26 replies to this topic

[speedster]

I have an O2 sim from http://www.o2sim.com installed, replacing the post CAT sensor. I've maintained the heater circuit and looking at the sensor via ODB-2 shows the correct mV is present. However the ECU is throwing a No Activity error - P0140 02 Sensor Circuit No Activity Detected (Bank 1 Sensor 2)

So, called into my local dealer today who plugged in their Tech 2 and he pointed out that the ECU appears to be expecting some activity, i.e. the voltage to fluctuate as the car shunts between richer and leaner settings. As the O2 sim is designed to produce only a static voltage he reckons the ECU appears to be wised up enough to figure that the reading is not from a working sensor and hence the No Activity error. I use the car daily and the EML appears when I've travelled around a 100 miles or so in a single session, that is intermittent small trips will not trigger the EML.

Wondering if anybody else with the sim has this issue or if anybody is using a more sophisticated sim?

[Pipo]

Only the pre-cat probe is producing a fluctuating voltage that changes with the quantity of oxygen left in the exhaust gasses. Thus letting the ECU know if the fuelmixure is too rich or too lean. But the post-cat probe always produces a stable voltage! This because a catalytic converter has the quality of stabilising the level of oxygen molecules in the exhaustgasses. And as a result the probe produces a stable voltage. If your EML light is still coming on and the ODB says it's the post-cat probe (and not the pre-cat probe!) there are 4 possible causes: 1) the probe heater is not working properly. But normally this gives a different fault-code, so the dealer can see that. 2) the voltage is fluctuating. This makes the ECU believe the CAT is not working properly. 3) your sim produces a stable voltage, but of the wrong level (too high or too low). Adjusting the voltage between 0.4 and 0.7 volt should cure this problem. On my NA the voltage had to be in a range between 400 and 500 millivolts DC 4) you did everything right, but somewhere you switched the positive and ground wires. If during the testing the EML-light comes on, you can easely reset the ECU-faultcodes by removing fuse nbr 8 (7,5A) during 15 minutes. (on a VX-NA) The faults are deleted and the EML light will be out. Of course, of you don't solve the problem, the EML will come on again. I hopes this helps you in some way.

Edited by Pipo, 09 May 2006 - 05:56 PM.

[Arno]

But the post-cat probe always produces a stable voltage! This because a catalytic converter has the quality of stabilising the level of oxygen molecules in the exhaustgasses. And as a result the probe produces a stable voltage.

Output from second sensor is not totally stable.

If you hook up an OBD scanner and plot the output of both sensors, you will see the output from the second probe increase and decrease as you accelerate or use steady-state throttle.

The output from the second sensor looks a lot like a capacitor charging and discharging, which is pretty much what happens as the engine management will only run close to stochiometric during steady-state closed-loop running.

The front one cycles in a 1 to 2 Hz speed between lean and rich, unless you accelerate (goes rich all the time) or release the throttle completely (goes lean).

This problem sound a lot like the O2 simulator is not working properly. These things usually use a 555 chip that generates a slowly oscillating signal, so the ECU sees slowly adusting values and figures all is OK.

It should most definitely not remain at a steady voltage.

Bye, Arno.

[Pipo]

I'm sorry Arno, but I don't agree. Before I constructed my own O²-sim, I did a lot of research concerning the principles of O²-sensors and catalytic converters. The signal will only decrease or raise if the engine is running lean or rich for a longer period of time, and the O² buffering capacity of the cat is not sufficient enough to cover that up. That's why the ECU accepts a certain variation in the output of the signal within a small range. After checking the signal of the second O² sensor with my scope, I constructed myself a device wich produces a DC-voltage adjustable between 100 and 900 mV. I designed it that way that the voltage remains unchanged and stable between a supply-voltage from 5 to 30 VDC. Then I adjusted it to 450mV. (as I said already, the ECU accepts different settings in a small range) Because I drove without cats at all, I used that device in my NA during about 10.000km, and never once the EML came on. The moment I disconnected it, the EML came on within 20km. I still have my sim in my possesion (planning to mount it again when I remove the maincat of my Turbo). If you're in the neighbourhood, you are more then welcome to test it on your car.

Edited by Pipo, 09 May 2006 - 07:51 PM.

[JohnyB]

Before I constructed my own O²-sim...

I remember reading those posts and also remember that you posted schemes and that you had problems.. etc

So you actually got the working version of it?
Can you post the scheme (the working one) ? I'll have it made.

Thanks.

[speedster]

Thanks guys for the replies Pipo I checked my installation and all is fine. The fact that I am getting a No Activity error does seem to indicate that the ECU is expecting some sort of activity on the sensor circuit Are you sure that your own DIY circuit is 100% stable? Intermittent changes of 25mV either way is enough to fool the ECU, so I been told. Arno, do you know of any sim that is running a 555 chip?

[Arno]

Before I constructed my own O²-sim, I did a lot of research concerning the principles of O²-sensors and catalytic converters. The signal will only decrease or raise if the engine is running lean or rich for a longer period of time, and the O² buffering capacity of the cat is not sufficient enough to cover that up.

Exactly!

This happens when you accelerate (engine goes rich, low/no O2 in gasses, open loop running, front sensor stops sending a oscillating signal and goes fully rich) or completely let go of the throttle (lean, high/full O2 in gasses, fuel cutoff, no fuel injected, front sensor goes fully lean).

After a little while you see the voltage on the second sensor either go up or start to drop as the cat either becomes depleted of oxygen or saturated and recover to the middle once the car is running in steady-state and closed-loop again. This does take a few seconds for the cat to react, but it does happen.

I'll try to post some snapshots of my OBD2 reader data plots with the O2 sensor data I did earlier that show this behaviour.

Bye, Arno.

[Arno]

Arno, do you know of any sim that is running a 555 chip?

A DIY option:

http://www.mkiv.com/...nsor_simulator/

Bye, Arno.

[cicastol]

I've done over 5000km with O2sim without problem of the EML come on,you need to make a little mods to get it working,try to search for the correct wiring diag (installation) posted by me on the forum,if i remember well you need to make a ground connection to get it working.

[speedster]

I've done over 5000km with O2sim without problem of the EML come on,you need to make a little mods to get it working,try to search for the correct wiring diag (installation) posted by me on the forum,if i remember well you need to make a ground connection to get it working.

Thanks cicastol. Found your details HERE

Difference is that you have grounded to the chassis. Will do the same and hopefully cure the problem!

[Pipo]

[quote name='JohnyB' date='May 10 2006, 10:13 '] [quote name='Pipo' date='May 9 2006, 20:07 ']
I remember reading those posts and also remember that you posted schemes and that you had problems.. etc
So you actually got the working version of it?
Can you post the scheme (the working one) ? I'll have it made.
Thanks. [/QUOTE]
There was nothing wrong with the scheme I posted. The problem was I didn't know at first that the ECU is also checking the build-in heater of the probe, so my device didn't similate that too. So in the beginning the EML came on even with my O²-sim connected. But reading the ODB-fault codes made my error clear.
So afterwards I left the heating wires of the probe connected (I was to lazy at the time to make another sim ), and the EML didn't came on anymore.

@ arno
I'm happy to read that someone on this forum does know something about the basic principles In Belgium we have a saying: "he heard the bell, but don't know were the clapper is". And a lot of advices are given based on that saying

At the time I checked the working of my sim, and the output didn't vary more then 8mv based on a varying supply voltage from 5 to 30 VDC. (which normally only can happen when your car's voltage regulator is broken)

PS: I hope to see you on the dummy-day

@ Speedster
Did you try your sim out on a turbo or the NA? Because it's possible the turbo ECU reacts somewhat different. Up to know I didn't try my sim out on my new Turbo, so I can't tell for shure. But personally I don't expect that.
Anyhow I'm planning to build a new sim wich includes the simulation of the heater too, so I can disconnect the second probe alltogether.

Concerning the grounding. My sim wasn't extra grounded. But it's using the + and - supply wires of the probe-heater. On my NA the probe was still in place. So there was an extra ground-connection there. Maybe that makes a difference, but I don't think so. Have to try it out once.

Edited by Pipo, 10 May 2006 - 03:17 PM.

[speedster]

@ Speedster
Did you try your sim out on a turbo or the NA?  Because it's possible the turbo ECU reacts somewhat different.  Up to know I didn't try my sim out on my new Turbo, so I can't tell for shure.  But personally I don't expect that.
Anyhow I'm planning to build a new sim wich includes the simulation of the heater too, so I can disconnect the second probe alltogether.

Concerning the grounding.  My sim wasn't extra grounded.  But it's using the + and - supply wires of the probe-heater. On my NA the probe was still in place.  So there was an extra ground-connection there.  Maybe that makes a difference, but I don't think so.  Have to try it out once.

Hi Pipo, i have the O2 Sim attached to an NA. My issuse does seem similar to the one that cicastol reported on so will give it a shot and report back

Here's what o2sim.com say's about the heater circuit

Can o2 sensor heater circuit be also simulated?

Yes. Generally o2 sensor heater circuit can be simulated with 40-60Omh 20watt resistor.

Edited by speedster, 10 May 2006 - 03:26 PM.

[2-20]

I had a O2sim on my car grounded to the chassis as suggested. I always got a Cel light after a while. The code detected was a P0141 which is related to the heater circuit. My +12v was taken from the heater circuit (normal way to wire it). I've been told that if there is a failure with the heater circuit the light comes on instantaneously. Is it true ? After different trials, and check of the connections, i never managed to have it working properly and i wondered what's going on. 2 weeks ago i removed it completly and rewired the sensor as stock. Now everything is OK so far, no light, but i'm not fully decated, i've a 100cell catalyst converter... These troubles have raised a few questions: Is there a problem with the software to read the codes giving a bad code ? Could the +12v pick up on the heater circuit influence the proper working of it ? Is there a way to set the output voltage of an O2sim ? pH

[speedster]

I had a O2sim on my car grounded to the chassis as suggested.
I always got a Cel light after a while.
The code detected was a P0141 which is related to the heater circuit.
My +12v was taken from the heater circuit (normal way to wire it).
I've been told that if there is a failure with the heater circuit the light comes on instantaneously. Is it true ?

After different trials, and check of the connections, i never managed to have it working properly and i wondered what's going on.

2 weeks ago i removed it completly and rewired the sensor as stock.
Now everything is OK so far, no light, but i'm not fully decated, i've a 100cell catalyst converter...

These troubles have raised a few questions:
Is there a problem with the software to read the codes giving a bad code ?
Could the +12v pick up on the heater circuit influence the proper working of it ?
Is there a way to set the output voltage of an O2sim ?

pH

The heater circuit maybe switched/controlled and in true oddball fashion the negative maybe the on the switching side.

O2sim.com have emailed me with two suggestions:

1. Don't use the heater circuit for the sim supply.
2. Ground to the chassis just incase the negative is switched.

[Pipo]

For supply of my own build sim I used the heater supply wires too. But my sim only consumes 30 mV max (like a small LED), so it doesn't influence the ECU. Theoretically the output voltage of the sim doesn't have to be adjustable once it is set right, but I constructed it that way to be sure I could always correct the voltage if in time the output changed due to aging of the electronic components. (at that time I didn't know how sensible the ECU was to input-variations) @ Speedster One info I still can't get my hands on is how our ECU checks if the heater is working. Does he measure the resistance of the heater, or does he checks the power consumption of it? At the moment I think it's the second option. Did you came across that info somewhere?

[speedster]

@ Speedster
One info I still can't get my hands on is how our ECU checks if the heater is working.  Does he measure the resistance of the heater, or does he checks the power consumption of it?  At the moment I think it's the second option.
Did you came across that info somewhere?

Not sure but we have either method 2 or 3 below. I reckon it is ECU controlled and based on my EML experience we have specific control circuits that monitor. Details below indicate thats its resistance that the ECU utilises.

There are three common methods of controlling the heating element in oxygen sensors. The first method provides a power source to the heater from the ignition switch or a relay anytime the ignition is turned to the run position. This method was used on many pre-OBD-II vehicles without heater diagnostics.


A second method supplies power to the heater through a PCM controlled relay. By controlling the heater power relay with the PCM, the circuit can be checked during key-off/engine-off periods.


The third method is limited to newer vehicles equipped with Fast Light Off (FLO) oxygen sensors. These sensors have a larger heater for quick sensor warm-up and are current flow limited through the PCM. Note that due to heater design and current draw differences, FLO oxygen sensors cannot be interchanged with other types. Inside the PCM is a switching transistor that pulse-width modulates the power supply, thus controlling current flow in the heater circuit. Using this type of PCM control, the FLO oxygen sensors can reach full operating temperature in as little as five seconds after startup.


One aspect of OBD-II vehicle diagnostics is the ability of the PCM to periodically test the HO2S for possible heater failure. As the name implies, the HO2S heater monitor (or test) is used to check the operation of the internal heater. Because the O2 sensor may be warmed by exhaust with the engine operating, a PCM actuated heater monitor typically runs after a predetermined ignition key-off/engine-off period. Specific enabling factors for this monitor may vary between manufacturers. When the heater monitor is running, the PCM measures the internal resistance of the sensor element as it heats up. Remember, the zirconia material changes conductivity with temperature. By energizing the HO2S heater element, and simultaneously monitoring the sensor signal circuit, the PCM should see the internal resistance of the sensor signal circuit go down as the temperature increases. This monitor fundamentally checks the integrity of the O2 heater element and its related circuits, as well as the O2 sensor signal circuit.


Full article HERE

Edited by speedster, 10 May 2006 - 09:35 PM.

[Pipo]

Thanks, now I know how to adapt my sim.

[speedster]

Thanks, now I know how to adapt my sim.

post your heater mods

[speedster]

OK... i am sorted. Using a seperate supply other than the sensor and grounding to the chassis have cure my problem

[2-20]

OK... i am sorted. Using a seperate supply other than the sensor and grounding to the chassis have cure my problem

What supply do you use ?

pH