91 Corolla Cooling Fan Operation

[blb]

For some reason, when starting the engine cold first thing in the morning, sometimes the cooling fan will come on. It usually does go off after a few miles of driving. I've jiggled the wires, unplugged the sensors and swapped out both coolant temperature sensors with known good ones which had no effect on stopping the fan. The A/C is fully charged and operational. I guess the fan relay could be sticking intermittently. Has anyone else experienced this and if so, what did you do to fix it?

[Donald]

I am inclined to agree with you on the relay.
Try getting one from a salvage yard and swapping it out, see if that does it.

[datsa]

Originally Posted by blb

For some reason, when starting the engine cold first thing in the morning, sometimes the cooling fan will come on. It usually does go off after a few miles of driving. I've jiggled the wires, unplugged the sensors and swapped out both coolant temperature sensors with known good ones which had no effect on stopping the fan. The A/C is fully charged and operational. I guess the fan relay could be sticking intermittently. Has anyone else experienced this and if so, what did you do to fix it?

I had this problem, and I fixed it by cleaning the wiring harness connectors that attached the fan to the engine. I also cleaned the connectors that attach the distributor to the starter etc. It seems that when grease and engine oil get into the connectors, they cause a short that can do this sometimes.
Since my distributor has a leak around the axle bearing, a small amount of engine oil leaks out that then drips down the wiring and onto the end of the connector. When this happens, it can cause an intermittent short that remains until it is burned off.

I know this sounds crazy, but as long as the connector to the fan remained dirty, I had intermittent fan problems. When I cleaned the connector (disconnect both sides, with cotton q-tip clean inside, don't get any cotton fibers in it or remove them), then reconnect the connector. I notice that if I got the connector dirty, the fan would come on again.

[blb]

Thanks for the suggestions. I swapped out the "Fan 1" relay last night with a known good one and I will clean the fan connector contacts tonight and report back in a week or two with the results.

It's really a testament to the excellence of Toyota Engineering that the fan circuits are set up so that an "open" failure in a circuit results in the fan coming on when it shouldn't, rather that an "open" failure in a circuit resulting in the fan NOT coming on when it should which of course could result in engine overheating, and/or serious engine damage. The more I work on these cars and understand them, the more impressed I am with them.