Shouldn't my post-cat O2 sensors (lambda probes) be reporting varying numbers?

Question

On my 2002 BMW E46 330Ci, I've been getting error codes 202 Lambda regulating limit Bank1 and 203 Lambda regulating limit Bank2. Here's the angry sensor readings from the INPA software:

I understand a number of things could be going wrong here, but tonight's discovery has been that the actual readings on the post-cat lambda probes are sitting unchanged at 0.42 whilst the engine runs and I rev the engine. Conversely, the probes pre-cat are varying substantially:

These were taken whilst the car's engine was warm, but not right after or during a substantial drive.

If necessary, I can post a video of the readings, but that's the gist of it - pre-cat O2 sensors are fluctuating substantially whilst post-cat sensors aren't at all. It's interesting that they're both sitting dead at 0.42.

Does that mean my post-cat sensors have failed and need replacing? Or is this some incredibly accurate tuning by the geniuses at BMW!

Hot idle readings

I just took my car for a quick drive to get the engine temperature up to the operating level, and have the following readings via INPA software:

Did not clear errors prior to drive/readings

Interestingly, the lambdaintegrator readings are now within the expected ranges with flat zeroes.

I've taken screenshots of the rest (digital, throttle, VANOS, roughness etc) but I don't think they'll be helpful so haven't included them so far. If the above readings are also still too much, please advise, though I think they should all be useful.

Answer 1

Here's how to decipher INPA

• lambdaintegrator

  Short-term fuel trim. Both banks have a short-term correction of 28%.

  This should settle down to 0% fairly quickly, so the fact that it stays red indicates that it is attempting to apply the maximum possible correction for a lean condition (and failing to bring it within spec).

• adaption value additiv

  This is an aspect of long-term fuel trim correction that becomes dominant at low loads.

  Unless the fuel trims were reset prior to taking the screenshot, there is something preventing LTFT corrections from being applied.

• adaption value multiplicativ

  This is the second half of LTFT correction that becomes dominant at high loads. It acts as the chief injector pulse width multiplier.

  Same comment as above; it is not being updated for some reason.

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Based on the update (26-09-2016)

MAF, Idle Air Control

• Mass air flow looks good; my 5.0 L S62 reads about 19-20 kg/hr at idle, so a 3.0 L engine should display about 60% of that value, which it does.

• I don't see anything funky going on with idle air control. Hard to say anything about the knock sensors from a still image.

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Fuel Trims

• This output makes a lot more sense than before. Perhaps you had reset the fuel trims prior to posting the original screenshot?

• There is a minor positive fuel trim correction on both banks; the fuel trims are normal and healthy - not hitting any limits

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Error codes

• This is interesting. The errors are sporadic, so it looks like the conditions that triggered the error occurred 9 times and 7 times for Banks 1 and 2 respectively. At least one of those conditions on either bank was when the car was still warming up (coolant temp at 74˚C).

• I'm concerned that the heater circuits for the front O2 sensors are still active, despite the car being at hot idle. This should not be the case.

• Also, the resistances for the upstream O2 sensors (pre-cat) are unusually high; they should be closer to 5 Ω. I think your upstream sensors are shot. Were they ever replaced under your custodianship? If not, I think it's time to invest in a pair.

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Recommendation

• Replace the front O2 sensors. You can use this answer to test their present condition. It may be worth your while to check the condition of the rear O2 sensors as well while you're at it.

Answer 2

It may depend on how you are gathering that data. Perhaps a "Live Data" OBD Parameter ID or "PID"?

You may need a more specific scan tool or smarter software.

Some (especially higher end) vehicles use wide-band O2 sensors, and on my scan tool read out in milliamps, not in volts.

In other words, your scan tool may be looking at the data the wrong way, or in the wrong place.

Also, keep in mind that the cat (and downflow sensor) need to be really hot to give any meaningful data. If your scan tool setup is portable, I'd suggest some observations while driving.

Answer 3

I had the same trouble code from O2 sensors like above. It's not the sensors that have problem. It's just telling you, it's trying to compensate for F/T mixture but it was unable to due to the fact it had reached it's LIMIT for compensation.

I tried a lot of other testing, finally it is the air leak that caused that problem. Mine was when I replaced the Cover Valve Gasket and it was not sitting correctly therefore I had huge vacuum leak. I did a smoke test and found out the problem was the cover valve gasket was NOT sitting properly, fixed that and smoke test again and no smoke. Clear the code, started engine, and no more problem. Don't replace O2 sensors for this problem. I've been running for 2 days without any problem, and INPA showing Petrol Adaptation is back to normal 1-2, instead of 28 like before and the engine is smooth now.