RoadSpike

I helped my buddy install a full turbo back system including up pipe into his '04 wrx. We installed the cel fix provided with the down pipe but it kept giving us a p0139 sensor error. (O2 sensor slow response)

Installed parts:
Helix up pipe
Helix down pipe
Borla Hush Exaush
(Completely catless now)


Theory:
Since an O2 sensor pulses with a good frequency range of .8hz or 8 times every ten seonds and a minimum of .3hz i will assume that the cel fix lowers the pulse rate to a level thats too extreme.

The 04 wrx apparently measures the time delay in the o2 sensor with the voltage levels it provides. I assume the voltage levels are correct for the rear o2 sensor but the frequency it outputs is too slow making it appear like its a o2 sensor thats getting old.

Solution, Install new capacitor into circut using smaller capacitance to reduce time delay.

How this works:
The cel fix is simple, its nothing more than an eletronic time delay circut with a 1mega ohm resister and a 1uF capacitor. This translates into about 1 second time delay, a lil long on my scale.

Armed with this knowledge I made a custom circut using the same resistance but a smaller capacitor .22uF with the hopes that i can achieve the correct time delay on o2 sensor.

I'll keep your posted on the results of this lil test.

Any information regarding this problem and fixes that have already been found please respond to the thread

RoadSpike

good news!

I may actually have a working solution for the 04' WRX!

My buddy here says in a whole days worth of driving (2-3 hours on the road) no cel lights yet.

I will keep you posted if a cel does in fact come on

Any requests for wiring diagrams? i can whip one out.

RoadSpike

Here's a couple diagrams of both Cel fixes in case anyone wanted them

They will cost your about 2 bucks in radio shack parts.

barrelroll_9

Yup, this is an awesome fix for those of you with 04's that are replacing your downpipe! Jared helped me out with this one, and like he said, it took 1 or 2 bucks in parts as compared to the 20 or 25 you can spend online for a fix.

barrelroll_9

BTW, kick a$$ diagram. Thanks for the help!

DaWorstPlaya

iTrader: (1)

I do know the CEL fix for the O2 sensor for the 02-03 WRXs are different from the 04 .... thanks for clearing it up ....

RoadSpike

I should mention that there is a manical fix for the cel fix too. I heard (yes rumor) that a downpip from either greddy or someone else uses a method to hide the o2 sensor from the exhaust fumes.

The macanical fix is basically just a spark plug extender. You can find my mod and the other on scoobymods.com if you care to look around.

lin_tp2

iTrader: (7)

can some one find out if this solution works for 02-03 models as well.

AlanG

RoadSpike, did you originally install a mech. CEL fix and still get the P0139 code? Because I've installed the Helix mech. CEL fix on my HKS downpipe and started to get this code.... do I need to do your elect. fix aswell or what???

Thanks,

AlanG
2004 Wrx

MoneyMike

i believe when my brother got his up/dp catless combo, they installed the fix given with the pipes, and a day or 2 later the CEL came on. He got a dyno tune, since he installed an up/TBE and they just got rid of the CEL.