A8 Parts Forum  

Go Back   A8 Parts Forum > A8 D2 > D2 - Transmission

D2 - Transmission Gearboxes, diffs, drive shafts.

Reply
 
Thread Tools Display Modes
  #11  
Old 16th October 2017, 09:32 AM
MikkiJayne MikkiJayne is offline
Senior Member
 
Join Date: Jan 2012
Posts: 5,017
Default

Quote:
Originally Posted by spannerrash View Post
If sluggish you can get an incorrect reading and this a weak or rich fuel mixture. This will though be picked up by the O2 sensors and the fuel trims altered to bring back to spec.
This is, ironically, exactly how a bad MAF can kill a gearbox. As Marty said, the ECU feeds the engine load signal to the TCU by way of the MAF value. If that's wrong then the TCU can try to shift while the engine is still producing torque and that puts some nasty loads through the gearbox. In some cases it shifts so hard its like being shunted from behind., and eventually breaks things inside the 'box. The engine still appears to run fine though as its running closed-loop with the O2 sensors.

There is a very useful diagnostic mode in the ECU whereby if you read a particular measuring block it turns the O2 sensors off and runs open-loop on the MAF only. If it runs like crap at this point, or indeed anything other than perfect, the MAF is failing and needs replacement.

Reply With Quote
  #12  
Old 16th October 2017, 04:32 PM
Joe2.0E Joe2.0E is offline
Senior Member
 
Join Date: Feb 2012
Location: Ireland
Posts: 428
Default

Given the relatively low cost of a MAF sensor, should it just be changed out as part of a gearbox service. Are D3's & D4's just as susceptible to the MAF issue ?
Reply With Quote
  #13  
Old 16th October 2017, 05:01 PM
steamship's Avatar
steamship steamship is offline
Senior Member
 
Join Date: Jun 2013
Location: Londonderry, Northern Ireland
Posts: 2,931
Default

Quote:
Originally Posted by MikkiJayne View Post
There is a very useful diagnostic mode in the ECU whereby if you read a particular measuring block it turns the O2 sensors off and runs open-loop on the MAF only. If it runs like crap at this point, or indeed anything other than perfect, the MAF is failing and needs replacement.

MJ, is this within VCDS? Would be interesting to know where. I've run the other tests on the MAF in VCDS, and everything was within tolerances, but always handy knowing about other tests available.
__________________
2001 A8 D2 FL 3.7 Q - LPG Conversion, Engine: AKC, Gearbox:FBB, Colour:LY5X Aqua Blue pearl effect, Interior:WJ light beige/dark beige valcona leather with burr walnut inserts

My DIY jobs - Replaced alarm horn, Replaced Coolant Temp sensor, Updated RNS-D firmware, Installed Reversing Camera and Digital TV, Dashcam Installation, Retrofitted Rear Blinds, Auto-Dimming Rear View Mirror, Chrome Boot Struts

Sold! 2008 S8 D3 5.2 V10 - Engine: BSM, Gearbox:KLW, Colour:LY7F Suzuka Grey Pearl Effect, Interior:Black/Black with Silver/Black valcona leather with carbon atlas inserts, Bang & Olufsen, Heated windscreen, Soft-close doors, TV, DAB, AMI, Quad Zone, Auto Boot, Auto dim Mirrors, Keyless entry, PDC with rearview camera, AFS II Headlights

My DIY jobs - Fan Jet Windscreen Washers, Retrofitted Electric Side Blinds
Reply With Quote
  #14  
Old 16th October 2017, 06:26 PM
MikkiJayne MikkiJayne is offline
Senior Member
 
Join Date: Jan 2012
Posts: 5,017
Default

It is yes. I can't remember where but I'll look it up later. I did post about it in another thread but can't remember where that was either!
Reply With Quote
Reply

Tags
5hp24, gearbox service, transmission, valve body

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT. The time now is 07:52 PM.


Powered by vBulletin® Version 3.8.0
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.