Hyundai Transmission Mystery



I was in an accident a few weeks back and when I went to pick up my car ('97 Hyundai Elantra Station Wagon) at the body shop, the transmission was doing strange things. At first we thought it was a leak in the lines, but when that was cleared up and it was still acting up we looked on the inside…

The collision dented the front driver’s side, cracking the battery and spilling acid all over the insides. The guy says that there’s a sensor located right behind the drive line that looks like it’s been eaten away by the acid (and I agree)-- I have no idea what the sensor is, but I’m hoping you guys can help me out; here’s what the car does:

It generally shifts gears at 25-30mph, but though it accelerates normally to 25, the engine keeps going and the transmission doesn’t. Then, when you slow down or hit the brakes, it shifts hard and jerks the car. We’re thinking the sensor is what relays the RPMs to the transmission but since neither of us are transmission people, we’re not sure.

Any thoughts on what that sensor might be, if that’s the problem, or how much it ought to cost me to fix it?

There are no strange sounds, the engine runs as usual and the acceleration is smooth until that 25mph wall. The oil, power steering, coolant, and transmission fluids are all at their proper levels and there are no valves that are improperly open or closed or disconnected.


When you say “the engine keeps going and the transmission doesn’t”, do you mean that the engine RPM shoots up but the car stops accelerating, i.e. ‘neutraling’. The damaged sensor you describe could well be the transmission output speed sensor. It also could be the speedometer sensor (how is the speedometer reading). The signel from a transmission output speed sensor is used by the computer to determine the transmission shift points (governor in a noncomputerized transmission).

As an aside, is the check engine light ‘on’ or the O/D light ‘flashing’. If the O/D light is steady ‘on’, push the O/D button to the active position (light ordinarily ‘off’) and see if the light is blinking. If any of these lights is indicating, have the engine computer scanned for codes. The code can really steer you in the correct dirrection.

You are almost at the point where the services of a transmission specialist are needed. He would have the training, knowledge, and equipment to diagnosis this problem.

Hope that helps


Without seeing it, I couldnt tell you for sure but if its around the drive line, it could be a speed sensor. Hyundai’s usually have 2. An INPUT and an OUTPUT speed sensor. If there is a way for you to take a picture and post it, I could be more sure about it. Have you tried scanning the computer to see if there are any trouble codes??



Ah, yes, yes I do mean the RPMs shoot up but the car stops accelerating. I guarantee you the speedometer is spot on with 25mph-- I thought I was going to get run down. The check engine light’s been on for ages-- I got the O2 sensor replaced this summer because that’s supposedly what was wrong when we got the codes checked after the emissions test was done. The O/D light was showing on, but it was because they’d hit the button so that wasn’t flashing in any way.

I’m taking it to a transmission guy tomorrow, I was just hoping to have a feel for it-- being female, and in a fairly behind the times city, I tend to get the run around if I don’t have some grip on what I’m dealing with.


It is, in fact, right behind the drive line because the drive line had pressure on it right after the accident from the battery (which scared the heck out of me-- thought I’d done the transmission in for sure!). Unfortunately the car is a little ways away, but I’m taking it to the transmission guy tomorrow so being able to say it’s probably this or that will save me loads of trouble. I’ll bear repeating myself on this one-- Memphis is about 40 years behind the times and I’m female, so not knowing what I’m talking about can cost me more in time and money here.

thanks so much for your help!