ThatGuy

In this thread I'm going to try explain how to bypass the check engine code/light for the Subaru, 4-wire, heated rear o2 sensor.

Two things first off:

A HUGE thanks to Peaty for shipping me his MIL eliminator as made by ILP Performance, I'm assuming this is identical to the Pony Express ones, except to my knowledge, and I could be wrong here, those are for the newer 3-wire sensors. I don't know how widespread these specs I'm providing are, but they might work for any 4-wire (even non-subaru) application, or might ONLY work for a 98-01 USDM 2.5 RS. I really think though, it'll work for ANY 4-wire, as they are fairly universal.

SECOND. It is Federal offense (in America, probably everywhere else, too) to tamper with the Catalyst system on a registered, road-driven vehicle. This thread is to provide helpful information pertaining to the performance (I.E. engine management) to with a vehicle intended for OFF-ROAD applications....Track, Rally, etc...


Ok, now, according to my readings, ALL you will need for this is a 1 Killa-ohm resistor and a 1 Micro-ferad capacitor.

I'll provide a diagram, but for those who can't read it, try to outline the fairly simple circuit. The o2 sensor consists of 4 wires; 2 heaters (white), signal (black), and ground (grey). These colors are based off my OEM colors and Bosch. If those colors don't match, you'll have to research what the actual colors of yours are. The heater wires don't enter the equation, so don't worry about them. This leaves us with the ground wire and signal. cut the signal and ground so you have ample room to play with on either side (enough to slide a heat-shrink tube down, or enough so you can solder, or butt-splice....whatever you feel comfortable with). With the two lines cut, splice the resistor into the signal wire, and then the positive polarity of the capicator after it, on the connector side. you signal wire should now consist of: o2 Sensor, resistor, +capicator, connector - in that order.

As for the ground simply splice the negative side of the capicator into it. I guess you could just strip a small section of the ground wire, and not cut it, but again, whatever you find easiest/best.

I think this is easiest with the sensor off the vehicle obviously, but I suppose it's possible if you're small, don't mind lifting the car, or just like being cramped and working uncomfortably.

Diagram:

Attached Images

RearO2.jpg (52.3 KB, 570 views)