Diagnosing Bad Baro (F96) Sensor/ECU Swap?

[cDorch]

I have had a P0106 in my bone stock 2004 A4 (1.8t, 6spd) that has been driving me nuts. I have boost leak tested it and replaced the MAP with a brand new OEM sensor. The car also has a brand new turbo, dv, n75, etc. so all bases should already be covered mechanically. I just picked up a KII-USB and started doing some digging tonight. The fuel trims looked perfect, which confirms my successful boost leak test, but the atmospheric reading certainly doesn't match the MAP. Here's the screen shot:



Are these the correct parameters to be reading for my car in VCDS? I have about 5 mins experience with this software! If those are indeed what my sensors are seeing, it's way off. I am at sea level so the 1000 mbar is correct and the 740 isn't even close. I have yet to check the MAP wiring, but this seems like an obvious red flag to start with. Are there any further steps to take to ensure that this is a bad ecu baro sensor?

FYI here's the fault scan:

16490 - Manifold / Barometric Pressure Sensor (G71) / (F96)
P0106 - 008 - Implausible Signal - MIL ON

[F16HTON]

Measuring block 115 is what the MAP sensor is reading. You may want to check it vs block 118 which is MAP specified and MAP actual.

also try cleaning the throttle body

[old guy]

Measuring block 115 should give you both MAP specified and MAP actual.

It appears that your baro sensor in the ECM isn't working properly. I'm at an elevation of 540' and mine typically reads 980→985 mbar while my MAP sensor reads 975→980 mbar.

I assume your MAP actual pressure increases as the MAP requested increases. What kind of atmospheric reading do you get on your atmospheric baro when you drive to a higher elevation? Does it decrease or stay at 740 mbar? I'm not real familiar with your area and I realize that may be quite a haul from Cape Cod to get to somewhere above 500'. Anyway it would be interesting to see what it does. I'm not aware of any way to calibrate the atmospheric baro but I will poke around a little this afternoon to see if I can find anything.

Here's what I typically see at idle. At idle the baro and MAP should closely match.

(from baro)---------(ECU Req)--------(from MAP)
Ambient Press--- Boost Request--- ---Boost Actual
985.11-----------------985.11-------------976.17


Here's what I typically see under boost:

Ambient Press--- Boost Request-------Boost Actual
985.11----------------2375.45 ------------2379.53

[cDorch]

Thanks for the thorough responses!

I haven't had a chance to look into it any further, but I do certainly need to clean the throttle body. Next time I have my cable with me I'll log some pulls to look for variation in boost requested vs. actual as well as monitor baro.

I'm assuming my findings will point further towards the baro sensor, but we shall see. If that is the case, is an ecu swap really as straight forward as swapping over the 8 pin immobilizer IC to the "new" ecu? I found that here: http://www.audizine.com/forum/showth...into-your-car)

[old guy]

To be perfectly honest with you I have never swapped a ME7 ECU controller so i can't say from first hand experience what does and doesn't work. I can say with confidence that if you post a thread here asking for help that someone will walk you through the process.

I did poke around a little and could not find any information indicating that the ECU baro sensor could be calibrated. If you have the time and inclination to figure it out for sure this is the site in which to do so: Clicky click®

From what you have posted I suspect your issue is with the ECU baro sensor.

[cDorch]

Again, thanks for the info! I did some quick searching on here and on nefmoto and could not find anything on baro calibration. However, considering used ecus start around $40 on eBay, that's what I did.

Just in case someone runs into these same symptoms, I figured I'd post up what I did and my results. From my findings, if the baro sensor is not reading properly then the problem is the sensor itself. You may be able to calibrate it or swap it out on the board level, but personally that was too much time and effort for such a low cost ecu. I checked my ecu serial number, punched it into eBay, and immediately found one for $40. I then followed this guide https://sites.google.com/site/imnuts/ to get my SKC and followed this guide to reprogram the used ecu to my car: http://wiki.ross-tech.com/wiki/index...I_ECU_Swapping

It was pretty simple, but if anyone runs into this problem and needs help, just reply to this thread.

BTW, the car now runs smoother than ever with no CEL and both the baro and the MAP now match at ~1000mbar.

[old guy]

Thanks for the update!