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04 Hyundai Santa Fe "limp mode"

I have a 2004 Hyundai Santa Fe with just under 97,000 miles on it. It’s a V6, 3.5L, AWD. I’m the second owner (parents were the first).

About two weeks ago I was driving down the highway during morning rush hour and the car seemed to loose power. (but not like it does when the alternator goes) and I had to pull over. The car wouldn’t go faster then 40MPH. I finally pulled back out into traffic and got to work.

Checked the coolant - bone dry. Filled up the coolant and it seemed to work. (also added power steering fluid as that was low as well) Friend checked and replaced the gasket on the upper radiator hose.

Few days later, same type of problems. Took it another friend. Replaced the gasket properly this time, found a tiny pin-prick hole in the upper radiator hose and fixed that.

Few days later, same problem with driving speeds. He did a read and it came up saying “Throttle Position Sensor” so after five junkyards, he found a replacement sensor. Test drove it after he fixed it and it was fine til after a few minutes. It wouldn’t go above 20mph…even with the gas pedal to the floor. Lights, heat, radio…everything else worked.

I also had a bit of trouble starting it when I pulled over yesterday (after him replacing the sensor). I revved the engine when I started it and it started but the check engine light came back on. And even with the gas pedal to the floor, it just wouln’t go.

He talked to some friends and did some research. They seem to think it’s going into “Limp Mode”. The car has trouble accelorating past 20 and does “okay” on side streets where the speed limit is lower…but has a hell of a time getting up to 25mph.

My next move is to take it to a local shop to see whats wrong with it. (one he trusts that won’t rip me off). All the research I’ve done hasn’t really given an answer. I’m not sure if it’s something that “could be anything” or if I really need to take it to the Dealership…

I think a local shop is going to be your best bet.

When it won’t go past 20 or 40 or whatever mph, what is the engine doing? What you actually describe can be read in at least 3 different ways. One is that you’re hitting the gas, but the engine itself has no power. It might run roughly. The rpms won’t get very high. It might sound like its bogging down or something. In this case you’re looking at a large number of different possibilities from old spark plugs, to low fuel pressure, to a clogged exhaust, to a blown head gasket.

Another read of it would be that you hit the gas and the engine revs up really high, but the car doesn’t keep speeding up because it is stuck in one gear and won’t shift. It will peg out at a relatively high rpm but won’t go beyond it. The engine will seem to be “screaming.” This would possibly be a limp mode thing, where the computer has seen a transmission problem so it won’t allow the transmission to shift. In this kind of case the rpms would go up and down steadily as you hit or release the gas pedal and every time you give the car gas you’d feel the power making it to the wheels.

Yet another read of it would be that you hit the gas, and the engine revs up really high for a bit, but than seems to “catch” and you motor along until it shifts at which point the engine revs up really high again…And each time the engine revs you don’t feel any power making it to the wheels, until maybe it “catches”. It also might not catch at all. This would be a slipping transmission.

Speaking of which, has anyone checked the transmission fluid?

When I press the gas pedal down, the engine will rev up to 3-4000 rpms but not go any faster.

Once I get going up to about 20mph it seems to be “better” but still won’t go any faster.

When I pull over and park, the engine revs on it’s own (not touching the pedal or anything) to almost 2000rpms.

Also, I noticed yesterday (when this all happened) that when I press on the brake, it makes a thud-thud-thud noise, but the brake does work and stops the car.

I do not know if my friend checked the Transmission fluid yet. I can’t assume he has. But I will ask him.

This sounds more like an engine problem than a transmission problem. By all means, check the transmission fluid for level, color and smell (it should be red, and should not smell burnt).

Is that check engine light still on? Head to your local parts place (AutoZone, O’reillys, etc), and ask them to read the computer. They’ll either give you a printout with the code and possible causes on it, or tell you a story about what could be wrong. It doesn’t really matter, just get the actual code (like P0***), and post it back here.

The engine shouldn’t jump to 2000 RPM’s when the car is just sitting, and it should rev easily with no load (e.g., sitting in park), going all the way to red line, which is well past 4000 RPM’s, more in the region of 7-8 or more.

I’m also concerned that the radiator was “bone dry”. The engine may have suffered overheating, but with no coolant to move the needle on your dash, you wouldn’t even know. Has it ever overheated that you know of? If it has, you may have a more serious engine problem to look into.

Post the code, answer those questions, and we’ll go from there.

Somebody with a good scanner, preferably one that reads live data needs to check this. The throttle position sensor needs to be monitored. Normally, a bad sensor won’t cause limp mode in the transmission.

transman

ok this is drive by wire if im right so yes something that simple can cause limp home mode because throttle vavle is electric instead of an actual cable

Did youi ever find the cause for this problem? I have a 2005 Sante FE that just started doing “exactly” everything that you are describing right down to the “thud, thud thud” when applying the brake pedal.

cigroller did not start this thread and it is 6 years old. Please start your own thread with clear decryptions of your problems and the replies will apply to you only.