My check engine light came on in June 2008. I immediately took it to the dealer, (I was on the road when it happened, 700 miles from home). Bowzer Hyundai in Pittsburgh was nice enough to read the codes, and told me they were PO136 & PO722. They suggested I get the flex pipe replaced in the exhaust. I did that. No luck. Next, I had the O2 sensor, (bank 1, sensor 2), replaced by my mechanic. (Or so he says it was replaced, I'm starting to have my doubts on that one). But the engine light is STILL on with the same 2 codes. I lost my job a year ago, haven't been able to find a new one, and this guessing game is getting expensive. As for the PO722 code, it's for the speed control sensor on the transmission. I've babied this car since I bought it brand new. The engine oil changed every 2,500 miles, transmission fluid changed every 12,000 miles. The transmission does not slip and has no strange failure symptoms. Now my mechanic wants to put it on the "BIG" computer, (as he calls it), probably charge me more money. First, am I getting a run-around from my mechanic? Second, wouldn't you think these sensors are just toast after 129,000 miles put on the car? (The car runs great, but the emission place told me that it won't pass emissions if the check engine light is on for ANYTHING). Stupid tree huggers. If anybody has any suggestions, please let me know.

 

You didn't say what car or engine you have.

Did you ever change the transmission fluid?

So did anybody clear the codes? If not, take the negative battery cable off for 15 minutes and see if the cel goes away.

Replace the transmission speed sensor. The output sensor, not the input sensor. That should take care of the P0722. You can have this from Autozone

The P0136 can be only three things. The DOWNSTREAM O2 sensor, an exhaust leak (flex pipe is common), or a bad connection. Get a universal O2 sensor from eBay and cut and splice the wires for $25 and replace the O2 sensor, as they do go bad over time.

 

Thanks. I've changed the tranny fluid every 12,000 miles since the car was new. I'm the original owner. Already had the O2 sensor replaced with a genuine Hyundai type. Also had the flex pipe replaced in the exhaust, so it must be an electrical connection issue. I just got my hands on a Hyundai trouble report for my car. The report says PO722 code is the fault of the pulse generator, so now I have 2 suspicious items for PO722. The output sensor AND the pulse generator. Which one do you think it may be? Thanks again !!!

 

Pulse generator is a generic term for these types of sensor. Your specific problem is the output speed sensor. Did anyone clear the codes, because the cel won't go away by itself. Pull off the neg battery cable and clear the code.

 

The shop that did the work said they cleared the codes, and the light was off for a week or two, then like magic, it came back on and has been on ever since. I'd disconnect the battery terminal, but I'm just so fed up with this problem, (it will be a year next month when it first came on), that I made an appointment with the Hyundai dealer. They're going to do the diagnostics on it for 50 bucks. They insist, that when they're done, I'll know EXACTLY what all the problems are and can proceed in fixing them. But, if I clear the codes now, it may come back to bite me on Thursday. Thanks for suggesting that though. If I wasn't so tired of this on-going problem, I'd give that a shot.