Originally you were saying only one fan was coming on. Do you now think both fans are coming on? Have you verified the two fan fuses are good?

 

I would check fuse 14.

 

I believe they are both coming on only on low speed,
I swapped the 2 relays (3604 and 7234) and high speed fans came on briefly and went off, this is getting frustrating

 

14 10 amp, I replaced it even tho it wasn’t burned, no change

 

I agree with toys4life on the 160 thermo not being needed. Aside from what others have said, you need to ensure you have the stock air damn under the front end pushing air into the rad area. I am assuming your car is stock and no aftermarket splitters are in use, correct? I ask as some of these cause cooling issues. Make sure coolent level is correct and no leaks exist. These rads start to leak at the seams where the plastic end tanks meet the aluminium. Just the basics before you start worrying about fans, but as you mentioned it's hot while driving..

 

Yes the car is all stock

 

If you confirm that both fans are coming on, that confirms both fans are in working order. The only reason they would work in low speed mode and not go into high speed mode is that the PCM is not commanding them to run in high speed mode. As mentioned above the temperature limits to enter high speed mode are really high, though I don't have my FSM handy today to confirm the 236°F figure shared by another poster. It sounds correct to me. If you're saying the temp hit 235 at a light and the fans didn't ramp up then I'm not surprised because 235 != 236.

From my perspective the fan controls seem to be working as designed. If you have these temp issues on a 70 degree night especially while moving, I can virtually gaurantee your condenser is packed full of sand and junk and you need to clean it out. The bottom line is on a 70 degree night the fans shouldn't need to come on because the temp sitting at a light shouldn't exceed 220 unless the radiator is compromised. I live in SC the armpit of the USA where temps have been in the mid 90s for 2 months straight with high humidity and my fans hardly come on at all because I painstakingly cleaned my radiator 2 years ago after I had similar symptoms.

 

I'd like to give you, and others, a little idea I had, and it worked pretty well, if I do say so myself, and I do!! Here's what I did........

Many air nozzles/blow guns have a threaded tip. Mine does, so I unscrewed it. Mine has a thread very close to a 1/8 NPT. So I bought a 2 foot length of 1/8 pipe, then had it threaded on both ends. I screwed 1 end into my air nozzle, and screwed a street elbow onto the other. Then I pulled my upper radiator mount that locates the radiator AND A/C condensor. After removing this piece you will note there is about a 2 inch gap between the front of the radiator, and the back of the condensor. CAREFULLY. VERY CAREFULLY, lower your 2ft length of nozzle extension down this gap, with the open end of the street elbow pointing to the front of the car/back of the condensor. When you pull the trigger on 90-120lbs of air pressure, you will be AMAZED at the bugs, dirt, and general garbage that comes out of your condensor!!! As a side note......Is your A/C working correctly? If I'd want to gamble, I'd say it's not working very well. The reason I said to lower your nozzle extension carefully is because it's pretty easy to start wacking against the fins, which will defeat your intentions if you screw up enough of them. Good luck

 

Replaced all 3 relays, checked all fuses, cleaned radiator, only low speed fans are coming on even with the A/C on. This is a real head scratcher

 

I would check to see if you have 12 volts at fuses #14 and #46. If they’re good then check if you are getting 12 volts downstream at relays #43 and #44. If they’re good. I would jump relay #44 & #45, this will put the left fan into high speed. Jumping Relay # 43 will put the right fan into high speed.

 

C5 Cooling Fans Description and Operation

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 and ignition 1 voltage from the underhood electrical center. The ground path is provided at G102.

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 through the cooling fan motor supply voltage circuit to the left cooling fan. The ground path for the left cooling fan is through the cooling fan 3 relay and the right 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 3 relay through the high speed cooling fan relay control circuit. This energizes the cooling fan 3 relay coil, closes the relay contacts, and provides a ground path for the left cooling fan. At the same time the cooling fan 2 relay coil is energized closing the relay contacts and provides battery positive voltage on the cooling fan motor supply voltage circuit to the right 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 low speed cooling fan is commanded on when the coolant temperature reaches 108°C (226°F). It is turned off if the coolant temperature lowers to 104°C (219°F). The high speed cooling fan is commanded on when the coolant temperature reaches 113°C (235°F). It is turned off if the coolant temperature lowers to 108°C (226°F). When the A/C is on and the coolant temperature reaches 85°C (185°F), the low speed cooling fan will be turned on at vehicle speeds less than 56 kPh (35 mph).

Knowing all of this, I would short the DK BLU wire to ground with the ignition ON. This should force the high speed fans on. If they don't come on, I would first check to see that you are getting voltage at both fuse 14 and 46 and, if you are, I would then trace back the DK BLU wire to the PCM and hope you find an issue with the wiring. I am hoping it is not a PCM problem but a connection issue. It is also possible that you could have a really bad ground at G102 that only supports the current flow at low speed fan operation and does not allow the current needed for high speed operation. It is an easy check and one way to verify if this is the problem would be to short the DK BLU wire and then check the G102 ground connection by loosening and wiggling it back and forth to see if making better contact increases the fan speed.
G102 is located by the passenger headlight.

 

this is very helpful

 

Also read this thread: https://www.corvetteforum.com/forums...an-issues.html
Similar issue and interesting conclusion - burnt fuse box. Using aftermarket fans though and might not produce the same results with OEM. Diagrams show what I wrote above about how the fans work.

 

Wow this is very similar to what I have going on! Although I never replaced my fan

 

confirmed fans come on when jumped, I believe the only thing it could be at this point is PCM

 

Hopefully it is only corrosion at the plug but if it is you still might have to swap out the PCM. Let us know what you find/figure out.

David

 

Pcm removed, no corrosion at harness, will order pcm and see if that fixes it

 

Man, what a lot of brainpower to help this guy diagnose and hopefully fix his issue! Impressive!

Nice going Corvette Forum!!

 

Everybody has been very helpful, This has been a real pain to diagnose

 

Yikes ordering a PCM to fix a cooling issue... did you verify the signal for the fan relays isn't coming on? This sounds like a highly unlikely root cause. The PCM hardware is robust and not really known for randomly blowing outputs.