OBD11 Error Codes PO171 and PO174 - BMW M5 Forum and M6 Forums

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Old 9th February 2007, 20:22   #1
jgillon
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OBD11 Error Codes PO171 and PO174

This is my first post so please forgive me if I forget to add something here. Let me start with information about my M5. It is a 2002 with 40K miles on it currently. I am the 2nd owners and I bought it with 30K miles. Since I have purchase it I have done the following upgrades. Dinan - Clutch, Lighten flywheel, Short shifter, Cold Air Intake, Stage Two Software, and Front tower brace. I donít think this information matters but I want to give as much information on my car as possible.
So now to my problem. About one month ago I took my car in for a service two. About one week after my service my SES light came on. I was in the area of my service shop and took it by. They said the service light was due to a bad MAFS. They gave me a couple of chooses of MAFS (either the OEM or the VW MAFS that I found on the message board as an appropriate replacement). Both options seemed a little pricy, but lucky I have a friend who works for a dealership and hooked me up for $130 for the two MAFS from VW. I installed them and the SES light continued to come on. I then went back on the message boards to see if I had missed something and thought maybe it could be the pre cat 02 sensors. I then proceeded to replace them as well. In the process I picked up a Peake Reader and OBD11 scanner. Well to my dismay the light still comes on. The freeze frame data states the following information on my last SES light.
Fuel Systems 1 and 2 Closed Loop
Load Value 24.3%
Coolant Temp 183*
Short Trim Fuel Trim bank 1 is -12.5% bank 2 is -13.3
Long Trim Fuel Trim bank 1 is .8 banks 2 is .7
Engine Vehicle Speed 18 RPM 1965
MPH
The problem always occurs after the car has been running for 20-30 minutes. For example the last time it went off I was sitting in traffic.
I have been told that it could be an intake leak, but I have checked all of the hoses and I have seen nothing. Plus if that was the problem would it be a problem all the time?
If any body has any ideas or can give me direction on what to look for that would be help.
Thank you
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Old 10th February 2007, 00:08   #2
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i a bit confused, what are the peak codes? the obd 2 data doesn't really show any faults that i see. The coolant temp, are you quoting it in F degrees?

I don't know what codes po171 and 174 are.

You need to know what the fault codes are, and replace the appropriate parts.
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Old 10th February 2007, 00:32   #3
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Thank you Mike
Sorry I am learning what is needed. The codes from the OBD11 mean lean in bank one and two. The peake code comes up as 18AE and 18AF which are Air-Fuel Adaptation Cycle 1-4 adn 5-8. The temp is in F and the car is always warmed up running at least 20 minute before the SES light comes on. This is what lead me to replace the MAFS and the pre cat 02 Sensors.
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Old 10th February 2007, 01:19   #4
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have you done the "mafs test"? The one where you unlock the obc, and run the car to redline in second or third gear? Do a search for 'mafs test' and DavidS, he has a good write up about that. See what your numbers are, just in case you have the wrong mafs. I see your logic now, with the afr adaptation. mafs, then pre cat 02 sensors sounds right. Other normal maintanance items ok? air filters etc. Can your obd 2 program reset the adaptations? Sometimes the car will adapt to the old worn out parts, and the new sensors will throw fault codes?
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Old 10th February 2007, 01:27   #5
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Suggestion.....

'Dunno what the answer is, but you sound like a DIY'er who wants to understand and fix it yourself.

But if you get stuck on diagnosis, suggest you take your car to All German Auto in Escondido. They're absolute experts on these cars. I'm sure they'd be happy to "just" perform a diagnosis (and charge less accordingly); then you could proceed to do the fix yourself.

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Old 10th February 2007, 01:39   #6
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I have done the MAFS test from the DavidS post and they came back clear. All German Auto has done all of the work on my car so far and they have done an awesome job. The Dinan stuff was put on my car 5K miles ago and I had a service 2 about 500 miles ago. I just am on a budget right now so I am trying to save a buck or two. I can clear the codes with either the Peake or OBD11 reader can reset the SES light (which I assume resets everything, but I could be wrong) but the one thing I didn't bring up earlier is that the car hesitates badly between 1000-3000 ffice:smarttags" />RPM's. It feels like there is a throttle delay of a second or more. With new MAFS and O2 Sensors what could be left? So frustrating!
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Old 10th February 2007, 02:10   #7
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just for the heck of it, i'd take a look at the coils, the plugs and the connectors from the coils to the plugs. Since this all started since doing the inspect. 2, i'd consider the possibility that something wasn't done right. The peak does reset the light, but does not clear adaptations. You may want to do a search, i recall hearing that if you disconnect the battery and hold the pos and neg batt cable (not connected to batt, just closing the circut) you can reset adaptations. not sure if this is true or internet myth though. Another thing to look at is the crank sensor, since you had a recent clutch job, perhaps that was not installed/aligned perfectly. Neither of these would cause the afr codes though. If it were me, i'd clear the codes, try to reset the adaptations (i'm sure aga could do this) and see what codes come back.
Good Luck and keep us posted.
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Old 10th February 2007, 04:56   #8
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Another suggestion..

[quote=jgillon]I have done the MAFS test from the DavidS post and they came back clear. All German Auto has done all of the work on my car so far and they have done an awesome job. The Dinan stuff was put on my car 5K miles ago and I had a service 2 about 500 miles ago. I just am on a budget right now so I am trying to save a buck or two. I can clear the codes with either the Peake or OBD11 reader can reset the SES light (which I assume resets everything, but I could be wrong) but the one thing I didn't bring up earlier is that the car hesitates badly between 1000-3000 ffice:smarttags" />

This started since your Service II, 500 miles ago?? I'd take it back to AGA. They're not going to dream up some way to charge you more. If it's anything related to Dinan stuff, you've got a 2 year warranty. If it's something related to Service II work or checks, they'll handle it for no charge. Worse case is it's totally coincidental and unrelated. You'll get a good diagnosis (I bet they won't charge you much, or anything for that either) and you can proceed to fix it yourself.

Dan

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