MKX03 Posted March 31, 2019 Report Share Posted March 31, 2019 My MKX over heated a while back, and I thought it was my fan control module that was bad. I ended up wiring up my fans to a switch to manually turn them on while I wait for parts to come in. I ended up finding a broken wire - the little wire that goes from the PCM to the fan control module. I fixed the broken piece and tested it. I turned on A/C on full and the fans started - I was pretty sure that meant it was fixed but proceeded to test further just in case. I immediately turned off the A/C and the cooling fans did not stop. Is this normal? It was hot outside, but the engine was cold, and had only been running for less then 1 minute. I let it run for about 2 mins to see if the fans would shut off, but they didn't until I shut the car off. (then they went off) Next test was to run the car with A/C off and see if the fans would come on once hot. At 213 degrees the fans came on for a split second then shut off (I was watching the temp with a code reader). So I waited until 230 degrees and the needle was going to h'ot' but the fans never came back on. So then I turned the A/C back on but the fans still didn't come on. I wiggled all the wires to check for any lose wires around - hoping the fan would come on. Today I tested again by turning on the A/C with a cold engine and the fans came on so that rules out many possibilities, but also leaves many others. Is it possible resetting the PCM could fix the problem? Maybe the fan control module is bad as I did have it connected with wires and relays to my switch when manually turning on my fans for 2 months. I will continue testing later or tomorrow 1 Quote Link to comment Share on other sites More sharing options...
WWWPerfA_ZN0W Posted April 1, 2019 Report Share Posted April 1, 2019 Checked the connectors at the module and at the fans for dirt/grit/rust? If present, clean it up, add a dab of dielectric grease, reconnect, and test. The passenger side cooling fan is the primary fan, the driver side fan only comes to life when climate control is involved OR the engine cooling demand is high. So if the engine is below 210F, and climate control is completely off, no fans will come one. Over approx 40 mph, as a rule, no cooling fan is needed for the engine to stay in-temp, there is enough airflow. Could be the module is bad. Very rarely, the refrigerant hi pressure switch is bad and can cause trouble also. But odds are new fan assembly is required. You could get it operating properly with the current equipment, but it is unlikely to last. Quote Link to comment Share on other sites More sharing options...
MKX03 Posted April 1, 2019 Author Report Share Posted April 1, 2019 (edited) So for me, BOTH my cooling fans are coming on when I turn on my AC. Which tells me something must be still wrong. And as I said, they won't turn off until I shut the car off. I have another (used) complete fan assembly / fan control module . And I just laid it on top of my engine and plugged my wires into that fan control module - I tested, and the same thing happened when I turned on the AC, both the fans on that assembly turned on and wouldn't turn off until I shut the key off. SO same thing. I didn't go as far as to run the engine to see if they will come on when the temp hits 210 degrees. As I am still convinced there is still a problem and I don't want to keep overheating the engine. I don't get what are the odds that I find a broken wire (from PCM to fan control module) and fix that, and would have bet a million bucks that would fix the problem, but now my fans are still not working correctly. Something else to mention, my AC doesn't seem to be cold anymore. Its somewhat cold on the passenger side, but warm on the drivers side. Not sure if this has any impact... It was very cold before, but its been 2 months now. It might just need a recharge. And I have the air filter box out (while working there) so the MAF sensor is disconnected which I believe has caused the car to stall a few times during testing, so I wonder if that could have have any impact? I just hope none of this caused my PCM to go bad Edited April 1, 2019 by MKX03 Quote Link to comment Share on other sites More sharing options...
WWWPerfA_ZN0W Posted April 2, 2019 Report Share Posted April 2, 2019 (edited) Yes, both fans turn on with climate control on. If the pass side fan is on already, the driver side fan will come on as well. The driver side fan is secondary, and works WITH the pass side fan, not solo. The fans should turn off if you turn HVAC off and engine is below fan activation threshold. If you have dual climate control, or if the coolant level is low, you can see temperature mismatch happening. Fans not working correctly will compound the problem below 40 mph or so due to insufficient airflow thru the condenser. The MAF sensor does not feed any HVAC data, only engine data. The AAT sensor behind the bumper cover however DOES feed HVAC data. Highly doubt anything like this would cause a PCM problem unless there was a surge/backfeed of some kind. Like applying external power to the connectors outside of system specifications. Edited April 2, 2019 by WWWPerfA_ZN0W Quote Link to comment Share on other sites More sharing options...
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