AdamMikrut

My catalytic converter was recently stolen, and they also removed the air/fuel sensor by cutting the wires.

So I decided to replace it with a straight pipe and eliminate the sensor entirely. I’ve seen a lot of posts about this, but not a lot of precise info on how to do it, so I thought I’d try to provide some clarity.

First off, the downstream air/fuel sensor on an Rx300 (commonly referred to as an O2 sensor) has two circuits and is connected by 4 wires. Two wires control the heater circuit (to get the sensor up to operating temp quickly) and two wires control the air/fuel sensor circuit.

In order to bypass this sensor and remove the CEL and/or VSC lights on the dashboard, you need to deal with both circuits, since they both report back to the ECU.

Dealing with the heater circuit is simple. Use a 10ohm 25watt resistor between the two wires that control the heater circuit. In my case it was black and black/red. Even though the spec for the heater resistance in the repair manual says 0.8-1.4 ohms, a resistor of this size did not work for me.

Be careful where you fix the resistor, it can get quite hot. I strapped mine to the frame using a metal conduit strap.

For the air/fuel circuit, Magnum Tuning makes a gizmo that worked great for me.

https://www.magnumtuning.com/en/detail/ez-cel-fix-oxygen-sensor-simulator

It has 4 wires. Two need a fused, switched 12v power supply run to it (black and red) and two (black and gray) connect to the other two wires on your sensor connector - for me it was the white and brown. The brown being the ground.

Once you get these connected, reset the codes and you should be good to go.

salimshah

Just a cautionary note [I am not trying to sermonize/lecture] ... In many states, altering/faking/bypassing the emission control system is illegal and your vehicle may not be allowed to be on public streets. The limit is 25yrs ... getting close for first gen.

There is a science regarding metering of the fuel. The post combustion exhaust monitors the unburnt level of oxygen and the before combustion oxygen entering the engine and modulates the fuel supplied to burn.

As the fuel prices are rising, you may end up wasting more fuel and throwing away money by not having the system in place. I would suggest pursuing with insurance company. Your home owner/renter's policy may be an easier route as it is theft.

Salim

Lexmex

I am going to echo Salim on this. Despite all the exhaust modifications I ever had on my RX300, one thing I never drove without is that main catalytic converter despite replacing them twice with two Magnaflow cats. I still passed twice the Mexico City emissions standards which were California strict. This is not a heavy cost to replace at all in the United States.