2015 Mustang Wiring Issues

[Chris Woodard]

Where to begin without making this too long...

MY son and I just bought a 2015 Mustang V6 that had slight front end damage. The car was advertised as running and the photos looked great. The detail that was missing was that the impact damaged the two wiring pigtails going to the PCM. The neighbor "mechanic" repaired the wiring (and i'll add he did a good job soldering and shrink wrapping) and told me he performed a diagnostic on the car and it needs a new computer. Before I go throwing money at the car, I thought I would start here first because there seem to be issues not related to the PCM.

The car will not start via the push button (however it will start and run if you jumper the starter relay). There are several warning that appear on the dash:
-Advance Trac Service
-Run Power Active
-Engine has shut off for fuel economy

The check engine light is on and flashing. It is throwing code P068A "ECM/PCM power relay de-energized too early"

I also find it interesting that most of the controls on the radio panel do not work as well. The 4 "-" buttons under the display, the "up" and "down" arrows below that as well as none of the A/C controls work.

I have checked continuity on all wires that took damage and they look good. I have checked all fuses and they look good as well. I have cleaned every ground and put dielectric grease on them.

Any suggestions as to where to start?
Thanks, Chris ... (and my son says thanks also =-) )

Sponsored

 

[Chris Woodard]

Anyone know a place that will reprogram a new PCM to my son's VIN? I can buy a brand new OEM Ford PCM for $488 at Tasca but they tell me it will still need to be programmed at the dealership.

 

[Billy1]

(1) Did you try disconnecting the battery(for at least 15 mins?), and then try re-starting it?
(2) Then, clear all the computer codes and see what happens(i.e. if they come back)
(-) Everything you state seems to be electrical related as the car will start and run with a jumper.
(-) It seems there is no electricity going to the dash
(3) You are going to have to figure a way to test all the dash components: starter button. A/C and radio(the radio would not be hooked up to the PCM)
(4) But before(3) Are you sure you found all the fuse boxes? i.e. you found the one with the radio. The radio fuse is fine and it still doesn't work? (I would still change all those related fuses for new ones)

 

[I Bleed Ford Blue]

I agree with Billy1, if your car will start then the pcm is fine, sounds like you have a harness problem somewhere under the dash, like a critter chewed some wires and fouled things up.

 

[Chris Woodard]

Unplugging the battery and resetting codes didn't change anything... code still returned. I did a visual of wiring under the dash and everything looks great with no evidence of animal (or human) tampering. I ordered a Ford wiring service manual to help with troubleshooting. Both the PCM and the PCM relay stay warm to the touch all the time even when the car is off. I am guessing this is the culprit of my battery drain as well. Another symptom that I find odd is that every time you power on the car it says that oil change is required... even after you just reset the oil life. As for fuses, I find it difficult to believe that Ford would have the up and down arrows for the console on a different fuse than the adjacent left and right arrows. 95% of all electronics work great but it is the 5% that has me stumped. When I hop in the car, the message on the cluster display reads "apply brake the start". I step on the brake and the brake lights physically come on but the display does not change on the cluster. I can depress the start button and I can hear a relay click in the BCM area but no power to the start relay. I suspect the BCM may be bad and I also suspect that the PCM has issues as well since it and the relay stay energized. I'll triple check the fuses again as well. I have purchased a new PCM but I am being told that even the PCM will need to be programmed at the dealership. Is it true that a factory new body control module will NOT need dealer programming? I miss the days of having 2 fox bodies in the garage and could interchange parts between my cars for troubleshooting. I can't pull much of anything off my GT350 that will help troubleshoot my sons car. =-(

 

[Billy1]

Did you run a vehicle check on the VIN? There might be more to the history of the car(accidents, flood etc.) than you know. As for the"Both the PCM and the PCM relay stay warm to the touch all the time even when the car is off", these are in a "Constant On" mode. You need to check the ground on these and trace the entire harness for each-yeah, definitely not easy.

With today's electronics, it is very likely that the BCM will also need programming. You will need to solve these problems before you install the new PCM and BCM because if you fry them, electrical items are not returnable/refundable. As for the old Fox days, remember when you were doing Terminator swaps you typically had to take the car to the dealer to reprogram the "PATS" system before the car would start.

As for right now, I would contact your local Ford dealer service manager(start with the one that you bought your GT350 from-letting the SM know you purchased from them in the past) to see if he can offer any advice/direction.

 

[Chris Woodard]

Well, I have ruled out wiring issues being an issue. After completely replacing both the front body harness and the engine harness as well as all fuses and relays the exact same issues are still there. I think my next move is to replace the BCM. I bought a factory service wiring diagram for his car and I can't believe how many interfaces the BCM has in the car. I am guessing it will be an item that the detail will need to program. This thing is turning into a bigger project than what I was anticipating... but I am secretly excited about that... because it is giving me some extra time with my 15yr old son... who seems to need less and less "dad" time these days.

 

[tokuzumi]

I like the South Main Auto YouTube channel. Eric O is very methodical with his approach, and details out his through process when he's diagnosing electrical issues. If a vehicle is having a lot of electrical issues, he will focus on one item (maybe in your case pressing the brake does not disable the "press brake to start" message), and traces the sensors and wiring from end to end.

While I'm not 100% certain, I believe the BCM would need to be programmed as well. The BCM needs to know what it can control, and what it doesn't need to worry about.

 

[Bestia]

Well, I have ruled out wiring issues being an issue. After completely replacing both the front body harness and the engine harness as well as all fuses and relays the exact same issues are still there. I think my next move is to replace the BCM. I bought a factory service wiring diagram for his car and I can't believe how many interfaces the BCM has in the car. I am guessing it will be an item that the detail will need to program. This thing is turning into a bigger project than what I was anticipating... but I am secretly excited about that... because it is giving me some extra time with my 15yr old son... who seems to need less and less "dad" time these days.

did you end up getting to the bottom of the issue?

Sponsored