Sign of electric gremlins coming?

Hey Guys, hope all is well. I miss you fuckers...
Anyway, been driving the mustang every weekend as usual.
Some funny codes happening and some symptoms that I can't ignore.

1st thing, I install some cool air horns about a year or so ago.
Simple ground to frame and line to battery, the horns stopped working a few weeks back.. just nothing.

2nd thing, yesterday... I shut the car off and the fan doesn't want to shut off EVER AT ALL.. I have to unplug it manually. WTF!?

3rd thing, P0300 random misfire detected & P0316 misfire detected on startup (first 1000 revolutions) so I am thinking spark plugs right? I feel like it's missing on idle randomly. so I will change those this weekend.

I think something is started to rot or corrode or something.. I feel like this is just the beginning.. any body have these symptoms?
something more sinister on the horizon for my baby!??
I know these types of things are chasing shit down in the harness and people end up wanted to drive their cars off a cliff...

Car has been running BEAUTIFULLY since forever... 123k miles on her.

Thanks in advance <3 143 xoxo

Did you install a relay for the horns? If so I'd check that first. If you have power at the horns then the horns are just bad.

As for the other symptoms, I'd check the SJB.

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Yes, I do have relays.. will be checking them this weekend.
SJB hmm maybe it's been getting moist?

SJB would be my first guess also.
Good to see you, Frankie.

Any chance it could be the battery?

Voltage pans out, battery is about 6 months old.
The car physically seems to run fine so far except for a slight miss at idle.
*le sad fdjizm*

Frankie - you check the alternator ?

bad alternator causes wacky electrical things in these cars

You may wish to begin working the issues one at a time. You've been given sound advice on the aftermarket horn gismo's so follow that up first and resolve it, if not simply remove it and return the car to stock in that aspect. Once this issue is overcome see below.

With regard to the cooling fan, as I recall there are two relays one for low and one for high speed. The PCM commands each as needed. A sticking fan relay on either of these two circuits would be the first thing to verify simply by pulling them one at a time when the fan is running (car off as you see the symptom) and see if the fan drops out. Hopefully it is just a welded relay contact pair and you can replace the relay. Otherwise it will be time to pull out a meter and begin trouble shooting the circuit causing the run condition in car off mode.

Best of luck. Don't get overwhelmed by trying to resolve all the problems at once. Just work them one at a time. Easily done even for an experienced troubleshooter.

Partout?

skwerl said:

SJB would be my first guess also.
Good to see you, Frankie.

Click to expand...

I don't see how the SJB would be involved. Horn maybe, but nothing else.

Fans are controlled by the PCM. As suggested above, the relay contacts welded or just sticking. OR, there is a problem with the relay trigger circuit staying grounded. The pcm opens/closes the ground to the relay coil to turn the fan on/off.

I would unplug C175B at the PCM when the fans stay running after you shut the car off. Fan stays on = bad relay. Fan shuts off = PCM isn't breaking the ground. I'd bet one of the relays is most likely the cause.

Misfire detection is done by the PCM. I would check/replace plugs first, and check compression while doing the plugs. Random misfire can be a bitch to fix.

Wes06 said:

Partout?

Click to expand...

Bwaaaahahahhaahaaa!!!

Should've used margarine.

stkjock said:

Frankie - you check the alternator ?

bad alternator causes wacky electrical things in these cars

Click to expand...

It's a brand spanking new (1 year) 2010 Mustang alternator. It's putting out 13.7-14.0 while the car is on.

redfirepearlgt said:

You may wish to begin working the issues one at a time. You've been given sound advice on the aftermarket horn gismo's so follow that up first and resolve it, if not simply remove it and return the car to stock in that aspect. Once this issue is overcome see below.

With regard to the cooling fan, as I recall there are two relays one for low and one for high speed. The PCM commands each as needed. A sticking fan relay on either of these two circuits would be the first thing to verify simply by pulling them one at a time when the fan is running (car off as you see the symptom) and see if the fan drops out. Hopefully it is just a welded relay contact pair and you can replace the relay. Otherwise it will be time to pull out a meter and begin trouble shooting the circuit causing the run condition in car off mode.

Best of luck. Don't get overwhelmed by trying to resolve all the problems at once. Just work them one at a time. Easily done even for an experienced troubleshooter.

Click to expand...

Yes, I will take it slow I guess I just got pissed and assumed this is the beginning of the fuckin end.

Wes06 said:

Partout?

Click to expand...

Bastard. -_-

Juice said:

I don't see how the SJB would be involved. Horn maybe, but nothing else.

Fans are controlled by the PCM. As suggested above, the relay contacts welded or just sticking. OR, there is a problem with the relay trigger circuit staying grounded. The pcm opens/closes the ground to the relay coil to turn the fan on/off.

I would unplug C175B at the PCM when the fans stay running after you shut the car off. Fan stays on = bad relay. Fan shuts off = PCM isn't breaking the ground. I'd bet one of the relays is most likely the cause.

Misfire detection is done by the PCM. I would check/replace plugs first, and check compression while doing the plugs. Random misfire can be a bitch to fix.

Click to expand...

Thanks man!! good information! I am going to check those fan relays.

bujeezus said:

Bwaaaahahahhaahaaa!!!

Click to expand...

Boaisy said:

Should've used margarine.

Click to expand...

Finally worked on the car today, one of the horns really did die and took a fuse with it.. replaced the fuse and 1 of the two horns work.
the fan was a BURNT relay, that shit was brown and boiling when I pulled it off. so the fan is fixed... Now I have this fuckin "stored" code...U1900 Can communication bus fualt and U2011 invalid/fault data received.

WTF? car runs fine thought and just got my new inspection sticker.

^^^ Nice job. As for the coms bus code.....yikes. Don't know much about can bus communications other than a basic definition.

Don't worry about those stored codes if you recently cleared old ones or startup unplugging things. Give it a drive cycle before rescanning.