1999 Subaru Check engine light & cobblestones

Hi, I have a 1999 Subaru Legacy sedan with 136,000 miles. The check engine light has been on and off since August. I have gone to 3 different mechanics & the dealer to try and solve the problem. The first one said it was the Oxygen sensors, the second said it needed a tune-up, the dealer said it needed new catalytic converters and the fourth said it needed tigher spark plugs. I’ve replaced the oxygen senors, the catalytic converters and gotten a tune-up. The light is still on & sometimes my car has troubles going up hills- it just doesn’t have a lot of power. Any suggestions? Is there anything else I should look into? Thank you!

I forgot to mention the cobble stone connection. I live on a very steep cobble stone street. Could driving up and down my steep cobble stone street be causing the light to come on?

yes,it can. tell that to your tech. its to much too explain,but has to do with misfire monitors

hope that helps

Drop by a local AutoZone, Checkers, Advance Auto, or whomever and have them pull the codes. Do not expect or ask for an interpretation of these codes. That is not their job.
Post any results back here for further discussion.

Lack of power could be a slipping clutch or a slipping transmission so it would help to know which one you have. Just as bad would be a differential trying to seize up.

There is a faint possibility this could be caused by a weak fuel pump or clogged filter (the latter can lead to the former).
Any bucking or jerking during all of this?
(If you have one of the auto parts houses pull the codes they will do this for you absolutely free and it only takes a couple of minutes)

The cobble stone street can “shake” things up. One sensor it may be shaking up is the knock sensor. When the knock sensor sends a signal to the engine computer, the engine computer retards ignition timing, which limits engine performance.
Get the trouble codes and post them here…such as P0xxx.

First of all sorry about hijacking this thread, but I think I have something similar and hope you’ll can help. I have a 1999 legacy GT wagon with ~133K miles on it. Just as the original poster the car really lacks power up hills and also the gas mileage has decreased over the last year. Yesterday the check engine light turned on, but other than it ran no different than before. This is when I found this thread. I just got back from Checker and they pulled the codes for me. The only code that came up was a PO400, something with the exhaust gas recirculation. The guy told me that it could have just been a loose gas cap, but am 95% sure the gas cap was on tight. He cleared the code and I drove about 6 miles home and it has stayed off.

Finally, my question, was it really as simple as the gas cap not on tightly or could this be a sign of a deeper issue? Thanks!!!


Since SubaruPgh isn’t talking, I’ll tell you that you’ll get more responses if you register and pose your question on a new post.
The trouble P0400 is a blanket code for the EGR (Exhaust Gas Recirculation) System. In no way is the EGR System connected to the EVAP System. So, the gas cap has nothing to do with EGR.