Radiator fan intermittently running and causing overheating

Tiny
NICKSCUD
  • MEMBER
  • 2003 TOYOTA COROLLA
  • 1.8L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 106,000 MILES
I have already replaced both radiator fan relays and this did not fix problem. When the A/C is turned on and dial set to coolest position this sometimes causes fan to come on, but not every time - result is engine runs very hot and/or in overheat position. Not sure what to do next. The fan runs, but not always. I thought relays were logical place to start, but they did not solve problem. What is next logical step? I want to fix problem but not keeping throwing parts at it. Since problem is intermittent it seems like it will be tricky to troubleshoot. Please help!
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Saturday, November 17th, 2018 AT 5:24 PM

2 Replies

Tiny
JONNYB1963
  • EXPERT
Hi Nick,

Thanks for visiting us. As to your problem. It be one or more of a few things. First thing as you stated that this was intermittent, I would start looking for loose or damaged wires, damaged connectors too.

Check the wiring between the fan fuse (30A) and the fan relay 1.
Then check the wiring of between the fan relays and the ECM.
The next thing I would check is the Engine Coolant Temperature Sensor.

Here is a schematic of the system layout.
See picture attached.

Jon
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Monday, November 19th, 2018 AT 1:44 PM
Tiny
KEN
  • ADMIN
Hello,

When the AC is on please check the fan motors for power. This will tell you if the motor is bad. Here is the wiring diagrams so you can see how it works and a guide to help you check for power:

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

There is an AC pressure switch that controls the fan motors as well (P2).

Check out the diagrams (below). Please let us know what you find. We are interested to see what it is.

Cheers, Ken
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Monday, November 19th, 2018 AT 1:47 PM

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