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Discussion Starter · #1 ·
Hi - I signed up here because I have a very unusual question about my (wife's) 2011 Santa Fe. Limited, AWD, V6 in case it matters.

The other day, we noticed a brake light was out. No big deal... found a spare 1157 I had and popped it in. Meanwhile I figured it would be nice to update to some LED 1157's like I've done on my other vehicles. Same brand I got before... popped them in on both rear brake lights (not the 3rd brake light, FYI) and they work fine. They'd come on when the headlights were on, and get bright when braking. Easy as that.

Well, the next day, the wife reported that she was having some severe issues. When turning (left or right), the car just would not accelerate. Pretty darn dangerous when making left turns with traffic! She was terrified to drive it so she borrowed mine. I spent the next few days and nights puzzling over this... all I did was change the 1157 brake/running lights to LED, and there's no way that would matter.

She also got gas the day before, so now I'm thinking "bad gas... did that station get some water in the underground tank?". I got some Royal Purple, dumped it in, topped off her half tank with 92 octane, non-ethanol just to give it the good stuff and see if it helped. It did not.

When I say it wouldn't accelerate when turning, I mean it might as well have been idling. I could stomp on the gas and nothing changed. But in a straight line or parked, it would rev like normal. Little V6 has some oomph! But turning? Forget about it. Curiously if I cranked the wheel to one stop or the other, it actually did better, but I think in that case it might increase the idle since the power steering is working harder? Anyway...

On my drive home from the station that sells the awesome "pure" gas, I was changing lanes when it also lost any acceleration at all. Well... that's weird.

Then the bulb in my brain went off... it's not just because I'm turning that I lose power - it's whenever the turn signals are active! Aha! And yes - confirmed. Left, right, hazards... if those turn signals are going, I simply can't accelerate. What the... ? Sure enough, if I turn myself into a lousy driver and don't signal when turning or changing lanes, everything is fine and dandy (other drivers might disagree since I'm no longer signaling, but hey, this is science!)

I get home, put the boring filament 1157's back in, and boom, everything is now back to normal.

So, the huge question is, what the heck? Has anyone ever run into anything like this before?

Bear in mind, the turn signal bulbs are entirely different than these brake lights. Yeah, they're next to each other in the rear lamp assembly.. are they sharing common wiring in some unusual way so that replacing one with LED would somehow so alter the car's delicate electronics, that the mere act of activating a turn signal would cause the throttle to throw up it's hands in disgust?

As strange as it is, my solution is "sorry little Santa Fe, you can't have any LED bulbs", but it's concerning that so minor a change as that would make the car want to kill us. :)
 

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Discussion Starter · #3 ·
Maybe the new bulbs are messing with the computer??
Yeah, it occurred to me that the problem could be the throttle position sensor having a weird issue with the new LED bulb. It's confusing to me why it only manifests when the turn signals are on though. In my mind, if there was going to be a problem at all like that, it should be whenever the running lights or brake lights are on, and then it's sensing that "aha, not enough power is being consumed by those lights, there must be an issue ... I know what I'll do, I'll refuse to accelerate because clearly I'm broken". Yeah, in my mind, the car talks to itself like that.

But really, could it be some type of ground fault? Perhaps the brake/turn circuit is shared with some other critical component, and even a small change like that is affecting the voltages somewhere in a more critical part of the engine operation besides merely "make lights go on and off"? My gut was telling me the TPS is involved in some way, but certainly the ECU could have some kind of bug.

I'm curious if anyone else with a similar year Santa Fe has done an LED swap of any bulbs and ran into unexplained performance problems. It might help me figure out if it's an ECU problem, a wiring problem, etc.

There's also the issue of why this happens even though no power should be going to those brake lights unless the running lights or brakes are active. The loss of acceleration happens even when those bulbs aren't in use at all. But I suppose the design of it may be sending some weak signal to them at all times, and it's seeing the higher resistance of the LED bulbs (compared to incandescent) as some sort of fault. And if it is sharing some common wiring with the turn signals, activating those bulbs is intermittently making the ECU think funny things.

Wait... is the 2011 Santa Fe using canbus? Is that part of my problem? (I wouldn't think so because burnt out bulbs give no dash indication, so if it is canbus, it's not doing anything)
 

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As an experiment, try driving it with the brake bulbs completely out.
Of course be careful where you do this, like drive to a big empty parking lot, then take the bulbs out.
I suspect the low LED brake bulb current is interfering with the brake light switch circuit; the engine computer thinks you are pressing the gas and brakes at the same time.
I also suspect resistors in parallel with the LED brake bulbs to bring the load current up to incandescent level will stop the malfunction.

Another experiment: before taking the brake bulbs out try accelerating while lightly riding the brakes with your left foot, with and without the turn signals.
 

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I will add my experience with converting brake bulbs to LED.
I bought these bulbs linked below, hoping that since they are some of the more powerful ones, their current almost as high as incandescent 1157/2357, they would wok well.
But no, I got bulb out warnings on the dash, but only when the headlights are on.
These LED bulbs draw 20 watts, compared to 2357 incandescent 28.5W.
When I turn on the headlights the battery voltage rises from 12.8V to 14.5V; the regulated LED current drops, then the error pops up.
I sat them on the shelf for 9 months before having another go to make them work.
A 27 ohm 25W resistor in parallel with each LED bulb adds enough current to keep the system happy.
 

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2012 Santa Fe Limited 2.4L FWD
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When I first got my 2012 Limited, there was an issue with the main ground that ran from the battery to the frame. The wire itself was okay, but the two actual bolts that connected to the frame barely had any connection. This caused me to have similar issues when any of my lights were on (headlights, brakes, turn signals) whether they were LED or not. Once I fixed that issue (a little sanding and greasing the connection) the issue seemed to completely go away.

It was after that fix that I started switching the rest of my bulbs to LED. I installed load resistors on all my turn signals (might be a little overkill) but everything is working as it should. Now every interior and exterior bulb is LED and I haven't been able to recreate the issue of any hesitation. I'm hoping your case may be as simple as mine was, but until you check all of your grounds, I'd hold off on any more LED lights for now.
 

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Discussion Starter · #7 ·
As an experiment, try driving it with the brake bulbs completely out.
Of course be careful where you do this, like drive to a big empty parking lot, then take the bulbs out.
I suspect the low LED brake bulb current is interfering with the brake light switch circuit; the engine computer thinks you are pressing the gas and brakes at the same time.
I also suspect resistors in parallel with the LED brake bulbs to bring the load current up to incandescent level will stop the malfunction.

Another experiment: before taking the brake bulbs out try accelerating while lightly riding the brakes with your left foot, with and without the turn signals.
I actually did try left-foot braking while also accelerating to see what would happen. Just light braking though, and it just made the AWD act funny as expected, but I had good throttle.

I searched around for generic cases of "turn signal" and "loss of acceleration" and surprisingly I found some hits where other people talk about the same or similar things happen. None pointed specifically back to having replaced other bulbs with LED, but the discussions did point to some interesting thoughts.

One common theme was that there actually is some interaction in the ECU between turn signals and braking, and that if it's detecting strange brake signals while you're indicating a turn, one thing it might do is just say "not today" and not let you accelerate.

I meant to try it out with just one LED and one regular bulb, but I was pressed for time and just went for swapping both back to see if that fixed it. It would be interesting to know if just one or the other would be okay - that would at least give a hint that putting in a load resistor would "fix" it.

My wife says that when one of the brake lights was out, it was still driving okay. It makes me wonder how it would be if both had burned out. The high center brake light on the hatch is still a regular bulb, for the record. Oh, and while I'm mentioning things, I had already replaced the backup lights with LED and those work great. No issues there. Interior lights are all LED too.
 

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Discussion Starter · #8 ·
...This caused me to have similar issues when any of my lights were on (headlights, brakes, turn signals) whether they were LED or not. Once I fixed that issue (a little sanding and greasing the connection) the issue seemed to completely go away...
It's an easy enough thing to check that main neg cable, so I'll definitely give it a go.

She used to have a 2004 Santa Fe that unfortunately got totaled when someone in a stolen car ran a red while being pursued by cops - didn't hit her car, but hit the car that hit her car and creamed the front end. She liked the Santa Fe so we figured an update to 2011 would be a nice little perk. Unfortunately she says it just doesn't handle as well. More rear sway on turns, we had some mechanical issues at first that made it stall out a few times (can't remember what it was, but the dealer seemed to think this was common).

In-laws have a newer 2014 I think and seem pretty pleased. I guess it's just hit or miss, or personal preference. :)
 

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It's an easy enough thing to check that main neg cable, so I'll definitely give it a go.
Would be good to check all the major ground ties.
Both ends of the battery cable, engine to frame, dash wiring harness etc.
it just doesn't handle as well.
Maybe it had a (10 year) life on rough streets. Maybe worn shocks.
Get a good independent shop to evaluate the suspension.
 

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Discussion Starter · #10 ·
Would be good to check all the major ground ties.
Both ends of the battery cable, engine to frame, dash wiring harness etc.

Maybe it had a (10 year) life on rough streets. Maybe worn shocks.
Get a good independent shop to evaluate the suspension.
Yeah, you're probably right about years of rough riding. We got the 2011 in 2019, so it had 8 years under its belt by the time we got it. I think it was at 90-92K miles at the time, so not terrible, but I could tell it wasn't driven by some grandma only on Sundays. No big body damage, but little things here and there.

I replaced the rear shocks which did help somewhat. The old ones were pretty shot.

I think it has more to do with the 2011 maybe having a higher center of gravity than her old 2004. I'm guessing at that. Honestly, I'm driving a Tundra, so a little sway when cornering is just par for the course for me... I chalked her experience up to driving technique and how a few changes in angles of approach when cornering can reduce that sway in the apex. LOL She was not impressed. :) It's been her daily driver now for a couple years and she's learned to live with it now. I think it's just one of those things when you're used to how one car operates, and everything else is rubbish. But then you get accustomed to the new normal. Same goes with new pairs of shoes, glasses, etc... always that awkward transition.

Regarding the brake light/turn signal/acceleration, I'll have to wait for the weekend to check those ground connections but I'll reply here with whatever I come across.
 

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It's an easy enough thing to check that main neg cable, so I'll definitely give it a go.

She used to have a 2004 Santa Fe that unfortunately got totaled when someone in a stolen car ran a red while being pursued by cops - didn't hit her car, but hit the car that hit her car and creamed the front end. She liked the Santa Fe so we figured an update to 2011 would be a nice little perk. Unfortunately she says it just doesn't handle as well. More rear sway on turns, we had some mechanical issues at first that made it stall out a few times (can't remember what it was, but the dealer seemed to think this was common).

In-laws have a newer 2014 I think and seem pretty pleased. I guess it's just hit or miss, or personal preference. :)
Cars are like watermelon, you never know if its coming out to be a red, sweet one, or white tasteless... It always makes me smile when someone sayin thing like: "The Hyundai (or Santa fe, or Subaru, or Ford..) are piece of crap, I had one and the transmission went after only 30,000 miles", well my friend, never heard the little saying "show me one, and i will show you 100,000" , the fact that your car transmission went early doesn't mean that will happen to all of those cars, its like if i would say "my granpa` smoked for all his life e didn't get cancer, therefore smoking doesn't cause cancer" some cars are just defective from the factory, some others are just good and never have an issue.
 

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Discussion Starter · #12 ·
... I'll have to wait for the weekend to check those ground connections but I'll reply here with whatever I come across.
I finally got around to checking the wiring, at least at the battery connection itself. Ground looks great - it's actually pretty clean in the engine compartment in general. No corrosion, the battery terminal connection is solid (which is good, since I put that battery in), and the connection to the chassis is rock solid.

I guess I'll chalk this up to a mystery for now and at some point I may probe the wiring at the taillights themselves, at least to see if the ground wire in the sockets is continuous/no resistance to chassis ground.

I'll have to replace the left-side rear lamp assembly thanks to a crappy seal that's letting water run right down the hatchback door and into the assembly. I slowed it down with some gasket sealant I had but even after drying out the insides the best I could, I think some is still getting in on the rainy days. So when I replace it, I may as well check it then. Who knows, maybe that water corroded some wiring in the bulb sockets making it do strange things.
 
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