When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Engine, Exhaust, Transmission and DifferentialPost questions here that have to do with the engine, cooling system, air intake, exhaust, Transmission and Differential
Well, mostly. The FCM gets a pulsed 12v signal for the PTCM (ECM ) that tells it to supply X number of volts to the fan.
The shorted time between pulses, the faster the fan runs.
No pulses, no fan.
youre probably right about the fan. Dropped a new fan in. Worked perfect for a 10 min test ride. Got back and parked, fan sounds like a helicopter. At least it’s not heating up. Then shut it off, started the car back up, fan doesn’t turn on, and if and when it does. It sounds like a helicopter again.... then it slowed back down. So it appears to be working but not 100% when and how it’s supposed to. (The rad light is on and off intermittently throughout)
Ok, here is how it all works:
The ECM sends widely spaced pulses to the FCM, the FCM responds with a pulse each time it gets one form the ECM. If the pulse from the ECM is very short, it means: "Do not run the fan, but are you there?"
The FCM sends a quick pulse back that means: "I am here".
As the engine warms or the A/C is turned on, the ECM sends a wider pulse. The wider the pulse, the faster the ECM wants the fan to run.
Now, if communications break down between the FCM and ECM, this happens:
The ECM does not get that pulse back from the FCM, it lights the "General Coolant Alarm Light" which looks like a little radiator. Commonly referred to as the "Low Coolant Light".
The FCM is not getting pulses, so it has no idea how fast to run the fan, so it goes into emergency mode and runs the fan at 100% to protect the engine from overheating.
Which is what you are describing. The communications bus between the two is one bi-directional wire. You can measure the voltage on the wire but that tells you nothing. Grab an oscilloscope and see what you have - just know that NO WHERE in any documentation will you find the specifications of the width of the pulses. At one time, I tried to compare:
Cold engine - fan not turning
Cold engine with A/C on - fan running at minimal speed
Hot engine - fan running around 50% speed
Problem was, I could not find a set of triggering parameters that I could see the difference between the pulse from the ECM and the response from the FCM.
Back to your issue:
It almost sounds like the damn wire (or a connection at a connector at either end or a junction somewhere) has gone intermittent. I say this because it "comes and goes" which means that, essentially, both modules work at times. Of course, iit could be fractured solder on the circuit board(s) in one or other modules. The EMC is, I think, something you can take apart, but the FCM is hard to take apart. I have not seen this in any other car, but I have seen issues with wiring harnesses. Several SRT roadsters have had issues with the "duovalve" in the heater that I and Bob Davis, on separate occasions, traced to the harness.
Perhaps you have a connector at the ECM that is corroded/bad. If you change the FCM and it still does this, look at the ECM. As a last resort, you could run a new wire between the modules. Finding tools that will release the pins in the connectors, and finding the connector pins, may be a challenge.
Finally got the fan control module in. Thrilled to install it. Go to disconnect the factory module and it looks like there’s a retention band on it. Like little rubber bands on either side? How do I deal with these?
Scratch the last post. Got the module switched out. Run the car. Same problem. New fan, not responsive to ac being turned on. Radiator light on from the get go.
Granted the module I just installed is a used from eBay. But I’m lost. Tried and replaced it all. What else could be left?
Scratch the last post. Got the module switched out. Run the car. Same problem. New fan, not responsive to ac being turned on. Radiator light on from the get go.
Granted the module I just installed is a used from eBay. But I’m lost. Tried and replaced it all. What else could be left?
The heater/AC control on the dash causes problems, one of which is bad contacts between the two pieces that make up the module. See the Index of ...... in my sig and look at the AC section for details of the repair.
Also what about the sensor on the hose below the rad coolant overflow tank, is it plugged in or possibly failed? I may be grabbing at straws on that one.
Update. I installed a brand new fan control module 2 days ago, and voila... problem solved. Fan runs when ac on. Fan runs when car needs it to. No rad light. Everything is great.
2 days later.... drive car 20 miles. Car overheats. No rad light. Fan still running. But the car still overheating while driving. When idling the temp gauge begins to drop. So no rev = happy car.... rev = slowly climbs to H on gauge. It’s important to note that when I pull over or drop it into neutral and coast, the gauge shows it’s cooling... within 45 seconds it’s back to ideal temps. Shift into gear and drive, within minutes it heats up again. Thoughts?
Re: AC/Coolant/Radiator Combo HELP
