I pulled this code about two weeks ago. Ever since then, I've been searching the boards to see what the solution is. I know the actual code means high voltage on the front 02 sensor. However, in the threads I searched, some said it was the MAF that would cause this, others said it was the ECTS, and I think only one person actually said to replace the 02 sensor. So I'm lost as to what to try first. Basically the car would stall on start up when its cold out on first try only, it has stuttering at WOT above 3k or if you try and accelerate from 1k. Sounds like it's missing and the exhaust "pops". If you keep you hand at the muffler, you can feel bursts of air as it makes the popping sound and rpms drop with each pop. Trying to get this straightened out, and searching has only confused me. Should I just order the 02 sensor and start there? 0509 is the only code it's throwing. Thanks!

What year is your car?

O2 sensor codes usually can only be caused by the sensor itself, for the upstreams at least.

If your car is misfiring, chances are it's the coils; they seem prone to failure (especially in the '99s, if they've not been replaced).

It a model year of 98, with a production date of 07/97. So should I look into replacing coils as opposed to the sensor itself? Thanks pmorh!

Short of a wiring fault, or your ECU crapping out, they're going to be two seperate problems.

so start with the 02 sensor, and be prepared to move onto something else like coil(s)?

Personally I'd start with driveability problems first (misfiring), not O2 issues.

Check 6-pack.

is that a website or do you mean the 6 coils? I've already got a set of used ones I'm going to try and use at the end of the week.