Bad Knock Sensor With Significantly Improved Fuel Mileage

Any comments/explanation to explain this odd observation is much appreciated.

Background: On May 25th, 2012, under the Recall Campaign 11E-A03, dealer replaced EGR valve and programmed the control units with CAS. SA told me for my model the SCR mixer didn't need to be replaced. After this EGR replacement fuel mileage dropped approx. 1 mpg but otherwise the car ran just fine, no codes whatsoever.

On Oct. 16th, 2012 when I took the car in to fix a window noise SA told me BMW is now asking they also replace the SCR Mixer unit. Got the car back and everything was fine.

Relevant portions of the work order are attached for both replacements.

Last Friday (ten days after SCR Mixer was replaced) I got the CEL - my scanner read the OBD2 code as P20EE (SCR NOx Catalyst Efficiency Below Threshold Bank 1). I emailed my SA right away and dropped the car off the next day. I also told him about the OBD2 code.

Before I left the house to drop the car of at the dealer I reset the mileage meter. My drive to the dealer is about 30 miles, mostly highway. My mpg read 27.2 mpg! I have never seen that high a mpg number. Since the EGR replacement my mpg was ~22.7 mpg. (I have the 3rd row (added weight) and Option 214 wheel/tire.)

Two hours later my SA called and said the knock sensor was bad and needs to be replaced.

Questions:

1. SA thinks faulty knock sensor and SCR Mixer replacement events are just coincidence, not related events. I find that hard to believe - comments?
2. OBD2 code for knock sensor are P0325-P0334 (based on a simple Google search) - can P20EE I read also be related to knock sensor? Since the work is not completed I don't know the OBD2 code the dealer tech read.
3. Assuming I have a faulty knock sensor, shouldn't the mileage go down - I experienced a dramatic increase, almost 20% better! How can this be?
4. Can a SCR Mixer replacement cause a knock sensor to go bad? I find it hard to believe it is just a coincidence.

My explanation - using logic and imagination and no experience with such things - the programming that was done after the SCR Mixer replacement somehow turned off or partially shut down the emission control. This explains the 20% fuel mileage improvement. This programming may also have corrupted the knock sensor readings. Does this sound possible/reasonable?

I would sincerely appreciate if someone experienced can explain what I am seeing - P20EE error code, significantly improved mileage and dealer tech's claim the knock sensor has gone bad.

Thanks.

PS: Jim E. post describing this emissions recall in greater detail.

Excellent post.

The faulty KS is strange...usually a bad KS will do a few things: Set a code, trigger a CEL AND... pull timing to protect the engine. You lose 5-10% gas mileage.. All this based on general experience, not X5 or BMW. So this is opposite what you are seeing...


From what I've read and heard, the 'programming' they do is pretty damn bulletproof- there arent corrupted stuff floating about. Once the car completes the load and everything is verified, your car basically has THE program they intended....now BMW can write/release bad code- or code that doesnt contemplate the physical conditions of the sensors and components (which was what happened for months on end with the 2010s and resulted in the string of recalls).

For me, the most likely piece of bad info is what the SA is telling you...wait for them to put it in writing and talk to the tech before you drive off, if you want the real story....

A

Thanks ard!

What you wrote is what I was expecting - code could be due to a bad KS or a transient software error. If it is the former there should be a drop in mpg, if it is the latter no change in mpg. IMO a 20% increase 'may' occur if somehow the emissions got shut off - not a likely scenario.

The other thing that surprised me is the tech did not read the code I read (P20EE) . . . instead he read a bad KS code which Google Search says ranges from P0325 - P0335. I can understand BMW tech with a better scanner reading more codes than my simple reader . . . but I don't understand why he doesn't read what I read.

As you said what the SA is saying and what the tech is going to write may be two different things.

Yes I will post my service report once I have the car back plus what the tech told me he did.

Thanks again.

Originally Posted by ard

Excellent post. . . . .

For me, the most likely piece of bad info is what the SA is telling you...wait for them to put it in writing and talk to the tech before you drive off, if you want the real story....

A

ard, you hit it right on the money . . . this was a case of comical mis-communication! Over the phone I heard the SA telling me they need to replace the "knock" sensor . . . what he actually said was "NOx" sensor! Now that makes a whole lot more sense! Agrees with the code my scanner read.

I met with the tech and he told me the codes they read (see attached) required them to replace the NOx sensors. He didn't think the SCR Mixer replacement and this sensor going bad was connected, just a coincidence - at least that was his best guess.

He has no idea why my fuel mileage improved by nearly 20% (from ~22.5% to over 27 mpg!). On my way back from the Dealer my mpg was about 24+ mpg (mostly hwy) . . . still higher than what I saw after the initial EGR valve replacement and associated re-programming. I will keep an eye on the mpg for the next several weeks and see where it finally settles. Since mpg is moving in the positive direction I am not complaining!

That actually makes one chuckle... NOx sensor is really a new term for most of us...

You really need many days of use over the same commute to make hard mpg comparisons.

Yes I need more time to confirm which way (if any) the mpg moved . . . typically I try and do it over three or more tanks (1,500+ miles) . . . my mpg prior to the original EGR replacement was ~23.8 mpg . . . post EGR replacement it dropped to ~21 mpg and then picked up to about 22.5 mpg. Let us see what happens after this latest service visit.

Got the CEL again after doing a long weekend trip - ~1,100 miles, which included hwy and city miles plus mountain climbs to about 8,200 feet. Same OBD2 error code (P20EE) - second time over a month period.

Here is a brief summary of the events since the original EGR recall.

• Per the original recall EGR valve + programming was done
• About a month back SA told me I also needed the mixer replaced - this involved mixer + programming
• Two weeks later I got the CEL - they replaced the NOx sensor
• A week later I got the same OBD2 error code (P20EE) . . . this time I told the SA most likely the hardware is fine, software must kicking out these error codes . . . and replacing parts most likely will not fix this issue. Tech agreed with my reasoning but said he has to follow the procedure dictated by BMW

Following is what the tech told me after completing the latest repair work.

• They replaced the catalytic converter - see attached for work performed
• Tech admitted on a few cars after the last re-programming they are seeing cases where catalytic converter needed to be replaced.
• Tech said - it appears the new programming is more sensitive than the previous one - and this "might" be the issue - i.e. old programming was not this sensitive
• The new catalytic converter has a new part number - this could be due to some design change and/or catalyst itself is different. Tech doesn't know what the changes are
• So far cars that got the EGR and SCR Mixer replaced + the latest programming + new catalyst have not come back with CEL . . . too few cars have had all of this done, so too early to say this problem is fixed

I continue to be impressed by the customer service Kevin/BMW Concord is offering . . . no BSing, where they don't know the answer they simply admit it, honest about the limitations BMW places on them, etc etc . . . on this visit, since they had to test drive it much longer than normal, they gave me a full tank of diesel - nice touch!

I will post if CEL pops up again . . . will be driving about 1,000+ miles over the Thanksgiving weekend.

As always if others have had similar issues please do chime in . . . I am skeptical this issue is fully fixed . . .

BTW this car is a blast to drive on those deserted twisty mountain roads - I was hitting 70+ miles on those curves, worked the brakes really good . . . I could have never done any of this on my previous SUVs! With AD it would have been an even bigger blast! Oh well . . .

They must enjoy working with you. I am dead serious. I can be a PITA here, but with my SA it is much different. It makes it easier.

Anyway, you SHOULD get a work order and code pulled if you can..at least to get it on the record. Even bringing it in and waiting for them to read and clear it, if all they say is "see if it comes back".

Although, back to the first point, pushing for this before T-day is a bit much.

Thanks for documenting

A

Thanks for your post.

Not very familiar with these terminologies . . .

• "pulling code" - this is printing out the *history* that is stored in the car - right? Related question - does the tech clear the history after the repair is finished or is the history permanent and not delete-able by the tech?
• history is different from the listing of error codes generated - right? . . . error codes get deleted once the repair is performed - right?

Given I am not someone very familiar with all of these issues I have to go by logic . . . and my logic runs as follows:

• Car was running just fine until the SCR Mixer and related programming work was done. (IMO the car would still be running just fine if this work was not performed)
• I don't think the first NOx sensor replacemnt was necessary - i.e. I doubt it was really a defective sensor. That said, it is unclear to me why the 4D16-SCR didn't show up the first time
• I was very surprised the catalyst had to be replaced - at 40,000+ miles, that is less than half the expected catalyst life - right?
• One possible explanation for catalyst replacement - the new software has tighter specs than the old one, meaning the catalyst has to be more efficient . . . new catalyst has a different part number which could mean the catalyst material itself is different and its efficiency is sufficient (hopefully!) for the new software. Yes my logic is a bit of a stretch . . . if CEL doesn't back on I am happy to go with this logic!

I empathize with the tech - if he is pulling a fault code 4D16-SCR I am assuming he has to follow the solution dictated by BMW - right?

If I asked the dealer to "pull code" for me under a work order with the car showing no CEL or any other issues - who will pay for the labor? I doubt the dealer can make a warranty claim since the car is working fine . . . just curious.

Now if I have to go back in a third time for the same error code my scanner reads (P20EE) then I have a legitimate claim (IMO) to escalate this matter. I hate to beat up on folks who appear to be doing what they are expected/supposed to do.

As mentioned previously over the Thanksgiving period I am planning to put ~1,000+ miles - that should be a solid test to see if this latest fix holds.

Post Thanksgiving I will post whether I got the CEL or not.

PS: While trying to understand what 4D16-SCR I came across this post by ard and others . . . for those trying to understand this issue better, it is pretty good/quick read. Info is a bit dated - i.e. it may not apply to MY2011/12 cars . . . many fixes might already be in place.

I quit posting some time back. But your post brings back some memories. Here's my experience with a 2011 X5 35D (too delivery late May 2010 - you can look for my posts)

1. 09 Jun 2010: Trunk lid will not close. Mileage ~230. Dealer replaced trunk lid lock
2. 21 Apr 2011: CEL on. Mileage 5700. Error codes 4D16, 480A. Diagnosis/work says "performed DEF regeneration by driving. They basically cleared the codes and gave back to me.
3. 28 Apr 2011: CEL on again along with low DEF warning. Mileage ~5800. Error codes 4D16, 4BD3. Replaced DPF (Diesel Particulate Filter), Exhaust Manifold, SCR Catalytic converter. Refilled with DEF.
4. 18 May 2011: CEL on again along with low DEF warning. Mileage ~6300. Error code 4D16. Catalytic converter permanent malfunction. R&R Catalytic converter.
5. 21 May 2012: CEL on. Mileage ~13500. Replaced charge air sensor, EGR valve (campaign).
6. CEL returned after 30 miles from dealer. Wrote letter to BMW NA.
7. 21 Nov 2012: Wrote letter to BMW NA, CMRRR
8. 07 Dec 2012: Mileage 20000. BMW NA sent Regional tech rep. Dropped off car today. As per write-up, SCR Mixer, Reprogramming and Bolt replacement to be carried out. SA called a few minutes ago and mentioned that they have to replace the NOX sensors as well.

Already consulted/retained a lemon law attorney and that process is already under way.

Originally Posted by acrackl

I quit posting some time back. But your post brings back some memories. Here's my experience with a 2011 X5 35D (too delivery late May 2010 - you can look for my posts)

1. 09 Jun 2010: Trunk lid will not close. Mileage ~230. Dealer replaced trunk lid lock
2. 21 Apr 2011: CEL on. Mileage 5700. Error codes 4D16, 480A. Diagnosis/work says "performed DEF regeneration by driving. They basically cleared the codes and gave back to me.
3. 28 Apr 2011: CEL on again along with low DEF warning. Mileage ~5800. Error codes 4D16, 4BD3. Replaced DPF (Diesel Particulate Filter), Exhaust Manifold, SCR Catalytic converter. Refilled with DEF.
4. 18 May 2011: CEL on again along with low DEF warning. Mileage ~6300. Error code 4D16. Catalytic converter permanent malfunction. R&R Catalytic converter.
5. 21 May 2012: CEL on. Mileage ~13500. Replaced charge air sensor, EGR valve (campaign).
6. CEL returned after 30 miles from dealer. Wrote letter to BMW NA.
7. 21 Nov 2012: Wrote letter to BMW NA, CMRRR
8. 07 Dec 2012: Mileage 20000. BMW NA sent Regional tech rep. Dropped off car today. As per write-up, SCR Mixer, Reprogramming and Bolt replacement to be carried out. SA called a few minutes ago and mentioned that they have to replace the NOX sensors as well.

Already consulted/retained a lemon law attorney and that process is already under way.

Please dont give the atty a dime more than you can get from BMW.... while BMW pays the legal fees, most lemon law scum charge you a % of your payment too. You are wasting money if you pay them a contingency.

If this was in CA, and you achieved the number of visits or 30 days to qualify for a lemon buyback, the good news is they % they use would be about 5800/120000 or 4.8%. You would receive 95.2% of your purchase price back, given that the issue first started at 5700/5800.

So make sure you understand the law in your state.

A

Ard, The manufacturers are 100 steps ahead when it comes to lemon law - wish I had known all this before hand. There is a reason the service orders are written a certain way - "Customer states that CEL is on" for example. Then there are rules like it has to be the same problem - well the manufacturer can argue that the CEL was caused by different problems. Plus I live in TX,a pretty business friendly state. I didn't want to go this route - with an attorney, but BMW N.A just ignored me. It appears that they just want to keep this thing stringing along and hope the customer just goes away and does nothing. I didn't have the same experience several others mentioned where they said BMW just stepped up. Even though they are called lemon law attorneys, they are filing under DTPA (Texas Deceptive Trade Practices Act) - which has a fee shifting provision.

Originally Posted by acrackl

Ard, The manufacturers are 100 steps ahead when it comes to lemon law - wish I had known all this before hand. There is a reason the service orders are written a certain way - "Customer states that CEL is on" for example. Then there are rules like it has to be the same problem - well the manufacturer can argue that the CEL was caused by different problems. Plus I live in TX,a pretty business friendly state. I didn't want to go this route - with an attorney, but BMW N.A just ignored me. It appears that they just want to keep this thing stringing along and hope the customer just goes away and does nothing. I didn't have the same experience several others mentioned where they said BMW just stepped up. Even though they are called lemon law attorneys, they are filing under DTPA (Texas Deceptive Trade Practices Act) - which has a fee shifting provision.

If you read many of my posts, I tend to harp about 'force the SA to write up the complaint this way', combined with "dont accept the car back unless they provide written confirmation of the codes and problems". I do this many times starting with the first complaint, and I am sure people thing "man, this guy sure makes it complicated...I just want my car fixed, I dont need to know whats wrong"... so they dont, they hope it will be OK...but after 2,3 visits, it becomes clear that they've wasted their time and now the dealer is circling wagons and they have no record.

People just sit at the desk and let the guy type what he wants, then they hand you a pen and you sign it.... I just got back from the dealer an hour ago, earlier today I wrote "No permission to operate vehicle off dealership property." next to my signature. The SA was very nervous. I said "Dont worry, I can do this" and smiled. (CA has a law that they MUST check and adjust the tire pressure, unless the owner states he has done that. So I crossed that out on the work order and added "Owner has checked tire pressure within last 24 hours".) My point is that it is YOUR car, this is a document FROM YOU telling them what they should or may do....

Anyway, just briefly looking at your record, those initial codes are all relating to the diesel cat/emissions system and are central to the recent recalls...using their own documents on the recall, I am pretty sure you could have argued that the common cause was this system and the underlying software, was the problem. As a result there were multiple spurious error codes and ineffective repair measures which were the actual cause of the lemon claim. I mean it looks like your issues were a poster child for the final, ultimate recall they issued! You had all the issues that kept cropping uo; BMW engineers would run 'diagnostics' that were flawed; they'd replace the wrong parts; and different problems cropped up. They finally figured this out, with a major recall that had a 'menu' of fixes, depending on what they'd tried on your car already.... .

I am surprised that you met the lemon criteria, provided the evidence, and gave them a written demand and they ignored it.... yes, they will tell you "oh, we replaced different parts each time", but the trick is to build the trap early on- and argue that this vehicle is affected by the core diesel emissions fault...

And also, the dealer is a major factor in the success of a lemon claim- if your SA or manager or warranty manager at the dealer says "yeah, this car is a mess, we agree", then BMWNA lemons it. If the dealer is a dcik, BMWNA says 'tough'.

Keep us posted...

A

Quick update . . . put in over 1,200 miles after the catalytic converter switch . . . car performed like a charm. This drive included several ascends and descends (over 8,000 feet) . . . had zero issues. Only problem the front brake pads wore out (it was on the raggedy edge) . . . upon our return dealer replaced pads and rotor.

On those twisty roads - it was pure pleasure to drive this car!