Sanity Check -- Sudden Lambda sensor issues after expansion tank replacement

[ryushe]

Preface: N52 - 3.0si, replaced all 4 of my lambda (oxygen) sensors a couple of months ago, both pre- and post-cat ones. They're brand new Bosch sensors, and seemingly wired correctly.

About a month ago my cooling system expansion tank broke (associated post for those interested), which has since been replaced. Sadly couldn't do the work myself due to an ongoing wrist injury so had a local indie shop take care of it, as it's an easy job as it is. Dropped it off in the morning, and when I picked it back up later that day the first thing I saw was a CEL in the dash. Mentioned it to the mechanic, and as I don't always keep a scanner in the car all the time, he checked and cleared it for me on the spot. He was too fast and I never saw the error code.

Now before I dropped it off, the last time the CEL came on was what prompted me to replace the lambda sensors. Haven't had issues since then, no faults, no warnings, no issues. Ever since picking it back up I'm getting intermittent faults (P0041, P2195, P0132). Car runs just fine, and after scanning and clearing the faults they stay away for a day or two. I'm not the most mobile at the moment, so have done a cursory check of the wiring and everything seems OK.

So here's the sanity check question; On one hand this seems like a bit too much of a coincidence (everything fine before tank replacement, faults after replacement). On the other, this could of course actually be a coincidence and there's indeed something going on with the lambda sensors.
Either way, before calling a shop again to troubleshoot, I'd like to get your opinion on things.
Suggestions?

 

[bigwinn]

If it was me I’d give it time to see if the eml represents itself

The sensors don’t like knocks so that may have caused them to show

 

[j3nks79]

The expansion tank is nowhere near any of the sensors or wires.
You have another issue. Maybe gasket leaking from down pipe to mid section.
Or the heating elements are playing up on the sensors.
Or intake leak. Etc etc etc.

 

[ryushe]

If it was me I’d give it time to see if the eml represents itself

It does. When cleared while running it stays off, but there seems to be a 50/50 chance of coming back on when I start the car again. Have seen and cleared it a couple of times by now.

 

[ryushe]

The expansion tank is nowhere near any of the sensors or wires.
You have another issue. Maybe gasket leaking from down pipe to mid section.
Or the heating elements are playing up on the sensors.
Or intake leak. Etc etc etc.

First point, that's what I was thinking. There's no way they physically did any work even remotely close to the sensors/wires.
Your third point is interesting, as faults P2195 and P0132 both have a description that starts with "Heated oxygen sensor (HO2S) 1"
I find it interesting the other fault P0041 mentions swapped sensor signals...
And thanks for the other points, certainly things I can investigate / have investigated.

 

[j3nks79]

Does sound like the heated elements have failed in the sensors.

 

[Mike6]

I had a specific code for the heater element in the lambda sensor on bank 2 post cat. Had both replaced by my local garage but
Now getting a code for oxygen enrichment on both banks.
Seems to suggest an air leak on the induction side but have stripped everything out and definitely no air leak
I am now leaning towards the seal on the lambda sensors as old ones had to be burnt out or possibly an air leak on the exhaust joint where the sensors fit .
I would suggest therefore that one or more sensors could be letting a bit of air in and need refitting with a bit of exhaust paste and or the exhaust joint be remade with some exhaust paste.