Here's what I copied, and emailed to myself about it. It seems there may be some more updating from Ford needed. I'm waiting to hear more before taking mine in.
Repeat NOx MIL P164A DTC & TSB/SSM
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I've been waiting before I chimed-in here regarding the repeat NOx MIL DTC P164A pending having some definitive information regarding the issue since the trans-shift calibration update was released. From what I've been able to discern, talking with engineering and our product concern engineers, there appears to have been three (3) variables in play. The SSM that was recently released (3266 - 6.7L DIESEL - DTC P164A RESETTING AFTER TSB 11-04-21) is an attempt to provide a course of action for Dealers to follow that will allow to correctly diagnose the repeat MIL that some of you have been experiencing. Below you will find a summary of the sequence of events that will hopefully provide some closure.
Apparently there was a disconnect in TSB 11-04-21 and it's limitations in addressing P0164 in that due to the nature of the concern, the TSB would address "some" of the NOx MIL issues under a specific set of operating conditions. The primary task of that TSB was to address shift quality while also tweaking a few other parameters of the calibration to address certain operating conditions that could trip a MIL. However, those limitations and the communication of the information to the field/dealers may have been somewhat confusing as there were more than one root cause for the initial complaint of repeat MIL/DTC P164A.
As some of you have come to know, there are trucks that have needed both the NOx Sensor replacement along with having the calibration updated. The third piece or variable that has come into play is that the adaptive NOx table reset process to force the adaptive tables to adjust to align with the new NOx sensor output and calibration change requires what I can only describe as excessively labor intensive. Based on the dialog I've had over the last couple days with the calibration folks and powertrain, I'm not the only one that acknowledges this and there's a full court press to address.
In my attempt to provide some of the details, please be aware that due to the nature of the overall system and the sensitivity of the components involved, if the procedure is not performed and verified correctly a repeat NOx MIL and DTC P0164 may reset. Those involved (my apologies to those here participating on FTE) are acutely aware that this has caused major frustration from both the Owner's and the Dealer/Technician service side.
From the communications that I have had, SSM-3266 is the initial stop-gap measure to address those vehicles / customers that have had repeat MILs caused by DTC P0164. Engineering has been working directly with 7 vehicles/customers here locally with 5 having been confirmed fixed with the other 2 working through the logistics of getting them in to be serviced as they are currently in use as work trucks. There will be further actions in the future to improve the lengthy process that's involved to verify that the NOx system is operating within it's nominal range.
Considering all the sensitivity and frustration around this repeat MIL issue, here's a summary of the facts as I know them, what has transpired and next steps. Back before the end of the year, engineering was made aware of the P164A NOx codes being seen the in field. Initial investigation saw the need to modify the calibration parameters for certain operating conditions and release a calibration update. After the calibration update, over the course of another month or so, the engineering is still being advised by the product concern team that we're still seeing P164A / MIL issues. Knowing that a calibration change had been made to address the issue, engineering initiated another investigation of the issue and determined that some NOx sensors were showing sensitivity variability from part to part. The sensor supplier was then contacted and made aware of the findings. The supplier then initiates their own investigation to substantiate those findings.
The end result was that under the right conditions the NOx sensor manufacturing process would allow for internal contamination of the sensor. The manufacturing process has since been changed, now using laser welding vs. spot welding. Engineering is/was convinced that when a defective sensor is replaced with the new part and/or a calibration update (revised again for TSB 11-04-21) that the NOx / P164A MIL issues should be resolved. That brings us to today (early last week actually) and we're still seeing NOx / P164A repeat MIL/DTCs being set. Engineering, under pressure from most every customer touch point in the company looks again at the code in the powertrain control module. What's discovered is that during the NOx table reset process using IDS, that the table reset acknowledgement is being communicated from the powertrain control module back to the IDS tool as being completed when in-fact it had not been reset. Thus even if you updated the calibration and/or replaced the NOx sensor, there was considerable risk that another repeat MIL/P164A code event would occur depending on the failure mode and how far the NOx table had been offset. The Dealer or Technician would not know that the table wasn't reset or that a repeat MIL was likely under the right conditions.
The SSM 3266 was released to advise that multiple NOx table resets may be required to truly reset the table. To be sure, the sensor data and min/max table data needs to be viewed during several zero pedal coast-down events from 50 MPH to fall within a specific range. I suspect in the near future, a calibration revision will be forthcoming to modify the NOx table reset function. I know this has caused quite a stir here on this forum between a number of the members and I truly hope this helps put some of that to rest. It's one of those issues that had many tails to it, several failure modes all resulting in the same basic MIL/ P0164A DTC.