Weird electrical issues?

[Danzofist]

Not sure where to post this on here so I can move it if needed but here goes:

I’m looking for a second opinion/advice/someone that’s seen this before.

Car info:
‘16 fiesta st

Cobb ap

Stratified 91 tune

No other mods

40k miles


A few days ago I was driving down the street and my car lost all power, but the engine was still running. Radio still worked. Heater still worked. Just no throttle response. The wrench light and the traction control light came on. Other lights flickered intermittently but not like a consistent blink or anything.

I coasted to the shoulder, turned it off and let it sit. Turned it back on and it fired right up. But still nothing happening when I push the gas pedal. Traction control light and wrench light stay on.

Now the ap keeps saying it’s looking for the ecu but it never connects. I turn the car on and off several more times with no luck. No response from the gas pedal.

Call my wife. She comes and gets our son, I wait for the tow truck and take it to the dealer where I’ve had all my work done and honestly have had a great experience so far.

They run diagnostics and tell me it threw 15 communication error codes. One of which is low voltage. Say they need to replace the battery to test further. Now this is where it gets muddy. On the ap, I have the voltage as one of the gauges and it’s been fine every day and was fine that day. Anyway, they replace the battery and do “extensive” testing (though they failed to elaborate on what exactly that meant) and tell me it’s 100% fine and the battery was the problem.

Now, I’m no master mechanic but I’ve done plenty of my own work on cars and this sounds in no way like a battery issue. There was no hesitation after several starts. All lights and gauges, the radio, the heater were working completely fine. And the car cut power but stayed on and idling. The warning lights flickering is concerning, but I didn’t think a bad battery would cause that. Or that a bad battery will cause the car to cut power while you’re driving. Bad alternator, sure. Definitely seen that before.

Has anyone experienced this? I feel like I’m getting a bullshit answer from the shop at the dealership, but if I’m wrong then please call me out and let me know because I’d like to be aware that this is a thing and a car can randomly cut power on you these days when the battery is starting to crap out.

Any help is appreciated.

 

[XR650R]

If all they did was replace the battery and it's fine now, it was just the battery.

Other people have had weird stuff happen with what seemed like a healthy battery that turned out not to be. These cars seem sensitive to that, with all the computer-controlled sensors and whatnot.

I imagine that replacing the battery fixed everything. "Extensive testing" seems a bit of a stretch. They hooked it up and cleared some codes, maybe? That's not a lot of work.

 

[Rocketst]

Yeah. I second the above. Computers these days require their sensors voltages to be with in such tight parameters if the battery cant keep that voltage up in theory it could create an issue. In practice I have a bmw e46 that threw a transmission light due to a positive wire burning through its insulation and grounding to the chassis. Car ran perfectly fine but it was a bit of a concern for a moment until I realized the cables had melted. As soon as I fixed the cable turned the car off and then back on it was completely fine.

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[TyphoonFiST]

Its all because of the Can-bus/ Controlled Area Network system...everything talks to everything unlike the old system.

 

[Scotman2]

Battery voltage is really critical on canbus vehicles. The various controllers and processors require very specific and consistent power feeds. If the alternator is trying to feed a dying Battery there could be issues ranging from strange malfunctions to damaged/fried bcm's and controllers. Added equipment like powerful amplifiers, driving lights or multiple, low demand electrical accessories on circuits that are maxed out, can create a witches brew of "strange shit". Power surges or sudden drop offs can do incredible damage. Our cars are basically the same as a computer, except with wheels and the ability to get exposed to all manner of climate conditions.

 

[TyphoonFiST]

This is why some Newer model vehicles come with AGM series batteries due to their ability to handle more powerful systems and drain themselves down and bring themselves backup many more times than a lead acid Battery.

 

[Danzofist]

Thanks for the input everyone. I guess I’m out of my depth when it comes to working on cars these days. They replaced the battery and I drove it home last night. Everything was fine. I’m off today but tomorrow I commute to work so we’ll see how that goes. Hopefully it really was just battery

 

[CarGuy]

Thanks for the input everyone. I guess I’m out of my depth when it comes to working on cars these days. They replaced the battery and I drove it home last night. Everything was fine. I’m off today but tomorrow I commute to work so we’ll see how that goes. Hopefully it really was just battery

I'm with you, it sounds odd to me too. Best to you. Let us know. Weird.

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[Scotman2]

This is why some Newer model vehicles come with AGM series batteries due to their ability to handle more powerful systems and drain themselves down and bring themselves backup many more times than a lead acid Battery.

I don't have any of the gel/ spiral cell type you are describing. But. I think their main advantages are energy density (they are fairly heavy) and stability under extreme conditions. They are basically a high tech deep cycle battery.

 

[TyphoonFiST]

I don't have any of the gel/ spiral cell type you are describing. But. I think their main advantages are energy density (they are fairly heavy) and stability under extreme conditions. They are basically a high tech deep cycle battery.

That is correct...

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[Danzofist]

Well, I’ve put 100 miles on it since the battery change and everything is running fine. Hopefully it really was just the battery even though having it lose power while you’re driving seems a bit extreme or like some kind of electrical oversight. But like I said, I’m no pro mechanic or anything so maybe that’s just the nature of cars now.

 

[Scotman2]

Modern cars are controlled by electrical signals it's not just windows and a radio anymore. The GO pedal is electrical. If you unplug it, it becomes non-functional.if you deprive it of power, it becomes non-functional. Connections and grounds in a modern car are just like a girlfriend, best enjoyed when clean and tight.

 

[CarGuy]

Modern cars are controlled by electrical signals it's not just windows and a radio anymore. The GO pedal is electrical. If you unplug it, it becomes non-functional.if you deprive it of power, it becomes non-functional. Connections and grounds in a modern car are just like a girlfriend, best enjoyed when clean and tight.

Nice analogy! Lol

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