CAN Bus Disaster over a battery.

F

Fordiesel69

Joined
Sep 10, 2005
Messages
2,787
Location
Erie, PA
My 2018 F150 only had its auto start / stop work for maybe a month last year in 2024. Then it never worked (thank gawd). The engine always cranked over super fast, even in cold weather.

2 weeks ago I heard an audible change in the starter sound, where it sounded like a normal car, not ultra fast like it usually does. Not long after I would get intermittent "drive modes not available", or "Traction Control Disabled", and a weird electrical behavior like slow and uneven turn signals.

Upon a code scan there were communication issues, and also
U0200 - Lost Comm With Door Ctrl Module B
U0199 - Lost Comm With Door Ctrl Module A

Charging was good, starting was slower but still good. I had battery tested and it scored a B-. It floats at 12.4vdc, then if you turn headlamps on it drops to 11.98dvc.

After changing the battery for a new AGM and resetting the BMC, it now has resolved all issues. It auto starts / stops every time now which is annoying.
 
Disaster? What disaster?

The truck gave you multiple warning signs your battery was on the way out. All the weird faults are the usual things that start happening, but the start stop not working is the first clue. You can access a screen that tells you why the truck is in the mode it is in. When it always says the vehicle is on for charging you have your first clue to monitor the battery health. Not abnormal for it to work that way now and then, but all the time is a clue.

If you have fordpass setup it would also be telling you that its disabling systems to protect the battery...
 
The high end NOCO chargers are compatible with these systems.

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There are so many issues on the F150 that if you have an issue many,many have had it before. It's a known issue that the start/ stop not working points to a bad battery. What's the big deal?
 
If the truck was so smart, why couldn't it just display a message on the dash that said "please charge the battery!"

I still don't get why so many components work poorly at low voltage. Yes I know they can have serious power draw, and have min voltage requirements--but the control bits ought to work down to low voltages and realize the problem, and not set incorrect codes.
 
They work poorly because when the voltage the ECM uses for a logic 1 or 0 is not in spec, it doesn’t know how to interpret it. That also goes for 12V field inputs. They also have thresholds for on or off. All of this can cause weird problems to start happening. We see the same type of problems in industrial electronics, especially microprocessor based equipment.
 
KGMtech said:
That sunroof issue would be horrible if you're hit with a rainstorm...in Florida !!
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I know! And I've never had a chance to try this out, but there's "theoretically" rain sensors in the sunroof to close it. I had skylights in my last home with that feature, and it worked great. Maybe, in this case, it uses the windshield cameras for the sensor. I know it does for the automatic wipers.
The manual is huge and translated from German, so it's pretty difficult to tell which car has which feature.
 
Rand said:
What was the disaster? I was figuring you had to do a proxy realignment or similar.
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What was the disaster?

The disaster was I thought it was the beginning of intermittent electrical issues which I have not found a mechanic skilled in electronics / can bus diags locally.

-Slow and uneven blinking turn signals
-Intemittent cycling / power on self test of the instrument cluster during crank (where the needles sweep and wiggle).
-Trac Control disabled / unavail message
-Drive modes unavailable.
-Comm issues / codes on the can bus.

My can bus crown vics, taurus, and old f-150's, 2014 ram, 2015 grand caravan never acted up when the batteries were getting low / worn out. So my mind did not correlate this. Rather these vehicles just cranked slow or would fail to start until they were boosted. No weird behavior.
 
ElectroMechanoMan said:
They work poorly because when the voltage the ECM uses for a logic 1 or 0 is not in spec, it doesn’t know how to interpret it. That also goes for 12V field inputs. They also have thresholds for on or off. All of this can cause weird problems to start happening. We see the same type of problems in industrial electronics, especially microprocessor based equipment.
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Most of these systems are not using 12V logic, the 12V line is regulated down. And CAN looks like it's 5V chips but signaling is around 3V (it goes up/down a small voltage swing, low voltage differential signaling).

Maybe the regulators drop out, not enough overhead or the buck convertors go out to lunch, but still, I'd think a robust regulator design could accommodate for this very common problem, unless if voltage is dropping really far, like 7V or less.

Maybe there's just that much noise going in when the battery drops low and cranking starts... still... "everyone" has had to deal with a bad battery or dead battery at some time or another. Thus "every" OEM ought to be designing their modules to deal with this, and not require a trip to the dealer for when the battery goes south so as to reset any codes. JMHO.
 
It just so happens that I was involved in a similar situation myself this past weekend. I got a call from my son at 10:40 Saturday night that his wife’s car was doing funny things…gauges and instruments look good, lights work, no crank. Shut off ignition and try again. Everything is dead. Try again, still everything dead. Let sit an hour, instruments ok, lights ok, no crank. Got a new battery and headed to Green Bay. Tried to start, everything is dead. Installed new battery, all back to normal, starts, runs, and drives. Back home at about 3:00AM. So yes, strange things happening, suspect 2 things. Look for a bad ground if battery is fairly new, replace the battery if it’s 5 years old or older.
 
supton said:
Most of these systems are not using 12V logic, the 12V line is regulated down. And CAN looks like it's 5V chips but signaling is around 3V (it goes up/down a small voltage swing, low voltage differential signaling).

Maybe the regulators drop out, not enough overhead or the buck convertors go out to lunch, but still, I'd think a robust regulator design could accommodate for this very common problem, unless if voltage is dropping really far, like 7V or less.

Maybe there's just that much noise going in when the battery drops low and cranking starts... still... "everyone" has had to deal with a bad battery or dead battery at some time or another. Thus "every" OEM ought to be designing their modules to deal with this, and not require a trip to the dealer for when the battery goes south so as to reset any codes. JMHO.
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My son and I talked about this quite a bit after our problems Saturday. I agree that the regulators may drop out when they see undervoltage. I don’t know exactly what type of circuitry they use, but CMOS runs 12v logic. Also, the output drivers also use 12v and we can’t tell how the outputs would interpret a low voltage. 5v is TTL logic and this is where a voltage regulator, depending on current demand, may act up if the regulator doesn’t have enough headroom.
 
ElectroMechanoMan said:
My son and I talked about this quite a bit after our problems Saturday. I agree that the regulators may drop out when they see undervoltage. I don’t know exactly what type of circuitry they use, but CMOS runs 12v logic. Also, the output drivers also use 12v and we can’t tell how the outputs would interpret a low voltage. 5v is TTL logic and this is where a voltage regulator, depending on current demand, may act up if the regulator doesn’t have enough headroom.
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Some CMOS runs on 12V, like the old CD4000 series. Many CMOS devices today run at 5V, 3.3V, and lower like 1.8V (and even lower!). Maybe some of the CAN bus chips today could run on 12V, but it looks like communication on the buss is around 3V. Link. I'd hazard most micros used in automotive applications are probably 5V powered (more because they have to have extensive testing to qualify them, and a bit of reluctance to change designs too often--nothing stopping 3.3V and perhaps I'm just wrong, maybe a number are 3.3V logic now).

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A micro could run at 3.3V or less and then use a communication chip to deal with the higher voltage signaling needs. That was very common with UART stuff. Some chips today will run on a low voltage, but on certain pins accept higher voltage so as to run a communication block that then communicates at higher voltages.
 
I’m relying on old knowledge 😬. I guess it’s time to bone up a bit! Thanks for the info. The one thing we can agree on is low voltage can and will reek havoc on microprocessor controlled systems.
 
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