Flat lined 02 sensor

I got a cel and some associated codes that seem associated with bank 2 02 issues, I got this simple app that allows a plot of 02 sensor voltages. Top to bottom is bank2 sensor 1(front)' ban2 sensor2 ( rear) , bank 1 sensor 2 ( rear)

All the sensors are about one year old as are the cats. I have another new rear sensor and I suppose I could just put that in but short of the sensor just being shot, what else could it be?

The grey wire is ground, black is signal. In ohming the grey wire feed in the harness to earth I get no continuity. Should this show continuity always or does the ECM control that ground and create the pulsed signals by using it?

The little bumps in the bank one rear to the right on the plot are when I goosed the throttle.
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Bad connection?

 

That's my query. As johnk explained to me in an email, the 02 sensor makes it's own voltage like a thermocouple but it needs the ground as well. So, in my brain it could be a signal wire fault, a ground wire fault, a bad sensor or?..

I was tryingbtomverify the ground wire for starters and got nothing on checking continuity from ground wire on the harness side of the connector to chassis. I gave up,there because that makes no sense unless that's the problem.

 

Bob,

Your B2, S2 flat line is at 0.37 V. That voltage is the voltage between the black sensor lead and what ever the other side (grey wire) is connected to. If the grey wire was open you would just get noise.

Test the O2 sensor with a torch like I emailed you to find it is working. If it is then look for connection problems. One thing at a time.

 

Ok John. If that is so then the ground is OK and the sensor is outputting the .4 v?

Could that just be a default base voltage similar to the 5v we see in the sdecu even if everything is unplugged?

 

I could be wrong. Wouldn't be the first time. But for where I'm standing it looks like a bad O2 sensor. I would either test it or replace it and go from there.

Bob,

One other issue just occurred to me. It could be that the app you are using is not correctly reading the B2 S2 response. Thus that flat line could be bogus.

 

First thing I do is try jump ground 02
s. Attach a jumper from chassis ground to the 02 body.

Yes don't count on the app as bible. Try torque app if you have andriod it's as good as some of the better pro tools. Or some PC based tools are very good today

 

Good point in the app Tim. John just said the same thing to me. I'm going ton throw a positap on the signal line

This sensor has the Brian Crall ground mod on it since last year.

 

Do fuel trims climb when it goes into closed loop? And if so does o2 mv climb or start switching?

 

Not sure what you're asking. The pic in the first post are the voltage outputs of the sensors

 

At what engine temp? Most vehicles will not go into closed loop (using primary o2's for fueling correction) until min temp requirements or run time has been met.

 

Bob, looking more closely at those plots none of the traces make sense. B2S1 0.075V??? B1 S2 0.14V??? Don't know how I missed that before. I guess I was too focused on the flat line. And also, as James asked, was the engine up to temperature? I've been assuming it was.

 

Yes. Engine was at full operating temp.

 

Ok, can you scan fuel trims?

 

Ill see what this app can show tomorrow. Thank ypu

 

Go easy with those positaps, if you break any wire strands you can create an issue down the road. Back probing is a more elegant solution


I was reiterating Johns point on the app

 

John that is a freeze frame of the graph. Those values are changing with the amplitude of the tracings.

 

Ok. But what's the range? Hard to tell without a scale. I was expecting something like this:
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Yes the y axis on my app is not adjustable. I'll play with it in a bit. Looking at some PC based software right now.

 

yes, I see the scale on at the upper right = 0 to 10. So it looks like they might be ok. Just getting paranoid is guess.

 

Just checking the new sensor I have. The body is insulated from the ground wire FYI. So not sure how adding that ground wire to it does anything for the o2 sensors. It might add a distant ground for some other things that use chassis ground but not these sensors

 

I got a much better app. Dash command.

Here are some gauges and graphs. The sensor graph has all four sensors on it. Front sensors are orange and yellow. Rear sensors are purple and blue. Bank2 rear which is the problem one is blue.

I haven't done any further diagnostics other than work with this app.

 

I'm back to my posts 4 and 6, bad sensor or connection. Suspect sensor. Pull sensor and test or replace.

 

Hey John, grab a cup of coffee and watch this vid. Some great stuff in it of interest to our cars.

1) Note the discussion of bias voltage and follow the link to the separate vid on that topic. This explains the .4v on the dead sensor line and also explains the 5v on the SDECU line when all is unplugged.

2) Back testing the signal line on the O2 circuit using the OBD readout and "your body" LOL

3) The early on discussion of the Fords ECU to ignore the bad signal on one side and use the good side for fuel trim. I am going to play with my OBD software and get the fuel trims set up like he had on my layout and see if our cars do the same.

[ame=http://www.youtube.com/watch?v=PYFQ3Y4eFWY]Ford O2 Sensor Testing - YouTube[/ame]

 

Interesting video, but the problem is Bob, you do not have a constant 0.45 volts from B2S2. Your last diagnostic run with Dash Command shows the sensor voltage varying between about 0.35 and 0.41 V. So you are getting a signal. It's just not doing much. The upstream sensor appears to be behaving as expected so this would indicate you don't have a fuel mixture problem. To me it still looks like the downstream sensor is bad.

[edit] I just want to add for completeness that it could still be a bad connections which could cause a voltage drop in the signal. Some there you just have to bit the bullet.