling fan motor in relation to the pulse width modulated signal. The cooling fan speed is affected by many different conditions and can be adjusted from 10-90 percent duty cycle. Ninety percent is considered high fan speed. When multiple cooling speed requests are received, the ECM uses the highest cooling fan speed of all the requests. During normal fan ON operation, the control circuit voltage will be low and near battery voltage when the fan is OFF.

Circuit/System Testing
Important: The Circuit/System Verification must be performed first or misdiagnosis may result.

Ignition OFF, disconnect the connector from the cooling fan speed control module.
Ignition OFF, install a test lamp between the cooling fan speed control circuit terminal 6 and B+. The lamp should be OFF.
⇒ If the lamp is ON, test the cooling fan speed control circuit for a short to ground. If the circuit tests normal, replace the ECM.

Ignition ON, command the cooling fan speed from 0-100 percent with a scan tool. The brightness of the lamp should change with the commanded states.
⇒ If the lamp brightness does not change correctly, test the cooling fan speed control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.

Ignition OFF, measure between the cooling fan speed control module ground circuit terminal 2 at the harness connector and ground for less than 1 ohm of resistance.
⇒ If greater than the specified range, repair the module ground circuit for open/high resistance.

Ignition OFF, verify that a test lamp illuminates between the B+ circuit terminal 3 and ground.
⇒ If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.

Install appropriately fused jumpers between the cooling fan harness connector terminals 1 and 4 power and ground. The cooling fan should activate at full speed.
⇒ If the cooling fan does not activate, replace the cooling fan.

If the ECM, fan, and all circuits test normal, replace the cooling fan speed control module.

 

Take the car to a diagnostic shop and not a general repair shop or a dealership…you said you can’t do much so don’t hurt yourself.

 

Ken, one easy thing you should check first. Make sure the fan can easily rotate. Wouldn’t be the first time some road debris got sucked up in there and jammed the fan. A plastic bag will do it nicely.

 

Check thc 60 amp fuse in fuse box. Pull it out there have been know issues it melting the connector there too. Also check fuse.

 

Did that and it is ok.Thanks

 

You have a new water pump and thermostat…. Did it start overheating immediately after you replaced or was it fine for a while?

Id be suspicious of the thermostat and also of air pockets. Bleeding these cooling systems can be tough.

I am also 99% sure that if you turn your ac on it should force the fan to turn on.

 

The idea that turning on the AC forces the fan on is a myth. Attached is a GM document that describes the operation of the cooling system. There are a number of factors that determine if/when/at what duty cycle the fan runs. The whole idea is to run the fan at an appropriately speed and only when needed.

 

I tend to agree with the fans not coming on when A/C is enabled. I posted years ago about the fans coming on automatically with the A/C (this happens in most cars), and was told the same thing, that it isn't always the case!!

 

If you look at the inputs that activate the cooling fan seeing 160 psi from the AC Pressure Sensor will usually occur around 60-65 degrees if the system is charged properly…if it’s 60 degrees or lower you won’t be seeing 160 psi but who turns their AC on at 60 degrees…now when you start the car and the AC is on the cooling fan will run at low speed but if you remove the AC pressure sensor connector the fan will stop.

 

Op - I’m a little unclear. When it overheated, was the fan not running or do you know?

there is focus on the fan but when it was running and overheating, did you see the fan not running?

if you are sure the fan wasn’t working, then there are things to check (for example, the connector on the little box on the fan tends to overheat and fail on our cars)

but if all you know is that it overheated, there are other things we can check.

One of the first places to look would be the fan, as the connector is a known problem and that would cause these issues.

However, you mentioned two new parts; if the problem happened immediately after installing these parts, THAT is where I would focus. With that said, I would first make sure the fan will run because that’s pretty quick and easy.


if the problem happened immediately after this work was done, maybe a fan connector was overlooked. Maybe there is an air bubble. Maybe the thermostat is bad.

there are things you’ll have to start looking at.

 

The only corvette shop is 150 miles northeast of me.I'm gonna call a mobile mechanic that i have used before and he knows what he is doing. Thank You very much for your reply.

 

So you’re cruising at highway speeds, you turn on the AC, and the fan comes on? I don’t think so. The conditions as described in the document need to be met. It’s not like the AC button is an on/off switch for the fan. It’s not a reliable test of the rad fan.

 

Yes, the cooling fan will come on when you turn the AC on…read your PDF !!…as long as the high side pressure is above 160 psi it will run at a lower speed until the outside temp increases and the high side pressure normally increases…if all of the other conditions such as coolant temp etc are not met the fan will not run if the high side pressure is less than 160 psi if for instance you have a low charge…start your car when it’s dead cold and you’ll see the fan run at low speed…now remove the AC Pressure Sensor connector if you know where that is and the fan will stop.

 

The same thing happened last year and it was after dark,i pulled over in a parking lot and shut down the engine and lifted the hood and the fan was running at a very high speed for a few minutes like it should as i have read about to cool the engine down.That is when i had a new oem water pump,thermostat and new belt put on and all was good until 8/7 (My birthday).I went to renew my driver license at the DMV and it was hotter than hell out"113 degrees".I drove abou 3 miles and i temps started to climb very fast and i can not hear my fan running from inside the car,due to very loud exhaust.I pulled over and shut the engine off and lifted the hood and the fan was not running like it should of been,and i was getting all kinds of readouts in the DIC.It pooped out a good amount of my coolant mix.I was letting it cool down and a guy stopped and he had a gallon of good water and i added water and i was only two blocks from home.About 50' from home it shut down some of the injectors like it should.I pulled into the car port and let it cool down for a couple of hours,added more water and started it up and when my temp gets to 195 my fan should come on at 30% and 70% at 203,well that did not happen..First thing i did was to check the fuse with my meter it was good.More Later

 

It does NOT have to be a Corvette shop…a mechanic well versed in electrical diagnostics which may be only 1 in a 100 or more and will be able to diagnose this …Corvettes don’t have magical electrical systems !!…I can diagnose anything electrical on a Corvette or on a Honda…if you know how a solenoid, thermistor, or a potentiometer operate they ALL basically operate the same way…if you have an auto electric shop in your area take it there.