O2 Sensor Simulator

[Trebuchet03 6]

Ripped from www.mkiv.com. If you know me, I am looking for better fuel economy... I have a few things up my sleeve, and I figured its time to show one of the things I've found (mostly because I just got the parts)... Original Link The Origins...

Oxygen Sensor Simulator

Casper Electronics is selling O2 simulator for OBD2 cars. It is about $40 and I ordered it right away to compare with my simulator. The simulator from Casper is very small, and nice looking with 4 wires coming out of it. I connected to battery and looked at the signal using voltmeter. The signal appeared to be quite similar to signal that 555 timer circuit produced, but appeared more random. It should work. I haven't tried on my car, but looking at the signal, it looks even closer to the real O2 data that I had collected earlier. If square wave signal was enough to fool OBD2 MKIV ECU, this one will fool it too.

http://www.casperselectronics.com/gp/O2SIM/index.htm {This link no longer works}

What is O2 sensor simulator?

The OBD-II cars (1996-1998) have the two O2 sensors to measure the amount of oxygen in the exhaust gas. First sensor is measuring it right after gases escape engine and this data is used to adjust fuel trim of the engine, as well as catch some faulty conditions. The second sensor is located after the catalic converter, and is used to detect the health of catalic converter. The ECU expects the signal from the sensor to be oscillating from below 0.4v to above 0.6v, but not above 1.2v, every few seconds when cruising.

If you install the aftermarket downpipe with no cat (which as we all know is purely for off-road applications) the ECU will detect this and indicate the error (MIL). The ECU is quite lazy at detection, and detects this condition approximately during second long trip. You can reset the ECU to clear the error code, but it's very inconvenient, as you don't really know if the error was because of oxygen sensor or some important thing is wrong and needs to be taken care of ASAP. It's also quite annoying.

How to build Your Own Oxygen Sensor Simulator!

The rest of the page shows how to build an oscillating signal generator with just the right frequency and voltage to fool the ECU. It is based on classical astable operating mode of 555 timer, so nothing revolutionary there. However we spent few days of fiddling and testing to get the right behavior.

The parts will cost about $15 - $20 from RadioShack. It's not that hard to build if you have some experience.

Components:

R1 100 K Ohm

R2 1 M Ohm

R3 100 K Ohm

R4 10 K Ohm

C1 4.7 uF

C2 22 uF

D1 1.7v@20mA LED

D2 1.7v@20mA LED

Additional notes:

If you use different flavors of 555 timer chip or LEDs with different parameters you will need to readjust the values of R4 and R2 to get the interval and output voltage right.

Don't attach it directly to the ECU right after assembly. Instead attach it to the battery and check the output. You should get approximately 0v/0.7v flipping about every 3.3 seconds when the car is not running, and 0v/0.9v when the car is running. The current should stay below 10mA.

One LED should be always on whenever the power is supplied. Another LED indicates when the output signal is high, so it should go on and off with the signal.

When tapping the ECU wires, triple check everything before hooking up the oscillator. The power source should read 0v when the key is removed, about 12.6v when they key is at ACC and about 14.3 when the alternator is running. The resistance between ground wire and the body shield of the ECU should be 0 ohms. And it would be best if you run the car and monitor the voltage of the original oxygen sensor wire before cutting it to make sure you have indeed got the right one.

The original sensor should still be dangling around, or plugged into the downpipe. The reason is that ECU also monitors the resistance of heater circuit inside the sensor.

Above testing and precautions will prevent you from frying the ECU and spending major $$$$. Anyway, I assume no responsibility if you still manage to do so.

END

So I got the parts from skycraft... I will be building this later tonight or tomorrow

If the square wave from the 555 is accepted without any codes, I will be modifying the circuit to allow the user to adjust fuel trim Again, my goal is not to go standalone... Oh I know someone else did a downstream O2 sensor simulator... I'm sorry, I lost the diagram if this is the same thing (or similar) do take some credit for knowing of this first (before my time here )

If the mods are happy, It would be nice to have this in the Tech Articles section... I'll do a follow up when its done on if it works on the upstream...

[plastic.racoon 1]

i made a post about this. It's called a "02 gome" so the dude at muffler man said, i have a number for a place in cali that have them and sell them.

Thanks for the info!

[Trebuchet03 6]

i made a post about this. It's called a "02 gome" so the dude at muffler man said, i have a number for a place in cali that have them and sell them.

Thanks for the info!

ahhh... so thats what that means I did not understand what that meant...

If you have a soldering iron, this is not too difficult to do.. the longest part is figuring out where the solder traces should go (which is what I do while I'm doing it ) B)

if/when you call, let us know how expensive it is B)

[crazykn 1]

I actually have all the parts in my scrap bin... but no use for this device. Build for fun?

[plastic.racoon 1]

I'd normally say build it and give to racoon. But i already have four points on my license and if i get caught without a cat, and get a ticket, i don't need anymore trouble with the Popo.

[Trebuchet03 6]

heh... this is not to get around not having a cat but would work for that...

I'm building it because I am going to be adjusting a/f ratios and burning vapor gas (which burns more completely - the ECU is not tuned for that)... I need a signal that give the A-OK code to the ECU I'll also be adjusting it so that the 555 stays on the lean side a little longer than the rich side B)

I just finished it... all I need is the 2 LEDs (which I fogot to buy)... so I'll spend 2.60 + tax at radio shack (for two 5mm red LEDs) when I could have spent .80 for two ultra bright blue LEDs

[plastic.racoon 1]

Or to get around the cat. :-p

[Trebuchet03 6]

Well, the device works B)

Using a 7volt power supply, it oscillates from 0v to .2volts.... I expect that number to go up when the right voltage is applied (we'll see)...

my only concern is the fact that it goes all the way to 0 volts... will the ECU freak out??? iono, these questions will be answered soon though I'm starting to research how this IC works so I can adjust the duty cycle to favor lean operation B)

--

EDIT:

OK, just did a "bench" test using my car's charging system as the "bench"

Results:

@12.40 volts (car off and sitting for about 4 days) - signal voltage 0.66vHigh - 0.01vLow

@ 14.56 volts (car running for about 1 minute) - signal voltage 0.85High - 0.02Low

Duty Cycle: About 7-8 seconds (counted in head) per cycle at 50:50 duty.

Maybe this weekend it will be installed (on a 2 way on-on switch)... I have to wait until parking services is not patrolling because I'll get a ticket for working on my car in the student lot I have a short video of it working if anyone is interested B)

Edited September 15, 2005 by Trebuchet03

[Trebuchet03 6]

Please note the EDIT in last post