A Crazy ECM.. any thoughts....

David52548 · 08-31-2008

I was out and about in my 2007 V6 Mustang yesterday and parked over near the beach. It was a very humid day, but I had the top down, and put it up and put the windows up while I went for a walk on the boardwalk. While on the boardwalk, it started to rain... and When I got back the humidity was so high I put on the AC... I like to use the upper and lower type setting which is one click counter clockwise from the off position. I hit the AC button and turned on the fan, then I looked and the AC light was out and would not come back on... I also noticed the fan was NOT blowing. I put the control to off and the fan came on and AC light lit again... Rotating the control to all of the counter clockwise positions did not shut off the AC, but when I got back to the off position, it would not shut off, and going one click counter clockwise, it shut off.. The going further to the other settings, it came back on. I shut off the engine and thought that might reset the ECM, but no.. same thing when I started the car up again. I was going to reload the stock tune in the morning as I have a Bamma Tune I am running. I figured I had a trip to the dealer to fix the problem. I go out today.. and everything is working normal. It is off at the 12 oclock position and would come on when I was one click counter clockwise...

I am at a loss as to what happened and why sitting overnight the ECM would suddenly self heal itself and be back to running the correct way. This leads me to wonder if this is why somedays the car is full of pep and other days it is sort of sluggish.. on the same tank of gas.

I was wondering if anyone has encountered this problem with their ECM or has an idea of what happened to cause the malfunction.

Dave

David52548 · 08-31-2008

Update....

I went out in the car for a little ride... and the AC seemed to be working properly.... then when the car reached its temperature the AC shut off in the first position counter clockwise... It came back on in the off position, but where it is blowing is beyond my ability to figure it out.. it seems like it is blowing no where with all the vents closed.

I am not sure not if it is a relay causing it or if it is the ECM going a little nuts when it gets hot... I felt it and it did feel very warm.. which it would be....

I did load the stock tune back and it had no affect upon my problem. Also checked for any DTC's.. there were none but did a clear anyway... the problem still persisted....

I am at a loss as to what is going on.. so it looks like a date at the Dealership.. at least it is under warranty.

GrayPony · 08-31-2008

Pass side carpet wet? Could be water getting into the smart junction box. I's a "known" issue that some have had.

**stlwagon** · 09-01-2008

Quote:

Originally Posted by GrayPony

Pass side carpet wet? Could be water getting into the smart junction box. I's a "known" issue that some have had.

That would be my thought too. Though it usually causes other 'electrical' issues too.

David52548 · 09-01-2008

Thanks for the thoughts... I will check if the passenger side carpets is damp or wet. I am also wondering if the problem may be a cold solder joint on a circuit board as the AC seems to function correctly till the car reaches the normal operating temperature.

This is a strange one... leave the car overnight to cool down and the AC will work fine up until the car warms up.

Dave

**stlwagon** · 09-01-2008

Be sure to lift the carpet and feel the padding. Often the carpet surface will be dry.

David52548 · 09-02-2008

Thanks for the tips, unfortunately my carpet is dry as a bone... I spoke with the Dealer and they will have to replace the AC module which has the fan, air flow and temperature switches mounted to it.
We will see what develops... I have an appointment for Saturday...

Thanks again for the hints on this .. it is now all the time in the broken mode... LOL