O2 Simulator

2/2/2015

Since turbocharging my IS300 this summer, I've been plagued with P0420 & P0430 codes -- Catalyst System below Efficiency. I tried simulating the output with my Innovate Wideband MTX-L, but after many months and configurations, I've given up. So I built a simulator based on a 555 Timer IC. I will install the new simulator tonight and report back w/ the results. Hopefully CEL free!

You can find the original schematics and instructions here.
http://mkiv.com/techarticles/oxygen_sensor_simulator/index.html

R1 100 K Ohm
R2 1 M Ohm
R3 100 K Ohm
R4 10 K Ohm
C1 4.7 uF Electrolytic
C2 22 uF Electrolytic
D1 1.7v@20mA LED
D2 1.7v@20mA LED

This is meant to fool the ECU into thinking the post-cat O2 sensors are working and the catalyst is within spec.
IMPORTANT NOTE: If you build this, make sure you do not leave PIN 4 on the 555 timer open (floating). This will cause operation to stop and/or reset with even the slightest EMF or input voltage variation. Instead, connect PIN 4 to Input Power. I connected to PIN 8 and it works flawlessly.

The only other improvement would be a smoothing capacitor on the output - just to make the signal more of a SINE wave as opposed to the square wave.

18 Comments

Jared

5/27/2015 10:34:39 am

Did the O2 simulator work on your IS300? Thanks

Jon @ Chippernut

5/28/2015 12:05:16 am

Yes - it worked fantastic. In this example I built two simulators on one board, but you only need one. You can drive both O2 signals by splitting the signal and inputting both to the ECU. Works great. Been CEL free since install.

6/1/2015 03:16:03 pm

Just built mine like you advised, it works great. One last question, did you weather proof it some how or did you just tuck it in the ecu box? Thanks!

6/2/2015 12:11:35 am

I ended up putting mine in the same box as the shift light Arduino -- which is a small project box located under my dash. You could weatherproof it and put it under the hood though, or I like your idea of tucking it in the ECU box (if it'll fit). Just keep it away from excess heat and water/mud. Glad you got it to work!!

Kelly

10/27/2015 12:28:19 pm

I'm not very savvy when it comes to stuff like this, but I'm very interested. How would I go about figuring out what I'm looking at, or how to properly execute this? My CEL is currently on, and I am all for a cheap fix. Thanks.

10/27/2015 12:52:22 pm

Hi Kelly,

I'll put together a better diagram and schematic with parts list -- I see the original website I had posted is no longer active. I'll remedy that. Check my.is - i'll post more about your post there too.

Joel1212

7/23/2016 07:11:42 pm

Did u ever post details on my.is? O2 sims are going for big bucks and it would be great to build one myself but like the previous poster I need more info n parts list

Farmer john

5/26/2016 11:38:34 am

What do you do with prong 5? And are the led lights needed?

5/26/2016 12:57:29 pm

I believe you just leave pin #5 disconnected. And yes, the LED's function as diodes and provide a small load to help it function correctly. Hope this helps
- jon

Zack

12/21/2016 10:06:25 am

Is this a plug and play type component or do i need to open up the ECU and do some cutting?
-thanks-

12/21/2016 01:41:36 pm

Hi Zack,
This is sorta plug-n-play. You will have to do some wiring depending on your plans. You will have to cut the O2 wire going from Ox sensor to the ECU (you can do this either at the plug or at the ECU harness). And splice in the signal from the O2 Simulator.

You likely have another circuit the ECU is looking for and that's the Ox sensor heater circuit. You can leave the O2 sensor plugged in to satisfy the ECU and either leave it in the exhaust stream, or tuck it away somewhere in the engine bay - although this isn't recommended as it gets VERY HOT. The best alternative is to splice a high-wattage resistor on the Ox heater wires coming from the ECU. Refer to your service manual for the correct ohms.

Something like this: https://www.amazon.com/Amico-Aluminum-Housed-Wirewound-Resistors/dp/B00899WR32/ref=sr_1_5?ie=UTF8&qid=1482349267&sr=8-5&keywords=high+wattage+resistor

Hope this helps
- jon

Dave

12/4/2017 08:57:28 pm

Where can I get the equations for this?

Gary Charlton

2/14/2018 11:23:39 am

Would the input positive be switched or constant?

2/15/2018 08:16:51 pm

It can be either - I have it wired up to constant in my car, it draws very little current, but it will drain the battery slowly over time. Switched input would probably be better. if you connect it to a power circuit that's powered when the key is in the "ON" position. Then it's only running when the vehicle is running.

4/8/2018 03:41:49 pm

Does the control voltage (pinout #5 need to be connected to anything?

4/19/2018 07:46:06 pm

No - you can leave this open. Hope this helps. Sorry for the delayed response.

Randell T gribben

4/26/2019 03:53:07 pm

Question, on the positive side, how do you reduce the voltage from 12 volts to 1.5 volts that I see here, 12 volts directly to the first led, would get it instantly
Perhaps I reading this wrong

4/27/2019 06:07:11 pm

The input is from the evil to sendor/ 555. And output from 555 to ecu?

O2 Simulator

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