My engine fan turns on when I turn the ignition on but not the engine. Why does it do that?

Asked by May 19, 2015 at 10:18 PM about the 1999 Toyota Corolla VE

Question type: Maintenance & Repair

I have a 1999 Toyota Corolla and when I turn the ignition switch on the motor fan turns on without the engine being on. The engine is cold and everything. I have researched and found out which relay switches are for each fan and replaced them, I have replaced the engine coolant sensor next to the thermostat, and I have replaced the computer. Granted all replacement parts were used. Relays were taken from a junk yard but had 6 total relays of the same numbers, and 2 sensors. I am playing off of the odds that there is no way that all relays and sensors are bad, and the computer I ordered was used as well. I do not believe its the computer but wanted to try. The car does not overheat or have any other malfunctions. My only concern is that the fan may eventually burn out from constantly running, and that its something that I want to know what is wrong with it. Do you have  any idea what it could be?

12 Answers

270

somebody could have wired you fan straight to the battery so when the car is turned on the fan could come on. they could have done this because maybe the other fan is broken (my corolla has two fans). also you do know that the plug that connects up to there thermostat housing if not connected will turn your fan on all the time this is a safety measure just incase the thermostat locks closed.

27 people found this helpful.
1,665

See attached photo. The Engine Main Relay (7) energizes when the ignition is in ON position. The Radiator Cooling Fan Relay (8) energizes when both the Engine Main Relay (7) is energized and the Engine Cooling Fan switch (10) is closed. The Radiator Cooling Fan Relay Contact (8) is normally closed, so when the Radiator Cooling Fan Relay (8) is energized, its contact is open. When the engine is cold, the Engine Cooling Fan switch (10) is closed. Therefore when the ignition is turned on and the engine is cold, both relays are energized, and the Cooling Fan Motor (9) does not receive any current as the contacts in Radiator Cooling Fan Relay (8) are held open. When the engine coolant comes up to temperature (90C), the Cooling Fan switch (10) opens and this breaks the coil current in the Radiator Cooling Fan Relay (8) which causes it to de-energize and "drop out". The contact in the Radiator Cooling Fan Relay (8) is normally closed, so it closes when the relay drops out. This provides a current path to the Cooling Fan Motor (9) and the cooling fan operates. Diagnosing: If you discover that the Cooling Fan Motor (9) is operating whenever the ignition is in the on position, then either the relay contact is permanently shorted (Closed), or the Cooling Fan switch (10) is stuck in the open position. In either case, the failure was a "safe" failure in that the fan operated in the event of the failure. In the cases where the Cooling Fan switch (10) becomes stuck in the closed position, this is an example of an "unsafe" failure as explained in this video: https://www.youtube.com/watch?v=-KVwivQaerE Fixing: Try the click test with the relay like in the video above. Then remove the relay and measure for voltage across the relay coil contacts. If there is no voltage, and you hear no click, the Cooling Fan switch (10) is stuck in the off position. If there IS voltage but you do not feel a strong click (but there is a weak click) then the relay contacts are welded together by arc-current. If so, sometimes, giving the relay a sharp rap on a flat surface, once on each side, will temporarily cure the problem by breaking the contacts free. If on the other hand you pull the Radiator Cooling Fan Relay (8) out when the engine is cold and the ignition key is in the on position and the cooling fan is still running, then there is a short between Engine Main Relay (7) power contact and the Cooling Fan Motor (9) The video above is for an older Corolla. This Video https://www.youtube.com/watch?v=w8BGMjDzL10 shows the layout of the 99 Corolla Relays. The green Relay (the one the guy is calling a "Condensator" ROFL) is the Radiator Cooling Fan Relay (8) and the Grey relay on the top right is the Engine Main Relay (7). Please post your experiences here after trying this diagnostic procedure as well as any additional findings, so others can learn.

83 people found this helpful.
1,665

The cooling Fan switch in 98-2000 Corolla is located in the thermostat housing behind, and below the alternator on the passenger side. You will need to remove the alternator to get at it. It has a single wire. A sender in the engine water jacket with TWO wires is the temperature sender NOT the cooling fan switch. Signed: Father with daughter attending school in another state...Yay!

17 people found this helpful.
1,665

If the cooling fan switch appears to be stuck in the off position, but then you measure a short circuit (0-10 ohms) between the cooling fan switch terminal and the engine block (indicating the cooling fan switch is closed), then there could be a fault (open) in the wiring harness. With the ignition OFF, measure the resistance between the cooling fan switch receptacle on the harness (you will have to unplug it to do so) and the cooling fan relay coil socket. One of the coil socket receptacle contacts should be connected directly to the cooling fan switch receptacle on the harness. Remove the cooling fan relay, then measure between contact 2 on Item 8 in the drawing and wire L or wire L/B on item 10. (should be zero-ten ohms). If not, the wiring harness has an open between those two points. Since you have already swapped relays and switches, this is likely the case. The most likely failure point is the end of the harness that connects to the cooling fan switch (item 10) at or above the cooling fan switch receptacle, since this receptacle is on the switch (item 10) which is on the motor and vibrates with the motor, which could fatigue the wire or the crimp connection at the receptacle. You could try cutting the receptacle off of another vehicle as far up the harness as possible (so you have the cooling fan switch receptacle on the end of say, 1.5 feet of wire), doing the same on your vehicle, and splicing in the "new one" (with BOTH solder and electrical tape, for sure) at the point where you cut off the old one. Let us know what happens!!!!

12 people found this helpful.
1,665

Here is a wiring diagram for a 98 from the library. I think it applies from '97 to ~2000 or 2001

27 people found this helpful.
1,665

The first drawing I posted disappeared. The first long post above refers to this drawing.

27 people found this helpful.
90

Mine because the expansion valve blocked(clogged) (not cool) so the pressure triggered by the AC pressure switch and make the fan always on...after change the drier and expansion switch all back to normal...(Toyota AE101 year 95) TQ

9 people found this helpful.
70

I have a 01 Toyota Corolla my engine fans do not turn on the car is running they work I hooked the wire to intestinal the battery must fans work and when I unplug the temperature sensor both fans turn on but my car will not start and I just replace the sensor any ideas

7 people found this helpful.
20

I HAVE THE SAME PROBLEM, ANY ANSWERS OR SUGGESTIONS

2 people found this helpful.
30

That is more than likely what they did it's where it's straight to the fuse box under the hood to a hot plug to a hot wire so as soon as you turn your ignition and it will start as soon as you turn it off it will turn off I have done this too many

3 people found this helpful.
20

I had the same problem after I had a new air conditioner compressor installed in my 2001 Corolla. Replaced the AC Pressure Switch and that resolved the issue.

2 people found this helpful.

i have toyota corolla 2002 le one week i drove with out runing raiderator fan one day i did pay attion fan not working and also coolant level was very low but i checked all hoses raiderator not was leak.i thought coolent sencor problem today i changed coolant temperator sencor but after this my engine not being on but when i try to start the engine right away start to run my fan.my question what going on why not start being on my engine and what is going on with my fan.plese can you let me know what is problem?

Your Answer:

Corolla

Looking for a Used Corolla in your area?

CarGurus has 62,125 nationwide Corolla listings starting at $1,500.

ZIP:

Toyota Corolla Experts

  • #1
    F_O_R
    Reputation
    2,900
  • #2
    G A Arne
    Reputation
    2,570
  • #3
    Jeff Polhemus
    Reputation
    2,480
View All

Find great deals from top-rated dealersTM

Search

Related Models For Sale

Used Toyota Camry
1,478 Great Deals out of 76,599 listings starting at $1,077
Used Honda Civic
1,043 Great Deals out of 62,754 listings starting at $1,000
Used Honda Accord
1,191 Great Deals out of 70,821 listings starting at $1,022
Used Toyota RAV4
1,497 Great Deals out of 64,372 listings starting at $1,994
Used Hyundai Elantra
1,175 Great Deals out of 52,285 listings starting at $992
Used Nissan Altima
1,663 Great Deals out of 69,781 listings starting at $1,650
Used Nissan Sentra
1,118 Great Deals out of 45,924 listings starting at $1,400
Used Toyota Tacoma
955 Great Deals out of 55,882 listings starting at $2,995
Used Honda CR-V
1,217 Great Deals out of 95,536 listings starting at $1,760
Used Toyota Yaris
80 Great Deals out of 5,906 listings starting at $1,995
Used Toyota Avalon
184 Great Deals out of 8,131 listings starting at $1,900
Used Toyota 4Runner
676 Great Deals out of 33,277 listings starting at $1,200

Used Cars for Sale

2020 Toyota Corolla For Sale
14 Great Deals out of 34,134 listings starting at $14,977
2019 Toyota Corolla For Sale
114 Great Deals out of 3,911 listings starting at $9,891
2018 Toyota Corolla For Sale
184 Great Deals out of 5,312 listings starting at $8,191
2017 Toyota Corolla For Sale
282 Great Deals out of 4,942 listings starting at $7,290
2016 Toyota Corolla For Sale
395 Great Deals out of 5,137 listings starting at $6,995

Content submitted by Users is not endorsed by CarGurus, does not express the opinions of CarGurus, and should not be considered reviewed, screened, or approved by CarGurus. Please refer to CarGurus Terms of Use. Content will be removed if CarGurus becomes aware that it violates our policies.