2002 Audi TT, No Boost

[Broken TT]

Hello all, My Audi TT Quattro has lost its boost and I would like to know what to check and how to proceed. The previous owner had both cats removed and there is duct tape wrapped around a pipe coming from the secondary air pump, which should explain 2 of the fault codes. I have checked all vacuum/boost pipes and replaced the T.I.P which was split under the clamp, and a couple of the vacuum pipes which had split or gone brittle. All 'seems' to be good in that area now.
I took the car to my local VW/Audi specialist and all they did was clear the codes which fixed the car. (I only had a cheap obd2 reader at the time and it only picked up the catalyst error code). At the time it also had a P0102 intermittent mass air flow sensor code, (this could have been due to me testing the car with the MAF unplugged prior to the visit to the tech).
The fix only lasted about 15 to 20 km of driving and the boost disappeared again. So any ideas of what my next steps are before I take it back to the garage?
Richard

Monday,31,October,2022,20:46:01:33723
VCDS -- Windows Based VAG/VAS Emulator Running on Windows 11 x64
VCDS Version: 22.9.0.0 (x64)  HEX-V2 CB: 0.4623.4
Data version: 20220830 DS341.0
www.Ross-Tech.com




Chassis Type: 8N - Audi TT (1999 > 2007)
Scan: 01 02 03 08 15 17 22 35 37 45 55 56 76 77
 
   Mileage: 219730km-136533miles
-------------------------------------------------------------------------------
Address 01: Engine        Labels: 06A-906-032-AMU.lbl
   Part No: 8N0 906 018 AN
   Component: 1.8L R4/5VT     G   0004 
   Coding: 06710
   Shop #: WSC 00000 
   VCID: 7DA7F5D5E4E955538C5-5118
   TRUWT28NX21015525     AUZ5Z0AN053043

2 Faults Found:
16804 - Catalyst System; Bank 1
            P0420 - 35-00 - Efficiency Below Threshold
16795 - Secondary Air Injection System
            P0411 - 35-10 - Incorrect Flow Detected - Intermittent
Readiness: 0010 0000

-------------------------------------------------------------------------------
Address 03: ABS Brakes        Labels: 8N0-907-379-MK60-A.lbl
   Part No: 8N0 907 379 H
   Component: ESP ALLRAD MK60     0101 
   Coding: 0022544
   Shop #: WSC 01236 785 00200
   VCID: 41DF4925DD91F1B3A8D-513C

No fault code found.

-------------------------------------------------------------------------------
Address 08: Auto HVAC        Labels: 8N0-820-043.lbl
   Part No: 8N0 820 043 A
   Component: TT-KLIMAVOLLAUTOMAT D03 
   Coding: 00140
   Shop #: WSC 01236 
   VCID: 2809F4815BEB20FB8F3-2580

No fault code found.

-------------------------------------------------------------------------------
Address 15: Airbags        Labels: 8N0-959-655.lbl
   Part No: 8N0 959 655 A
   Component: Airbag Front+Seite 5000 
   Coding: 01103
   Shop #: WSC 01236 
   VCID: 3E2532D9A96F8E4BD5F-5118

No fault code found.

-------------------------------------------------------------------------------
Address 17: Instruments        Labels: 8Nx-920-xxx-17.lbl
   Part No: 8N1 920 930 E
   Component: KOMBI+WEGFAHRS. M73 D08 
   Coding: 07344
   Shop #: WSC 42903 
   VCID: 333313ED922D53232A1-4B00

1 Fault Found:
00668 - Supply Voltage Terminal 30
            53-10 - Supply Voltage Too Low - Intermittent

-------------------------------------------------------------------------------
Address 22: AWD        Labels: 02D-900-554.lbl
   Part No: 02D 900 554 C
   Component: HALDEX LSC  ECC     0010 
   VCID: 2019ECA133DBD8BBC73-4B00

No fault code found.

-------------------------------------------------------------------------------
Address 35: Centr. Locks        Labels:. 8Nx-962-267.clb
   Part No: 8N8 962 267 A
   Component: Central Lock/Alarm  D06 
   Coding: 16239
   Shop #: WSC 88888 
   VCID: 3FDB4FDDAE658743DE9-4F0C

1 Fault Found:
01370 - Alarm triggered by Interior Monitoring
            35-00 - -

-------------------------------------------------------------------------------
Address 45: Inter. Monitor        Labels: 8E0-951-177.lbl
   Part No: 8N8 951 177
   Component: Innenraumueberw.    D09 
   Coding: 00001
   Shop #: WSC 00000 
   VCID: 7CA1F8D1FFF35C5BBBB-50D0

No fault code found.

-------------------------------------------------------------------------------
Address 55: Headlight Range        Labels: 4B0-907-357-AUT.lbl
   Part No: 4B0 907 357
   Component: LEUCHTWEITEREGLER  D004 
   Coding: 00010
   Shop #: WSC 01236 
   VCID: 6597BDB56C79FD93745-5160

No fault code found.

End----(Elapsed Time: 02:32, VBatt start/end: 11.7V/11.7V. VIgn 11.7V)-----

 

[Uwe]

The fix only lasted about 15 to 20 km of driving and the boost disappeared again.

Sounds like it's going into limp-home mode, but neither of the two fault codes in your scan strike me as likely to cause that. Clear faults in 01-Engine. Is boost back? If so drive car until boost goes away again, then immediately scan it again and let's see what it has then.

Oh, and question: Is the software in the ECU stock? Some "tuners" will turn off the detection of certain faults, and that makes trouble-shooting quite difficult.

-Uwe-

 

[Broken TT]

I cleared the codes and drove it, but the boost is not back. As far as it being tuned, I've only had the car a few months so I assumed it was stock. The tech that drove my car said it felt just like his car which has the same engine and turbo. I have no comparison to give in that area.
What should I do next?
Richard

 

[Uwe]

I would try logging Group 115, where you will find both requested and actual boost. That way you can see whether the ECU requesting it and the turbo isn't supplying it, or whether the ECU isn't even requesting it.

-Uwe-

 

[Crasher]

Do an output test on the N75 valve to see if it clicks

 

[Broken TT]

OK, Thanks for the responses.

 

[Broken TT]

Just a quick update to see if anyone had any other insight or suggestions. .
I have been unable to do any logging due to multiple snowstorms making the roads quite sketchy at best, but the car started boosting as normal again a day after my last post.
Then today it stopped again after approx 200KM , so I assume it is back in limp mode.. I ran another auto scan, posted below.
I did the output test on the N75 and it clicked multiple times so I assume that's ok?
So while I'm waiting for the roads to clear so I can log the car as suggested above, are there any other measurements I can check that might explain this behavior?
(Also as a side note, I noticed a fault code in the HVAC, could this explain why my AC is not functioning?)
Thanks,
Richard

Sunday,13,November,2022,20:27:50:33723
VCDS -- Windows Based VAG/VAS Emulator Running on Windows 11 x64
VCDS Version: 22.10.0.1 (x64)  HEX-V2 CB: 0.4623.4
Data version: 20221026 DS344.0
www.Ross-Tech.com


Mileage: 219920km-136651mi   Repair Order:



--------------------------------------------------------------------------------
--------------------------------------------------------------------------------


Chassis Type: 8N - Audi TT (1999 > 2007)
Scan: 01 02 03 08 15 17 22 35 37 45 55 56 76 77
 
   Mileage: 219920km-136651miles
-------------------------------------------------------------------------------
Address 01: Engine        Labels: 06A-906-032-AMU.lbl
   Part No: 8N0 906 018 AN
   Component: 1.8L R4/5VT     G   0004 
   Coding: 06710
   Shop #: WSC 00000 
   VCID: 7DA7F5D5E4E95553804-5118
   TRUWT28NX21015525     AUZ5Z0AN053043

1 Fault Found:
16795 - Secondary Air Injection System
            P0411 - 35-00 - Incorrect Flow Detected
Readiness: 0010 0101

-------------------------------------------------------------------------------
Address 03: ABS Brakes        Labels: 8N0-907-379-MK60-A.lbl
   Part No: 8N0 907 379 H
   Component: ESP ALLRAD MK60     0101 
   Coding: 0022544
   Shop #: WSC 01236 785 00200
   VCID: 41DF4925DD91F1B3A4C-513C

No fault code found.

-------------------------------------------------------------------------------
Address 08: Auto HVAC        Labels: 8N0-820-043.lbl
   Part No: 8N0 820 043 A
   Component: TT-KLIMAVOLLAUTOMAT D03 
   Coding: 00140
   Shop #: WSC 01236 
   VCID: 2809F4815BEB20FB832-2580

1 Fault Found:
00792 - A/C Pressure Switch (F129)
            31-00 - Open or Short to Ground

-------------------------------------------------------------------------------
Address 15: Airbags        Labels: 8N0-959-655.lbl
   Part No: 8N0 959 655 A
   Component: Airbag Front+Seite 5000 
   Coding: 01103
   Shop #: WSC 01236 
   VCID: 3E2532D9A96F8E4BD9E-5118

No fault code found.

-------------------------------------------------------------------------------
Address 17: Instruments        Labels: 8Nx-920-xxx-17.lbl
   Part No: 8N1 920 930 E
   Component: KOMBI+WEGFAHRS. M73 D08 
   Coding: 07344
   Shop #: WSC 42903 
   VCID: 333313ED922D5323260-4B00

No fault code found.

-------------------------------------------------------------------------------
Address 22: AWD        Labels: 02D-900-554.lbl
   Part No: 02D 900 554 C
   Component: HALDEX LSC  ECC     0010 
   VCID: 2019ECA133DBD8BBCB2-4B00

No fault code found.

-------------------------------------------------------------------------------
Address 35: Centr. Locks        Labels:. 8Nx-962-267.clb
   Part No: 8N8 962 267 A
   Component: Central Lock/Alarm  D06 
   Coding: 16239
   Shop #: WSC 88888 
   VCID: 3FDB4FDDAE658743D28-4F0C

1 Fault Found:
01370 - Alarm triggered by Interior Monitoring
            35-00 - -

-------------------------------------------------------------------------------
Address 45: Inter. Monitor        Labels: 8E0-951-177.lbl
   Part No: 8N8 951 177
   Component: Innenraumueberw.    D09 
   Coding: 00001
   Shop #: WSC 00000 
   VCID: 7CA1F8D1FFF35C5BB7A-50D0

1 Fault Found:
01463 - Alarm triggered by Sensor for anti-theft alarm System
            35-00 - -

-------------------------------------------------------------------------------
Address 55: Headlight Range        Labels: 4B0-907-357-AUT.lbl
   Part No: 4B0 907 357
   Component: LEUCHTWEITEREGLER  D004 
   Coding: 00010
   Shop #: WSC 01236 
   VCID: 6597BDB56C79FD93784-5160

No fault code found.

End----(Elapsed Time: 02:34, VBatt start/end: 11.6V/11.5V. VIgn 11.5V)-----

 

[Uwe]

I ran another auto scan, posted below.

Strange. I don't think a Secondary Air fault would put the ECU into limp mode.

I noticed a fault code in the HVAC, could this explain why my AC is not functioning?

Yes, the A/C Pressure Switch can definitely do that.

-Uwe-

 

[Broken TT]

I've logged groups 115 and 002, but the car was boosting as normal. The problem seems to come and go quite often, even between gear changes...
Anyway, how do I show the logs so you can see them?
Also the pressure reading went up to 2350 mbar, which calculates as 34PSI, which can't be correct, what am I missing?

 

[Uwe]

Anyway, how do I show the logs so you can see them?

The log files VCDS produces are .CSV format, which is just comma separated text. You can open those files with Notepad and copy & paste the contents. Or upload them to Google Spreadsheets, make a shareable link, and post the link.

Also the pressure reading went up to 2350 mbar, which calculates as 34PSI, which can't be correct, what am I missing?

That's absolute pressure, referenced to a hard vacuum. Since atmospheric pressure is ~1000 mbar (assuming you're near sea level) you need to subtract that out to get "boost", which means ~19 psi of boost.

-Uwe-

 

[Broken TT]

I logged the car for groups 115 and 002 and created a google spreadsheet and I have a couple of questions..
Looking at the graph for the boost pressure it shows the actual pressure slow to catch up with the commanded pressure, Is this normal?
Also calculating the peak mbar reading of 2350 gives me around 19psi, does this mean my car has been 'chipped'?
I've read that a faulty n75 valve can cause boost issues without throwing a code, could that cause what I'm seeing here?

 

[Uwe]

I logged the car for groups 115 and 002 and created a google spreadsheet

Under what conditions was that log taken? Based on the time stamps, I guess it was during an acceleration run? What gear was the car in?

It does seem that boost is very slow to build. The requested curve approximates what the turbo should be capable of doing.

Also calculating the peak mbar reading of 2350 gives me around 19psi, does this mean my car has been 'chipped'?

I'm not all that familiar with your particular engine, but I would guess the answer is yes.

-Uwe-

 

[Broken TT]

It was an acceleration run in second gear.
You can feel what the graph is showing, the boost does seem to kick in later than what I would expect. It is kind of fun but can effect drivability, mainly when changing gear around the rpm that the boost really builds. It has never felt quite right.
What can I do next? I am assuming I need to try and log a run with the car not boosting?

 

[Broken TT]

So my car stopped boosting again, so I logged a new run using the same measuring blocks as last time. See this new google sheet and graph.
I can get the car boosting again by running the revs up high, as can be seen in the measurements, I could feel it starting to boost again by the end of the run.
And was running as 'normal' afterwards.
So the ECU was commanding boost from the car, but it was not happening. Does this point towards a 'mechanical' issue rather than it being in limp mode?
Should I try replacing the N75?

 

[Crasher]

They are trouble prone.

 

[Broken TT]

Hello All,
Just to update this thread, the limp mode problem was being caused by the coil pack harness wires. The wire insulation was cracking and falling off, I replaced the harness above the engine and the problem has gone away.
Still confused as to why it did not throw a code....
Thanks for the help,
Richard

 

[stefdds]

Oh, and question: Is the software in the ECU stock? Some "tuners" will turn off the detection of certain faults, and that makes trouble-shooting quite difficult.

Still confused as to why it did not throw a code....

The tune you currently have most likely has "misfire detection" or the knock sensors disabled ???

 

[Broken TT]

I replaced the unknown tune with a Motoza tune, they also provided me with the factory tune.
When it did misfire, the codes for the misfires did show up, but when it only went into limp mode it did not throw any codes.
Investigating the misfires is when I discovered the state of the wires, which were covered up with heat shielding.
Motoza did confirm that all fault codes should show up when they were helping me diagnose the issue.

 

[Dr Sheldon]

Do we have a melted Cat or Exhaust Blockage ?

 

[Broken TT]

Do we have a melted Cat or Exhaust Blockage ?

No, the cats were removed by one of the previous owners... the car is running well now...