DME: Trimming, oxygen sensor before cat., Bank 2
 

After searching the forum and having found numerous threads about it, I'm totally confused. I hope someone can help me with this. I have a 2006 3.0 that just started throwing the code above. I've cleared it a couple times and it comes back. So I opened up the OBDII and got the live data. The live data is below. I hope someone can tell me what I'm seeing.

Load PCT: 5.5%
ECT: 203F
SHRTFT 1: varied between -1.6 to -3.1%
LONGFT 1: 6.3%
SHRTFT 2: varied between 0 to -3.9%
LONGFT 2: 7.0%
RPM: varied 774 to 781
Spark Adv: varied -2.5 to -3.5
IAT: 151F
MAF: .01lbs/s (calculates to 4.54 grams)
TP: 9.8%
O2B1S1: varied .130 to .730V
SHRTFTB1S1: varied -1.6% to -3.1%
O2B1S2: varied .750 to .770V
SHRTFTB1S2: 99.2%
O2B2S1: varied -.135 to .750V
SHRTFTB2S1: varied 0 to -3.1%
O2B2S2: varied .720 to .750V
SHRTFTB2S2: 99.2%

Thanks for any help you guys can provide. I'm not even sure where to start.

O2 can't range to negative values. The precat if reading negative values something is wrong. Looks like a case of problem sensor.

Also: post cat should gravitate to 0.45V so the 0.75 is very high but that can vary a lot.

What I would do: reset all the sensors by unplug them all, start the car run until you get multiple errors (probably missing O2 heater error) then plug them back in and clear the codes.

See if the numbers will come back into normal range (0.1 to 0.9v).

If you get values outside of normal you probably need to replace the sensor (use OE or OEM don't cheap out: I need to replace my knock off sensors)

I should have said I recently replaced all of my O2 sensors using Bosch replacements.

So if you are getting out of possible range it's either a bad sensor or problem in the ECU. The easy test is swapping the two pre cat sensors and resetting adaptations (or as described above recalibrate the DME)

I just tried recalibrating the DME and resetting adaptations. No change.

I'll try swapping the sensors this weekend if the weather cooperates.

Swap the pre cat sensors and see if the problem migrates. It feels like a bad new sensor to me.

I'll try it. I hope that's all it is. FCP will replace it for free!

Actually, for Short term fuel trim or long term fuel trim the value can be negative or positive. Negative STFT will mean that the DME is taking away fuel and positive STFT will mean the DME is adding fuel to the mixture.

The post cat 02 voltage should be at a constant value whereas the pre cat 02 sensor the voltage will vary.

Here's a video on 02 sensors as it relates to voltage

https://www.youtube.com/watch?v=zyh_4SktmFM

Here's a video on STFT vs LTFT. You can see that the STFT is negative because the LTFT is positive and the DME is trying to zero out the fuel trim.

https://www.youtube.com/watch?v=WMSM7WAbBss

Trim can of course be pos or neg. O2 reading can't be negative.

https://uploads.tapatalk-cdn.com/201...97e730c1ee.jpg

Is that an actual print out from the OBD II scanner or is that just a typo on the part of the OP while he was preparing this thread.

If you viewed the video that I posted you will see that for the voltage on the 02 sensor (actual screenshot of Torque Pro live data), starts at 0 and goes from there. It can not go into the negative value. It will be the same as if you drove your X in reverse and the speedometer will read a negative value which we all know it doesn't.

It was showing a negative value.

I don't even know how that's possible to even display much less have an actual negative value. Cross talk from a near-short. If the number still shows neg on the same sensor I would take the DME out and open and clean the traces. I have a photo with the traces that go to the heater controllers: some gunk on the traces or some gunk in the connector could cause an odd reading like that.

What type of scanner are you using?

Schwaben. Same as the Foxwell.

Update
 

After previously posting and doing a clearing of adaptations and DME re-calibration I was still getting the same readings off the OBDII. So, I did the adaptation clearing and DME re-calibration again, this time being very careful to exactly follow the procedures directed by the scanner. The SES light has not returned. A scan of the OBDII is now showing what looks more like normal readings that would be expected. I think I may have solved my problem. Knock wood.

ME aka Mechanic Error.

Yep

I had same problem/ish and did the same and it worked for like six months and came back. I'm suspecting i now actually have a vacuum leak or bum MAF. I'll probably finally make/rent/buy a smoke tester and if no smoke, i'll swap MAF back from wife's car to see if there is a change.

I did notice in my case that six mo. ago when i originally did like above and swap MAF with wife, the fuel trims were more like +6, ±1% (short/long) and now there are both showing like +5 +7, so the computer is definitely seeing too much air or too little fuel.

what are your fuel trims now showing? if the long term is close to zero i think you're golden. I think i just acquired a new vacuum leak not the same problem returning.

PS: if you don't have a tool with you to do adaptation reset, My original trick of unplug all O2, start the car a couple times, the plug them all back in seems to do the same function; even with my car running fairly lean (+7% long term), the error didn't come back for about 100 miles.

Wouldn't a vacuum leak throw a code?

Short terms are variable. -3 +/- to -4 +/- Long term steady at +7

Yep sure does. Im getting a code within 10-50 miles after reset. I think it's actually MAF or an intake leak.


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I think my lean codes mystery was solved last night when my fuel pump died. Hard failure just stopped while driving.

After it stalled I poked the fuel rail valve with a screwdriver and didn't even get a splurt.

The weird part is I thought I could hear the fuel pump hum but perhaps just too slow to generate any pressure.

Going with OEM brand this time. Knock off didn't last a year. I realized after I already had the knock off, so been mentally prepared for a while.

Funny thing is I actually thought to myself "if I don't have a vacuum leak, low fuel pressure will also cause a constant state of lean".