Oxygen sensor simulator (for 96-98)
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
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.Electrical diagram:
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 Hookup:
Power source Ignition, or to the ECU
PIN #1Ground One of the ground points or ECU
PIN #80OUT ECU
PIN #47 (disconnect the O2 sensor wire)Catalog part numbers from RadioShack stores:
(NOT for their online
system)
276-309 5mm wide angle red led 1.7v, 20mA 276-1723 The 555 programmable timer 276-1995A The 8 pin socket for timer chip. It makes soldering safer and
replacement easier276-150A Generic PC board 64-3052A Pack of blue tap-in connectors 278-1225 Stranded wires (black, red and green) 270-1801 Small black plastic project box 3 x 2 x 1 272-1024 Capacitor, 4.7uF 272-1026 Capacitor, 22uF
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 resistance between ECU PIN
#47 and ground is about 1.3 to 1.6 M Ohm.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. If you want to COMPELTELY disconnect it, you will need to
measure the resistance of the heater circuit and install the right resistor
between ECU PIN
#72 and ECU PIN
#31 Anyway, there is no need to do it if you just leave O2 sensor alone and
only intercept the oxygen signal wire.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.Thanks to:
Mohd A, providing documentation
Nick P, running the
www.mkiv.com list,
Oolan Zimmer,
encouraging (and testing)
Steve V., RadioShack part numbers
Tovar
Millhollin, testing the prototypeAny
Feedback is welcome!
Awsome! one problem for me is the o2 senser is compeltely missing and i cant reed the heater sercet. were can i find this info on a 98 eclipse?
As I was known, Pre O2 changes from below 0.4 to above 0.6V for every few seconds, because rich and lean. Rear oxygen sensor is the rear side of catalytic converter to check the proper operation of catalyst. Oxygen density after the catalytic converter has to be within specific range around 0.5V when there is no acceleration or deceleration. So, output singal from below circuit changes from 0 to 0.7 V for every abour 3 seconds. Here is my question: Is this for Pre O2 or post O2. Thanks. Could you clear this for me. I confuses.
How can I add this circuit in four pin oxygen sensor
https://www.easycarelectrics.com/wp-content/uploads/2021/12/Oxygen-Sensors-Signal-Wires-Test.jpg?ezimgfmt=ng:webp/ngcb1
A 4 pin O2 sensor has it’s own separate ground (better than using the exhaust pipes as one) Just leave it be as with the heater circuit. Just follow what is described here just using the O2 sensors + (positive) sense wire just as you would a one wire or two wire , etc..
I couldn’t find a 1.7v 20 amp led here. What else can I use instead?
https://www.mouser.com/c/optoelectronics/led-lighting/led-emitters/?vf%20-%20forward%20voltage=1.7%20V
You can use zener diodes right before it gets to the signal wires, in order to protect the ECU from any excessive voltages.
Good morning! I have created the circuit as well I do have some questions.
Is pin 4 and pin 5 left open? Or did you tie p5 to p8 and p4 to cap to ground?
I installed in car but the code I get now is b1s2 o2(post cat) resistance too high. I cut the signal from O2 and soldered output from circuit to signal going to ecu.
Should I have left the wire connected and tapped in with the circuit output?
The circuit is getting power from ignition coil harness as it was the only one I could find that had keyed on power and not constant as to not drain battery.
Looking for some insight,
I have made the circuit as well I do have some questions.
4 Pin O2 sensor.
I installed in car but the code I get now is b1s2 o2(post cat) resistance too high(not resister circuit). I cut the signal(Black wire) from O2 and soldered output from circuit to signal going to ecu.
Should I have left the wire connected and tapped in with the circuit output?
The circuit is getting power from ignition coil harness as it was the only one I could find that had keyed on power and not constant as to not drain battery.