C4 Corvette Cooling Fan

Today’s Zip Corvette technical question comes from Jim, who owns a 1990 Corvette:

I have a 1990 Corvette convertible with 350 and 6-speed that I can only drive when the weather is cool because I cannot get the cooling fan to run. The fan motor is good (works when voltage is applied) and I have replaced all of the temperature sensors and the cooling fan relay, but still no fan operation. What else could be preventing the fan from running?

Answer: Your Corvette’s main cooling fan is controlled by the PCM. The PCM sends a ground signal to the fan relay when it sees the desired temperature to run the fan has been met. You need to check the relay and make sure you are getting your battery 12V and ignition 12V when the key is on. With the key on, jump the ground wire in the relay. If the fan turns on, you have an issue in the PCM and it may be time for a rebuild. If it does not turn on, then your problem lies in the fan circuit between the relay and the fans.

42 thoughts on “Why won’t my C4 Corvette’s cooling fans turn on?

  1. I had the same problem with my 1984 Corvette. I replaced the sensors, switch and fan motor. The problem was the temperature sending unit.

  2. I had the same problem with my 1986 Corvette. I found out that I had a bad wire running from the battery cable.

    Nassau, Bahamas

  3. Excellent info, especially considering I am looking at getting a Corvette for my next car.

  4. Where exactly is the cooling fan sensor on a 1985 Corvette? Finding all kinds of similar units but they are not like the replacement we bought.

  5. The dealer replaced the fan motor and they come on at 225 degrees. The dealer says thats were the fans should come on but that is way to hot for me. We live in Florida, I am going to try a 160 degree thermostat, purple ice w/water and 1 gallon of 50/50, hopefully that will help. If any corvette owners know otherwise please let me know.

  6. Stephen,
    The factory fans do come on at 225, this cannot be lowered by a thermostat. If you want to lower the main fan temperature on a C4 Corvette it has to be done by either a chip in the ECM or programming on 1994-1996 Corvettes. You can also wire around to a switch. On 1984-1989 Corvettes with dual fans there is a temperature switch in the cylinder head that controls the front fan. Our 1984-1991 Low Temp Fan Switch Conversion Harness will allow you to wire an extra ground wire to the main fan relay. When the switch hits its preset temperature it will ground the relay and turn the fan on early.

  7. I have a C5 Corvette and the air conditioner does not kick in when the air button is pushed; the result is a blown fuse. Could it be that the clutch is not kicking in or is it some other control. What is the best way to test the AC compressor clutch on a C5 Corvette?

  8. C4 corvettes have a knack for sucking up plastic bags and newsprint pages up in front of the radiator….Rolling vacuum cleaners…Overheating may damage the fan motor. I suggest you rewire the motor(s) with a Hayden adjustable fan conrol unit…it will run 1 or 2 fans (Use beefy wiring) If you still blow the fuses replace the Corvettes fan motor. This is a whole lot less expensive than replacing the computer or several sensors and your problem might be solved. I live in the hot South Florida and have solved all my problems with a few hours work. If you desire to keep the Corvette original other suggestions on this site will do as well.

  9. What is the best spark plug to use in my 1988 C4 Corvette. I just replaced the intake gasket (dealer did it) and the miss I had seems to be worse. Dealer suggested plugs and wires? Any help?

  10. If the Corvette is stock, I would just use the original Corvette Spark Plugs, which is a AC-Delco FR5LS. The Champion spark plugs also work well, they are a RC14YC. If you want to step up to the Iridium spark plugs which is what comes in the newer model Corvettes, you could get a NGK part number 2685. As far as the spark plug wires, stick with the OEM wires from AC-Delco. I would not price shop, you will get what you pay for most of the time when it comes to Corvette Spark Plug Wires.

  11. 95 c4: fans come on when AC is on, temp stay about 194 drgrees, however seems not to come on when AC is off. Bought temp switch but havent installed. Does it plug into the front of motor just above the water pump?

    Read comments above about 225 temp and fan comes on, is that one or two fans. Any help or comments would be greatly appreciated. Thank you, Greg

  12. I need a wiper switch for my 84 Corvette that is mounted on the door panel. I’m having trouble finding one . Any suggestions?

  13. Hey friends. so I have a 1993 C4 and I noticed the same “problem” with the heat – my ac and heater does not work, and my passenger floor board is leaking fluid, its a weird fluid, I believe its anti-freeze…I’m not sure what it could be. Are they all related?

  14. Trevor -
    If you have fluid on the passenger side of your vehicle; then you will most likely need to replace your Corvette Heater Core. When that Corvette Part is going bad/ leaking, the fluid usually ends up on the passenger side floor of the vehicle. This is a difficult install, you are going to have to remove a lot of the dash out of the car in order to get the heater core out. GM authorized somewhere around 6 hours for this by a trained mechanic with the proper tools.

  15. The mileage gauage on my 84 works for a while then it will either lock up at 7 mpg (or there abouts) or drop to 0. Shut the car off for awhile than it will work just fine…..then it may start acting up again. Never know what it is going to do. Sometimes, while driving, it will start working again.

  16. Hi Greg:
    The fans will automatically come on when the A/C is turned on. When the A/C is off the fan first fan will not come on until 225, the second fan is either 230 or 235. The fan temp switch is located in the cylinder head, not in the front of the Corvette engine. The sending unit in the front of the engine is for the computer and it is not a switch. The switch will only operate one fan unless you wire it to both relays. Each fan has it’s own relay and they are located on the LH side of the radiator shroud next to the upper hose. Good Luck!

  17. Gary:
    The mpg gauge is part of the cluster and it gets its information from the ECM. If the LED are what is not working then the entire cluster has to be rebuilt.

  18. Mark:
    If you’re having trouble finding that switch, then it probably means that no company is making them new. But you do have a couple of options for getting one used. First, you can go to a swap meet or a junkyard and find one. Second, there is the Corvette Forum. It’s a free website where Corvette enthuisist ask and answer Corvette questions. There is also a forum where you can buy and sell old parts. Some people online may have suggestions on where to get what you need. Third option would be Vette Masters out of Virginia Beach. They specialize in used 84-96 Corvette Parts. Their number is 757-490-2570.

  19. Hi. I also have a 86 Vette. I checked everything you said becuase my fan won’t come on. When I pulled my fan Relay by the Battery it turned on when I touch the relay . Would something else tell the relay to close . or is it just a bad relay I need to change?


  20. I have a 1990 corvette convertible with the 350 engine and my oil pressure gauge is not giving correct readings. I was told by someone I can view the oil pressure, temp and voltage on the digital portion of my dash. Can anyone tell me how to change the dash to view the oil pressure?

  21. Hi. I have a 1987 Vette and my mechanic says I need a AC Control Head – not the Face Plate. He cannot locate one, preferrably new, and my research has not turned up anything. The sliding control makes the AC and/or heater work only in the full cold or full hot positions. Any help would be appreciated.


  22. Bill:
    This AC Control Head is no longer available. Only the faceplate is still available.
    But you should be able to find it as a used/reconditioned part. We recommend you call
    Vette Masters in Va. Beach, Va at 757-490-2570. Good Luck!

  23. J -
    Why do you think your current readings are not correct? The buttons on the side of dash have different gauges that they control. Just depress the buttons until you see either the oil pressure or the oil temp. The oil pressure also has a analog gauge. Hope this helps.

  24. The radiator fan on my 1987 Corvette would not work causing it to run hot. It would run if you added power to it, but not come on on its own.The first thing I did was unplug the fan relay that is right by the battery and clean the contacts and hooked it back up. The fan came on and works like it is supposed to. The relay had alot of dirt and road grime inside the contact areas. The car is doing fine now.

  25. I have the same 1990 six speed L-98 and have constantly had problems when it’s hot outside. In my case, I’m sure it’s a case of vapor lock as the heat is trapped under the hood. I’ve gone in another direction and boosted the fuel pressure, which seems to have helped. Just a thought.

  26. I have a 1980 Corvette. The tumbler is worn out, key eng. switch on column to start the car. Now – how do you get it out of column? Chev dealer said my vin # showed it to be a 1980 el camino & checked on post & door ! Title vin. & all checked out ok, can you tell me what’s going on?

  27. Hi – what do you do when your fan motor is making noises when running and it has some slight play in it when turned off?

  28. Gene:
    You have to remove the steering wheel and hub, then the lock plate and the turn signal switch will have to be moved out of the way. There is a slot in the upper right hand side of the column. With the key turned into the ACC position you push a screwdriver through the slot and it depressed a key in the tumbler and viola, its out. As for your VIN question:
    1980 Corvette vin #’s started as
    1Z878AS400001 THROUGH 1Z878AS440614
    note: 5th didget will vary, depending on horsepower rating of car.
    Hope this helps!

  29. Thanks, I was having the same problem. Fan not coming on. Living in Florida, a car will over heat in a heart beat. Pulled the relay, jumped and fan came, Thanks!! Saved me hours of time!

  30. I have a 91 Corvette. At what temperature do the fans turn on? I’ve noticed they don’t turn on when I think they should. How do I make them turn on sooner?

  31. Walter:
    In a stock situation, the fans turn on at 210-220 and off at 195 (approx). We offer C4 Corvette Cooling System Parts -themostats, fan switches and replacement proms – that will work together to turn the fans on and off at lower temperatures; since cooler temps help to produce a more efficient-running engine.

  32. Hey car is getting hot. I noticed fans are not coming on also I have some black smoke coming only from the passenger side exh pipe. Plz help.

  33. Hi I have a 87 corvette C4, my fan won’t turn on either. I’ve replaced the relay, and the fan motor, including replacing the wiring to the fan from the relay. What am I missing? Could it be the thermostat is sticking, keeping it from opening up? Possibly the coolant sensor…any help would be appreciated because I’ve about had it with this! It only has 58,000 original miles. Thank you.

  34. Christina:
    If we are talking about your main fan, then the issue is inside the ECU. You can check it by going to the relay and checking the small green wire. When the engine is cold, it should not have a ground signal. If it does, the problem is internal to the ECU and it will have to be rebuilt. The ECU is what turns the fan on and off via the relay. There should be four wires on the relay, two large red or orange, one carries batt voltage the other goes to the fan. The blue wire should be hot as soon as the ignition key is on and the green wire is the ground, this gets grounded inside the ECU when the ECU sees that the engine temp has met the requirement to turn the fan on. Hope this helps!

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