Another Wild Electrical Issue
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Mountain Pass
Joined: Jul 2020
Posts: 109
Likes: 32
Another Wild Electrical Issue
2020 6.7L
Since new I have had this sporadic problem. The first week I had the vehicle the mechanics tightened some ground straps but the problem resurfaces every few months.
I enter my unlocked vehicle sitting in my garage. I depress the brake and press START. The truck doesn't start but ALL the external, dash and cluster lights flash with audible relay noises.
If you lock the door with the FOB and conduct a FOB start the truck starts. However, if you press the brake pedal (like you normally would for a start) the engine quits and the aforementioned lights flash.
If you lock the door with the FOB and conduct another FOB start the truck will again start and do the partial power up internally. If you press the START button without touching the brake pedal the rest of the modules power up. Now you can press the brake pedal and the truck acts as it should.
It has been to the dealer three times for this, they have never been able to replicate the problem. The batteries always test out ok... 30 years of technician experience from the heavy side poured of this truck for several days, nothing. They even hosed the truck down with a fire house... everything worked great.
I am leaning towards a defective BCM, module tests fine.
Since new I have had this sporadic problem. The first week I had the vehicle the mechanics tightened some ground straps but the problem resurfaces every few months.
I enter my unlocked vehicle sitting in my garage. I depress the brake and press START. The truck doesn't start but ALL the external, dash and cluster lights flash with audible relay noises.
If you lock the door with the FOB and conduct a FOB start the truck starts. However, if you press the brake pedal (like you normally would for a start) the engine quits and the aforementioned lights flash.
If you lock the door with the FOB and conduct another FOB start the truck will again start and do the partial power up internally. If you press the START button without touching the brake pedal the rest of the modules power up. Now you can press the brake pedal and the truck acts as it should.
It has been to the dealer three times for this, they have never been able to replicate the problem. The batteries always test out ok... 30 years of technician experience from the heavy side poured of this truck for several days, nothing. They even hosed the truck down with a fire house... everything worked great.
I am leaning towards a defective BCM, module tests fine.
Thread Starter
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Mountain Pass
Joined: Jul 2020
Posts: 109
Likes: 32
It happens on average once every few months. Doesn't seem to be linked to rain/moisture, more so when parked for extended periods. There have been times in between where the app notifies me that the truck has gone into deep sleep and yet the truck was only parked 3 to 4 days. I bought the truck in May of 2020 and it has happened about 6 times, the deep sleep about the same but not related to the flickering/relay cycling.
Thread Starter
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Mountain Pass
Joined: Jul 2020
Posts: 109
Likes: 32
I am not sure what procedure Ford uses to test the batteries. I will say that before I figured out that the truck could be started with the FOB I did take the negative leads off both batteries for 10 minutes and it fired right back up. Whatever error in a module or relay was gone at that point. That lends me to believe the batteries have always been good.
Mountain Pass
Joined: Jun 2020
Posts: 248
Likes: 40
From: Texas
since i've seen so many posts about the connectors at the rear of the truck above the spare tire getting filled with moisture and corrosion, maybe look there to see if you have anything funky going on.
Especially since you say it happens when you depress the brakes on a manual start, while a key fob start wouldn't require the brakes to be pressed.
Especially since you say it happens when you depress the brakes on a manual start, while a key fob start wouldn't require the brakes to be pressed.
Fleet Mechanic
Joined: Mar 2021
Posts: 1,455
Likes: 607
I am not sure what procedure Ford uses to test the batteries. I will say that before I figured out that the truck could be started with the FOB I did take the negative leads off both batteries for 10 minutes and it fired right back up. Whatever error in a module or relay was gone at that point. That lends me to believe the batteries have always been good.
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Mountain Pass
Joined: Aug 2021
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You can test both batteries individually without disconnecting them. Measure voltage (vdc) between the two poles (positive and negative) without the truck running.
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Thread Starter
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Mountain Pass
Joined: Jul 2020
Posts: 109
Likes: 32
Found myself with some downtime and took a look at all the connectors back by the spare tire, there are a bunch, maybe 7 or 8 in total. I inspected the internal pins and everything looked fantastic, so the connectors in the back are not the issue.
Had some other oddities, during a few daily errands the truck could not find or it took several minutes to find the XM receiver. At one point while using Carplay and making a call the entertainment system conducted a reboot, all is well now.
Looking into some AGM batteries. Any brand favorites?
Had some other oddities, during a few daily errands the truck could not find or it took several minutes to find the XM receiver. At one point while using Carplay and making a call the entertainment system conducted a reboot, all is well now.
Looking into some AGM batteries. Any brand favorites?
Fleet Mechanic
Joined: Mar 2021
Posts: 1,455
Likes: 607
Found myself with some downtime and took a look at all the connectors back by the spare tire, there are a bunch, maybe 7 or 8 in total. I inspected the internal pins and everything looked fantastic, so the connectors in the back are not the issue.
Had some other oddities, during a few daily errands the truck could not find or it took several minutes to find the XM receiver. At one point while using Carplay and making a call the entertainment system conducted a reboot, all is well now.
Looking into some AGM batteries. Any brand favorites?
Had some other oddities, during a few daily errands the truck could not find or it took several minutes to find the XM receiver. At one point while using Carplay and making a call the entertainment system conducted a reboot, all is well now.
Looking into some AGM batteries. Any brand favorites?
Thread Starter
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Mountain Pass
Joined: Jul 2020
Posts: 109
Likes: 32
Not immediately after. It seems to happen after a wash and a sit of at least 24 hours. In fact, several times it has gone into power save mode a day or two after being washed if the truck isn't driven immediately after.
Fleet Mechanic
Joined: Mar 2021
Posts: 1,455
Likes: 607
Are you washing the body only and not firing water underneath the truck? If it is related to washing then I would start looking for moisture/corrosion somewhere on everything on that circuit including looking at the bulbs themselves(are any LED?...). I would start at the 3rd brake light.