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Doug, ASE Certified Technician
Category: Mitsubishi
Satisfied Customers: 8612
Experience:  Mitsubishi employed and Factory trained ASE certified technician
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99 mitsubishi eclipse gs. a/c and radiator fans will not

Customer Question

99 mitsubishi eclipse gs. a/c and radiator fans will not come on
Submitted: 2 years ago.
Category: Mitsubishi
Expert:  Doug replied 2 years ago.
If neither the radiator or condenser fans will operate and this came to pass all at once, it is most probable there is a problem with the PCM (engine computer) on this model/engine.
The reason for this is that the condenser and radiator fans use completely separate relays, separate fuses, separate wiring etc. The only common components between the two are the PCM and the ground.
If you have already checked the fuses anyway (just in case multiple ones blew out), I would then pull the fans out and provide manual power/ground to them and verify they are capable of operating. It is possible that they just both happened to fail... unlikely as it may be.
If the fans operate manually, then I would hook them back up and use tester relays to manually apply stock power/ground and see if they work. If they do not, and you know your powers/fuses are good, then you would want to check the ground wiring. If they do work, then you would want to test the relays (as odd as it would be for three relays to all fail). If the relays are OK and you can manually power the fans with the stock wiring then you would know there is some sort of issue with the ground signal coming from the PCM.
For what it is worth, these PCMs are very common to fail, however this particular complaint is not too common... even though it is odd to see both stop working at once, I would still be inclined to expect a fuse or relay issue or just plain burned up motors.
Customer: replied 2 years ago.
ok. i have checked. my fans manually both of them are working. when it comes to the pcm i have changed it with another one that i have and still the same. i have found me a wiring schematics for a manual trans like mine. have check continuity on all cables coming and going from the pcm and everything seems to be good. the issue for sure is that the pcm is not sending the ground signal to the relays. does the vehicle speed sensor have to do anything with it.????
Customer: replied 2 years ago.
one more thing i know my car is running hotter than normal temperature since the fans are not running. why does the gauge keeps staying around normal temp. if i ground the cable coming out the sending unit it goes all the way up which it tells me that the gauge is fine.
Expert:  Doug replied 2 years ago.
If the issue for certain is that the PCM is not sending the ground signal to the relays, then your only considerations are the PCM itself, the wiring in between (unless you tested for ground right at the PCM connection), or that the vehicle simply doesn't require the fans when you are expecting them.
It is worth noting the fans can be considerably delayed in turning on... sometimes coming on after you exceed the normal operating temperature rather than right at normal temperature.
I would get your hands on a scan tool with actuator test capability and try to turn the fans on through the scan tool. If you can not, and there is no ground at the PCM when you have them activated, then the PCM simply is also bad. If you have ground at the PCM when activated via scan tool and the fans operate, then you just aren't hot enough to turn the fans on (either due to normal operation or the ECT sensor reading too low etc). If you have ground at the PCM when activated via scan tool but the fans do NOT operate, then check your relays are getting the ground signal or not, and if they are try a different relay etc... just work your way down the line.
Customer: replied 2 years ago.
how do i check pcm have ground. so does the vsc have to give signal to the pcm to turn the fans on. ?????i mean if its just the fact that the engine is not hot enough for it to come one. then why am i not getting ground on the a/c condenser fan when i turn the a/c on neither.
Expert:  Doug replied 2 years ago.
The VSS doesn't really enter in to it. If the vehicle is moving at high speed, the PCM then knows it doesn't need to turn the fans on since there is already sufficient air flow without the fans. Unless your speedometer is showing 60mph all the time or something like that, it is not going to be relevant.
I thought you had already tested ground at the PCM from your last response... if you have not, you can do so by checking pin 55 (for temperature related fan activation) and pin 69 (for AC related fan operation) for ground using a test meter set to resistance and measured between one of the pins and battery negative. If you have ground on the given wire under conditions where you would expect the fan to come on, then the PCM is working. If you are in conditions where the fan should be one (temperature reading 230+ for example) and you do not have ground at the PCM wire, then the PCM is bad.
Again using a scan tool with actuator tests for manual turning on/off of the fans would be preferred here to avoid running the engine hot.