03 Outback wagon, 4 cylinder, 5 speed, 172k miles.

Car threw CEL a few weeks ago, 519 code. Preheat circuit Air/Fuel sensor. Was original Air/fuel unit so decided to replace with OEM Denso upstream unit. All good for a day or so then light comes back on. at this point Called Mechanic and he wanted to look at it. He checked out the obvious things, bad connections etc in engine bay then called Diagnostic service(Intellifix I think).

He ran through some diagnostics with them and was told ECU was bad, replaced it with OEM used unit. Good for a few starts then CEL is back on. Checks out old O2 sensor and new unit for resistance, both units are between 1.8 and 2.3 ohms. Seems low. Calls local Subaru master tech and was told within specs, even gets a third unit to check, same readings. Mech suspects bad power to unit, maybe bad wire or relay. runs jumper to unswitched source. Car good for a few starts then CEL. Checks voltage to sensor from ECU- runs within specs then spikes- tripping CEL.

At this point I have spent time and money diagnosing with no resolution in sight, Mech gave up even after having car for a week and doing additional checks free of charge- just trying to fix it for his own edification.

Car runs well but won't pass emissions at this point I either fix it or send it to junkyard for parts. Was hoping for Subaru or experienced tech to give some insight.

Anyone have any ideas? I have about a month before car is out of time.Car is back in my possession, I can do some checks here, both electrical or mechanical.

Thanks in advance for any help you can give, Eric

DTC P0519 - IDLE AIR CONTROL CIRCUIT SYSTEM PERFORMANCE

 

A P0519 isn't for an O2 issue. It's for the idle air control issue.

 

So either you listed the wrong code or the mechanic is headed down the wrong path.

Neutral Switch on the Trans...... Subaru ONLY part...... not expensive at all.....

 

I have posted about it on USMB, but did a FULL WRITEUP quite a few years ago on the Forester Board:

http://www.subaruforester.org/vbulletin/f89/neutral-switch-78655/#post870591

I had the same issue on my 03 Forester, Check Engine light when coasting in neutral.  Saw the write up above, changed the switch and Check Engine Light gone!

super easy part to replace also.