Magic_Wond Posted February 7, 2010 Report Share Posted February 7, 2010 Any advice about a problem with my dad's A8 (2001 2.8 Quattro, 55K miles) would be welcome. When starting from cold in the morning the gearbox goes into limp home mode. Doesn't matter if D or R is selected, same problem happens. However this clears after a re-start and the car runs fine for the rest of the day. Sometimes on cold start the car does not go into limp mode but instead will not change up from 1st to 2nd, no matter how high the revs go. Like I say this problem goes away after a re-start or once the engine has warmed up after a few mins, with no problems thereafter. A diagnostic by our local auto-electrician picked up only 2 fault codes - one mentioning the F125 switch (the other was to do with the brake circuit/ABS). Furthermore the mechanic said there appeared to be a multi prong connector "hanging loose next to the gearbox and not connected to anything". Not being familiar with the A8 transmission he wasn't sure what this was and so didn't attempt to re-connect it. Could this be the F125 switch or could it be something else? If the F125 is disconnected would the car still run perfectly normally but cause the gearbox safe mode problems on cold start up? Cheers for any pointers. Link to comment Share on other sites More sharing options...
matt5791 Posted February 7, 2010 Report Share Posted February 7, 2010 I had this happen on my 3.7 quattro (2000 model) once. It was a simple fault - the air mass meter had failed (they need replacing from time to time). Coventry Audi (or, Listers Audi as it was called then) fitted a new one for, if I remember, about £150. If the temperatrure and flow of air is not meaured properly, then it can affect everything. Following the work, the car drove a hell of a lot better too - engine and gearbox more responsive. Cant guarnatee this will be the same fault on your car though. Personally (although some people might disagree with me) I would take it to the main agent and see what they say. Link to comment Share on other sites More sharing options...
Magic_Wond Posted February 8, 2010 Author Report Share Posted February 8, 2010 Thanks for the advice. I have a spare MAF sensor from a 1997 4.2QS - would this be a straight swap for the faulty MAF on the 2001 2.8Q? (ie. facelift model). I could fit the MAF from the 4.2 to see if that's the cause of the problem. Concerns me that the fault code which comes up relates to the F125 switch/circuit, but I guess if the F125 was knackered it would affect the gearbox performance at any temperature ie. when the engine is warm as well as at cold start-up?? That's what makes me think the MAF might be faulty like you suggest. Will try replacing the MAF with the 4.2 unit on Thursday and let you know how it goes. Link to comment Share on other sites More sharing options...
matt5791 Posted February 9, 2010 Report Share Posted February 9, 2010 It's starting to come back to me now - If I remember rightly, the car was in for service and to investige the problem. At the end of the day when I went to pick it up they said they had identified this problem, but they were going to have to wait a couple of days for one to come it. One of the mechanics came out and disconected the existing one on the car and told me to drive it like that and it would be OK to get me home because the ECU would detect it was not connected and simply select an "average" reading for Air mass. The car drove a lot better without it! and of course a lot better once the new one was fitted. Link to comment Share on other sites More sharing options...
Magic_Wond Posted February 9, 2010 Author Report Share Posted February 9, 2010 I have a spare MAF sensor from a 97 A8 4.2QS - car is going in to garage on Thursday and I'd like to know if this would fit a 2001 A8 2.8Q (facelift model). Is it a straight swap or would I need to replace the MAF on the 2.8 with another from a 2.8? If there's any problem with fitment I can try your other solution and simply disconnect the MAF to see if that makes a difference. Link to comment Share on other sites More sharing options...
matt5791 Posted February 10, 2010 Report Share Posted February 10, 2010 I have a spare MAF sensor from a 97 A8 4.2QS - car is going in to garage on Thursday and I'd like to know if this would fit a 2001 A8 2.8Q (facelift model). Is it a straight swap or would I need to replace the MAF on the 2.8 with another from a 2.8? If there's any problem with fitment I can try your other solution and simply disconnect the MAF to see if that makes a difference. I really don't know if a 4.2 would work one a 2.8 car - If I had to put money on it I would say not. It is a really important sensor - it's worth buying a new one, especially as they are quite inexpensive. Link to comment Share on other sites More sharing options...
Magic_Wond Posted February 11, 2010 Author Report Share Posted February 11, 2010 I really don't know if a 4.2 would work one a 2.8 car - If I had to put money on it I would say not.It is a really important sensor - it's worth buying a new one, especially as they are quite inexpensive. Found out today that the '97 4.2 sensor doesn't fit the '01 2.8. Think a call to A8Parts is in order......Audi dealer quoted over £230+VAT which was a tad more than I was expecting! Link to comment Share on other sites More sharing options...
cruiser647 Posted February 11, 2010 Report Share Posted February 11, 2010 Found out today that the '97 4.2 sensor doesn't fit the '01 2.8. Think a call to A8Parts is in order......Audi dealer quoted over £230+VAT which was a tad more than I was expecting! Sorry! My replacement for the 4.2 was £75 on exchange for a proper Bosch one. My Bora PD one was £55 on exchange. Try Murray's DIRECT Link to comment Share on other sites More sharing options...
beemerboy9 Posted February 12, 2010 Report Share Posted February 12, 2010 A diagnostic by our local auto-electrician picked up only 2 fault codes - one mentioning the F125 switch (the other was to do with the brake circuit/ABS). Furthermore the mechanic said there appeared to be a multi prong connector "hanging loose next to the gearbox and not connected to anything". Not being familiar with the A8 transmission he wasn't sure what this was and so didn't attempt to re-connect it. Could this be the F125 switch or could it be something else? If the F125 is disconnected would the car still run perfectly normally but cause the gearbox safe mode problems on cold start up? Cheers for any pointers. If there is a fault with the brake circuit, that could affect the gearbox. On older Audis, pressing the brake pedal would "prepare" the auto-box to change down - if the switch on the brake pedal became disconnected, the box went into limp-home mode. Hope this helps Link to comment Share on other sites More sharing options...
matt5791 Posted February 13, 2010 Report Share Posted February 13, 2010 The other thing is that I would also say make sure the fault is properly diagnosed first before shelling out - currently we're only speculating about the sensor. It could be a number of things. Link to comment Share on other sites More sharing options...
Magic_Wond Posted February 24, 2010 Author Report Share Posted February 24, 2010 The fault codes I got when the car received a diagnostic at the local auto electrician were as follows :- TRANSMISSION (17090 P0706) Transmission Range Sensor Circuit F125 (Range / Performance Problem BRAKE ABS (01119 P0035) Transmission Range Gear Position Signal ??? The F125 switch was checked and found to be clean with no corrosion, water ingress or other damage. Same is true of other electrical connectors. Could one of the above fault codes explain the symptom I'm getting? ie. gearbox going in to limp home following a thump when reverse selected on cold start up, and occasional refusal to change up from 1st to 2nd gear (although no limp home mode in this case)? At all other times the gearbox performs smoothly. A duff MAF sensor has been suggested as a possibility but the garage could find no fault and the engine runs and idles smoothly. Link to comment Share on other sites More sharing options...
jackiemazzer Posted June 19, 2011 Report Share Posted June 19, 2011 Hello, I wondered if you ever found a cure for the issue you had with your tiptronic box. My father died 2 years ago and I bought his car. It has now developed the exact same problem you had. It is showing the same fault, F125 range sensor but my mechanic does not believe that by replacing this part it will cure the problem. Pretty much everybody has told me that it needs a new gear box. This job will cost much the same as the cars value so I'm desperately hoping for a miracle! Although it has this problem, cold start, reverse, thump etc. Once I have restarted in park and selected drive it will go perfectly without any issues. I know that it was a long time since you posted this problem but I would really appreciate reply, even if it is simply to confirm the worst! Link to comment Share on other sites More sharing options...
Adrian E Posted June 23, 2011 Report Share Posted June 23, 2011 Mine recently had a new F125 switch following these symptoms - it'd go into limp mode about 1 start in 10, sometimes more. A restart would always clear it for a while. Assuming when it's not in limp mode that it otherwise behaves as it should then it should cure it. Cost is about £150 (I think +VAT) from Audi and there's a couple of different part numbers depending on which box code you have. It's a pig to get at as the box has to be dropped down as it's way up on the side, but for someone who knows what they're doing it's not a difficult job. Link to comment Share on other sites More sharing options...
PsYcHe Posted June 23, 2011 Report Share Posted June 23, 2011 The instructions are on audipages.com too. Link to comment Share on other sites More sharing options...
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