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Below is a non expert test I did some month ago, and it Posted by SWEDECAR [Email]  (#112)  [Profile/Gallery]
(more from SWEDECAR) on Wed, 28 May 2003 09:11:22
In Reply to: o2 sensor replacement success, more info, TML   [Profile/Gallery]
, Tue, 27 May 2003 20:46:24
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doesn't answer the elusive "ground question".
4 wire sensor fuel systems works a little bit different than three wire.
It uses two signal wires to ECU, one is a main signal and the other is a reference signal to double check that everything is fine (sounds like "big brother syndrome" doesn't it?).
The grey wires have a common pin on ECU for front and rear O2 sensor (reference signal). This grey wire might also be the elusive signal ground to ECU but I'm not sure.
The black wire have a oscillating curve that range from 0.4V-1.5V at normal running, and if you close the throttle abruptly the signal drops to almost 0V like all the old sensors.
The Grey wire have an oscillating curve ranging from 0.25-0.75V and also drops down to almost 0V when closing the throttle fast.
The rear O2 sensor works pretty much the same as the front one but the curve is more gentle because of the cleaner exhaust after Catalytic converter, but if you snap the throttle, even the rear sensor max out.
The Grey and Black wires have gold plated connectors.
The Saab electric diagram doesn't list the colors of the O2 sensor wires. I think Saab sees them as being a whole part of the O2 sensor.
But if you use the colors of the connectors up by intake manifold it's listed like this.
Front sensor
pin 1 Grey/white (turns into white on sensor)
pin 2 Black/white (turns into other white wire)
pin 3 Brown/white (turns into Grey wire)
pin 4 Green (turns into Black wire on sensor)
Rear sensor
pin 1 Green/white (white)
pin 2 Yellow (white)
pin3 Brown/white (Grey)
pin4 Green (Black)
Pin 1 is power supply from fuse 38 (this is taken from TRIONIC system 1996 and up)to both sensors.
Pin 2 is ground from ECU to heating element,(two different ground wires from ECU to front/rear O2 sensor)
Pin 3 is low voltage signal to ECU (both sensors are spliced into one wire before they enter ECU).
Pin 4 is high voltage signal to ECU, Front/Rear sensor have it's own pin on ECU (not spliced together as the grey wire is).
What the ECU does is to use both signal wires and compute the average fuel mixture, so when looking at the signal using the Tech 2 scanner, it's only one osccilating voltage curve per O2 sensor and the curve is within 0.1V to 0.8V (just like the 3 wire sensors).
It have been several articles in motor magazines explaining this "2 signal wire system" and caution not to measure voltage fluctuation at sensor wires since the right voltage curve is not achieved until ECU have recalculated the two signals.
Below is another piece I saved about the heater element and different resistance in the two white wires.
(author unknown)
One thing I found while trying to figure out that problem (which turned out to be a faulty inlet air temperature sensor) is that the main difference between the three 4-wire sensors I tried is the heater resistance. I can't remember the figures now, but I measured them and the Bosch 662 sensor that is the correct one for my car has a very low resistance, taking, I think, some 20A of current! The 574 sensor (an earlier spec, I believe) drew substantially less and the generic sensor (made by Williams and distributed by ScanTech) drew very little.
The thing to note here is that fitting the 662 sensor to a vehicle requiring the 574 sensor would likely result in a blown fuse.
I assume the later sensor is designed to heat up more quickly to meet stricter emissions regulations (way beyond anything required here in the UK).
(part answer from another author unknown)
Saab 4-wire O2 Sensors have 18W heaters. The heater resistance is 2 ohms at room temperature. The higher-power heater is necessary because the turbocharger removes a lot of the heat from the exhaust gas that a normally-aspirated engine produces. The generic sensors generally do not have this 18W heater.
As to make it even more fun for the future, another type of O2 sensors are on the way and they too have a different scope.
Have fun
Anders
posted by 67.113.8...
, Tue, 27 May 2003 20:46:24, Wed, 28 May 2003 09:11:22 <-- Viewing This Message, Thu, 29 May 2003 20:43:10, Wed, 28 May 2003 08:00:18
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