Finally... it has arrived!
Non-permanent mechanical solution to the rear O2 CEL (P0420)
CEL free for 12,000 miles and counting! (as of 5/23/05)
First of all, let me thank our scooby friends for the idea:
Basically, this is a solution to the dreaded CATALYST EFFICIENCY BELOW THRESHOLD CEL (P0420, DTC 16804) that many of us get from upgrading the downpipe. The idea is to place a gap between the pipe and the sensor to reduce the amount of exhaust gases that the sensor will see/detect. This becoming a very popular mod over on the Impreza boards since it is NON-PERMANENT, and it does not require modification to the O2 sensor harness. Normally, I would throw a CEL about every 85 miles, so far this mod has been worthwhile.
1) Help! Part no. 42002 and/or 42009 by Motormite, these are known as sparkplug-arresters, which should be available at any generic auto supply store (e.g. Pepboys, Autozone, etc.). Should run about $5 per package.
- means to lift/secure vehicle
- 10 mm socket or wrench
- 7/8” wrench for O2 sensor (or 22 mm)
- drill and 1/2” drill bit (read below)
- Dremel tool and various bits
- zip ties & dykes
3) (most defly)
1) Jack up car and secure with jack stands.
2) Remove 2 plastic nuts and shield covering the O2 sensor/harness junction (10mm), this will make the R&R of the rear O2 much easier.
3) Remove the rear O2 sensor, which is the one downstream of the cat (7/8” or 22mm).
4) Modify the sparkplug-arrester(s). A 1/2” drill bit did the job for the Scooby sensor, but the vdub sensors are setup differently.
First I drilled out the arrester using the 1/2” drill bit, then I used various drill bits and the Dremel to shave the rest until the sensor would fit. If you have the means to measure the sensor and get the appropriate drill bit, that would be highly recommended.
5) Install arrester(s) into downpipe & replace O2 sensor (7/8” or 22mm).
From the pictures you can see that there are several combinations for the fix. The 42002 is a tapered-mount and the 42009 is a flat-mount with a crush washer. The 42002 (tapered) is notably longer in length than the 42009 (flat).
I elected to start off with the 42002 (tapered) only, which is the longer of the two, this worked out fine for 120 miles. Next, I placed a non-drilled 42009 (flat) in front of the 42002, so far no problems.
Another method for using two arresters in-line is only drill through both. Some Impreza owners have seen a SLOW RESPONDING O2 SENSOR CEL (P0139, DTC 16523) CEL. As you can see there may be some trial and error to find what’s right for your dub (specifically the cat or lack of in your downpipe).
6) Replace 2 plastic nuts and shield covering the O2 sensor/harness junction (10mm).
7) Secure harnesses with zip ties.
8) Clear DTC’s/Reset ECU.
That’s all folks!
Help parts again
42002 (drilled) & 42009
[******]As always YOU assume all responsibility for this mod![/size]
Modified by kdub790 at 3:52 PM 5-23-2005