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About the O2 Sensor

 
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Old 08 Jun 2003, 10:52 pm
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Default About the O2 Sensor

I finally broke down and spent the bucks for a set of 2003 PT Cruiser Diagnostic manuals. Here is the description of the O2 Sensor's operation:

************

O2 Sensor (NGC)

The O2 system with the ignition on and engine off has a normalized O2 voltage of around 5 volts as displayed on the DRBIII or measured with a high impedance voltmeter. As the O2 sensor starts generating a signal the voltage will move towards 2.5 volts. The voltage will typically vary between 2.5 volts and 3.5 volts on a normal running engine. The goal voltage is also typically between 2.5 and 3.5 volts. This implies that the 0-volt through 1-volt range that you are used to is shifted up by a 2.5 volt offset. This 2.5 volt supply is being delivered through the sensor return line.

**********
Here are some notes (from the manual and elsewhere)
Notes:

NCG = Next Generation COntroller. This is the term for the new PCM that integrates the Transmission Controller internally. It also introduces some new diagnostic prpocedures and new DTC numbers.

DTC=Diagnostic Trouble Code

DRBIII - Scan Tool / Diagnostic instrument used for NGC PCM diagnostics, and provides communication with the PCM (2 way; input and output).

High Impedance Voltmeter = The Ohms per volt specification is an indication of a voltmeter's usefullness in measuring low current voltage sources. The higher Ohms per Volt reading, the less likely the meter's internal resistance will "load" the circuit under test, thereby giving false readings. This is a carry over from analog meter movements, and not as prominent a concern with most modern digital meters.

Sensor Return Line = Normally considered a signal ground; this is the reference level against which the voltage is measured. In theory, a blocking device, such as a diode, could be used in the return line to provide a "tap" for the 0 to 1 volt levels that most A/F gauges are looking for, while blocking the 2.5 volt offset from the measuring device (A/F meter). But, then again, the blocking device must not "load" the circuit when connected to a measuring device (ie A/F meter). There may be room for development here..

Here is a basic wiring description of the 02 sensor connector:

4 pin connector

1..... Ground
2..... O2 Heater Control
3..... O2 Return
4..... O2 signal

Pins 1 and 2 heater circuit.
Pins 3 and 4 O2 signal circuit

Diode 1N915 or 1N4148 (possibilities)

I don't know if this is a working theory. If you were to determine the average O2 sensor voltage, and then try the tap, the project could be considered a success if the average O2 voltage did not show a decrease over average readings once the tap and A/F gauge was in place.

This is probably low on the list of usable information. Installing a normal 0 to 1 volt sensor for the A/F gauge would be a lot easier in the long run, but being able to use one of those heated O2 sensors that are already there should give a more stable reading.[:I]
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Old 09 Jun 2003, 01:33 pm
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Dalite,
Knowlege is power. You have now become a PT-GT god, with service manuals at your right hand. I am truly envious.

Seriously, I appreciate the fact that you try to be spot on with every post!!
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Old 09 Jun 2003, 07:11 pm
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If you plan on installing a diode inline you will only get a .7v drop which i think will still not be enough. The best thing would be to change the resistors in the a/f gauge so they read on a higher voltage scale. Question of the day is:

What voltage = what A/F?
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Old 09 Jun 2003, 11:03 pm
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Kirby, thanks for the attaboy. I want to be able to provide info from the little I am learning, and correct past bad info I have posted before getting the facts straight. The O2 sensor has been open to a lot of speculation, and the Diagnostic manual seemed to have the most info on it.

Hector, the diode can be used in 2 ways; to block voltage when installed in one direction (the plan is to block the 2.5v on the sensor return line) to render the industry standard 0 to 1 volt signal that most A/F gauges are looking for. When installed in the other direction, you are correct. It provides .6 to .7 voltage drop, but it passes voltage. I think the technical definition is that by installing it inline this way, it raises the ground potential by that voltage (.6 to .7), yielding a net drop in the measured voltage of the circuit.

These aren't the greatest of explanations, and I still don't know it the diode being present to block the 2.5v on the sensor return line would add enough of a load to the circuit to throw off the O2 sensor data that the PCM is reading.

One thing for sure, after reading the part in the diagnostic manual about the O2 sensor, my earlier post about the O2 Sensor being pulse width modulated was way off. That is the treatment the injectors get to determine the amount of gas goes through them by changing their duty cycle; or varying the width of the pules of electricity that makes them squirt.

On the resistors in the A/G gauge, to drop the voltage there using a resistor converts the voltage to heat. This represents a siginificant load on the signal line. That is not a fire hazard, or anything like that, but it would definately load down the O2 cirsuit to the point that the PCM would be getting false readings. I looked at zener diodes as regulators, but they start at a higher voltage than we are looking to measure, and they drop voltage to the regulated voltage by shunting it to ground, which would rob the PCM of the 2.5 volt offset it is looking for with the real A/F data riding on top of it.

One of the things that I am looking at is voltage copmparator circuits. There were some kits put out by Rainbow Kits that allowed you to build a precision voltage indicator, which provided for customizing it to provide the range you were looking at. The ones I bult a few years ago had 5 LEDs, and you could vary the voltage (or percentage of a maximum voltage)that caused each to light. Unfortunately, this was done with resistance, and was designed to monitor dc power supplies where the current output was large enough that it wouldn't be affected by the small load of the circuit.

There should be a way to make use of the stable, heated O2 sensor(s) present.

The easiest way (now) to get an A/F gauge to work would be to buy a cheap 0 to 1 Volt sensor, weld in a bung and put up with the fluctuations.

The most accurate way would be to use a gauge that could connect to the diagnostic port and translate what the PCM is seeing from the O2 sensor into a precise reading.

Somewhere in between those options should be a solution.
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Old 19 Jun 2003, 02:08 am
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DElight buddy what up!?

I took readings from my o2 today. At WOT at 15psi which i held to redline in 3rd gear, i was reading 3.49V which my guess is that its a rich reading. So it seams safe thuse far. I was at 90 percent duty cycle on the injectors.

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Old 19 Jun 2003, 09:06 am
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Hector,

That looks like it would be a .99v reading on a normal sensor (2.5v offset + .99v reading = 3.49V). That points again to the need to block the 2.5V offset voltage and be able to use the stock sensor(s) on a normal .1 to 1.0 volt A/F Gauge.

I don't knopw if it is worth going after or not. Mopar Performance has said that they will be introducing some gauges soon. They will probably be Autometer, just like the SRT-4 boost gauge.

If Mopar says we have to use another O2 sensor to run their A/F Gauge, then I guess there is not much use in trying to get a usable signal form the stock O2 sensor (wideband, heated and 2.5v offset). On the other hand, if the Mopar Gauge is capable of using the 2.5v offset signal, there will be happy days in the aftermarket.

I still think there may be some merit in the blocking of the 2.5V signal. If you were able to take a reading, and it was near the 1v level at WOT and 90% duty cycle, that in itself says that the signal is strong enough that it could stand a blocking device.

If you want to chance it, put a diode in series with pin 3 (sensor return; what we would normally consider sensor ground - at any rate, it is the "ground" reference for the sensor signal and carries the 2.5v offset)and then check the voltage again.

You can check the voltage before starting the engine. If it reads 1.8V to 2.8v with key on and engine off, reverse the direction of the dioode and try it again.

If you then see .9 to 1.0 (volt range for normal sensor) volts measured under the same conditions, start the engine and carefully check to see if the signal measures accurate as compared to what you saw before. After a slow run-up, and no errors, you could give it a try at the conditions you used above. By this I mean if you would normally be seeing 1.0v on WOT and 90% duty cycle, and you saw 3.49 without the diode, you would be seeing .99v now. If this works, and doesn't cause any MIL to illuminate, all you would have to do to market it would be get the connectors (one male and one female) for the stock O2 sensor and make a Y connector. The center of the Y would go to the sensor, one leg would go upstream to the PCM - via the other connector (no wiring harness cut) and have no mod to the wiring. The other leg would have the diode in line with the sensor return and enough heat resistant wire that a normal butt connector could be used in the engine compartment; away from the extreme heat near the sensor.
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Old 19 Jun 2003, 12:09 pm
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Actually, the simplest way to go about this is to take your a/f apart and change the resistors in it so that it reads from 2.5 to 3.5 instead of .1 to 1v.

I hooked it up to 3 and also to # 4. I forgot which one is what but I got a constant 2.5 on one and the varing 2.5 on the other. With my profect-e01 i can tap directly into the o2 and read the display on the screen. If I knew what the convertion number was, say 2.5 = 14.7/1 then I could type this into my eo1 and it will then display actual A/F numbers on the screen.

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Old 20 Jun 2003, 10:00 am
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If you take the measured voltage. and subtract 2.5 from it, it should give the 0 to 1 volt readings that you are used to working with. The conversions to actual ratio should be correct then.

This is theory only; haven't checked it..

If you change the resistors in the A/F gauge, it may "load down" the sensor output as seen by the PCM, and cause it to dio strange things. Not sure about this, but a thought for consideration.
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Old 04 May 2008, 09:17 pm
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Default Re: About the O2 Sensor

I am having an issue with my O2 sensor on my 05 turbo. I got a check engine light and immediately took it a local shop for diag. They said the alt was bad so I R&R'd it. The light would not go away so I called the dealer (The ones who actually did the Alt R&R) and they said my OS sensor was bad and they forgot to tell me. So I bought a new sensor and replaced myself. I reset the codes by pulling the batt cable and then recharged the batt as well. When I hooked it up bingo everything was good. We drove it for a couple of weeks without a hitch then out of the blue the ck engine light was back on. So I re-read the codes and I am getting the same symptoms. Bad O2 sensor heater control circuit. Code P 0032 So with the engine off and the battery cable disconnected I checked the voltage comparing your readings to my own and I have one difference. I am getting ground readings from two of the four pins on the power side of the loom. I cannot tell which pins due to visual restrictions but it seems to be pins one and four. I do not know what the sensor readings are on the sensor side as I have no schematic to reference. As it stands the O2 sensor issue causes the system to shut down the alternator until I turn of the key and restart the car then it will go a few more minutes and then re light the alt light as well. The ck engine light will not go away under any operating circumstances. Please any help will be appreciated. Sincerely Gary 'Seven Ft' Sauer
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Old 23 Nov 2008, 06:47 pm
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Post Re: About the O2 Sensor

i lake to now with cable off the oxigen sensor is the cable send signal to the computer
heve 4 cable
2 white
1 gray
1 black
an haw mach voltage signal?


tanksssssss
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