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How can i tell if the ecm/pcm is whats keeping the fans from coming on?

(2001 Chrysler Sebring)
in Clearwater, FL on August 01, 2014

Have a 2001 Chrysler Sebring 2.7 convertible. Fans don't cycle when they should.

Original problem was that the bleeder housing just exploded one day while driving. No

warning! The temp gauge didn't register hot or anything.

When I replaced the bleeder housing and bled the system everything seems fine until the temp

gets up to around 210-215 then the overflow tank starts to bubble and bucking sound. No

Fans. I can take the relay out Hi/lo and the fans go on and the car seems to cool. I can

unplug the sensor on the bleeder housing and get the fans to come on too.

There were compromises in the cooling system which I took care of.
I know that the system, according to previous research, has to hold 16 lbs. of pressure

before the fan relay gets the signal/pulse to come on and I'm sure with no compromises it's

reaching that.

Still no automatic fan activity.

I replaced the thermostat, toggle up at the top, the water pump seems fine, and the sensor

is new, came with new bleeder housing. I replaced rad cap.

I'm thinking that the ecu/pcm is not sending a signal to the fan relay. What would I check

to know for sure.

Oh I checked with an ohm meter the activity of the sensor with the engine running unplugged

and the numbers were going down on the sensor, don't know what that means exactly. I know a

little about the two wire and one wire sensors

So what can you tell me? I hope the answer is deserving of the charge.

Displaying 1 answers & 4 comments
Popular Answer
on August 01, 2014
Since this advice is FREE, I suggest having a scan test so live data can be viewed to determine what the PCM is seeing as engine temperature at the time of overheating! ... As well as a lot of other useful info and functional test that can be obtained from a 'real' scan tool!!!
on August 01, 2014
Hello Pushrod and thanks. Lets say I do have a nice scan tool that i use while the engine is running all the way up to 200 or so degrees at which point the fans haven't kicked on on their own, what of that information is gonna tell me why the fans haven't started on their own?

of G. T. Service Center on August 01, 2014
200 is not hot enough to turn the fans on, more normal operating temp.
on August 01, 2014
Scan tool can run a functional test to check fan circuits!.. See what the computer thinks the engine temp is as opposed to the temp gauge... IF the scanner can command the PCM to turn on fans... PCM is not your problem.! Let the engine run until it either boils the coolant or fans start!!!
on August 02, 2014
Thanks again. A more accurate description of what I actually have done before this discussion opened was to let the car run until the overflow tank started to boil at which point the fans had not started yet, top side guys I wrote exactly what I did, at which point it was Time to shut her down then guys! I've done this several different ways. By disconnecting the relays, hi/lo or via the temp sensor switch which trips the engine light, suppose to because of my interference, but forcing the fans on and the engine temp starts to cool off, right down until I shut it down at which point I reset my codes and I then started temp sensor ohm tests etc.

Assuming that the typical fan cooling circuit is where the problem is, there are only several basic components. The temp sensor, relay circuit, control module and the fans. I've ruled out all but the control module to be doing what they are supposed to be doing.

Whatever happened when that bleeder housing blew disabled those fans and still has them disabled. I'm going with the PCM! I might be a rookie here but I sure as heck ain't no rookie mechanic and I don't have to prove anything to anybody and am not trying to. This kind of stuff stumps the big dawgs and it ain't the first time, by a long shot that I have come up with an answer just through discussion like this one and my knowledge on what i'm doing.

I have other Chrysler horror stories that involved a primary firing circuit that was taken out when a crankshaft sensor failed on a Caravan once! The darn thing affected the PCM. The PCM disabled the primary firing circuit in that case. You couldn't guess the parts that people were changing out before they found the answer for themselves. My aim isn't to put my peps through all that! So I do the research and all the little things first like Finding out when the water jacket opens and closes and the fans turn on and off etc. The cap was bad. That kept the system from pressurizing at 16 lbs. i replaced it. The resevoir took a hit at the hose connection from the bleeder housing to the tank.

As the new cap made the system pressure go up that crack was revealed and eliminated in the tank. the PCM is supposed to send a signal to the relay at 16 lbs of pressure guys. The system wasn't reaching that, that's why I ruled the PCM out until the very last thing.


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