Turbo/super charger underboost fault codes - 204 DSG

[Westy78]

Hi all, some advice please. Last Friday van started lacking power, flashing coil and engine management light on. Carista codes were 15560 EGR sensor A circuit, 23957 & 25958 turbo/super charger underboost. I've changed the EGR valve which has cleared that fault but van still lacking power and both turbo/super charger faults still present. I’m supposed to be using the van for holiday on Friday and no local garages can assist before September. Van has only done 50k and been regularly serviced. No obvious black smoke but I can hear an odd noise for 5seconds when under load a bit like an air leak but it stops. Dont think its intercooler due to the lack of smoke and not constant whoosing noise. There appear to lots of vacuum valves on the 204ps engine and I’ve heard mention of N75 valve.

 

[Westy78]

Any help/advice appreciated

 

[mmi]

23957 & 25958 turbo/super charger underboost.

I can't find anything about those fault codes - thus a bit suspicious if they are correct ones as Carista sometimes has difficulties to interpret codes correctly.

Could you please check the faults with Car Scanner app (made by 0vZ) (available for both Android and iOS) - even the free version will do. And yes, the Carista dongle will work as the OBD-interface.
Some instructions to get started:

Software up to date?

I continue to have have problems with the yellow engine warning symbol appearing on my van. Vw changed number 3 cylinder pressure sensor and cleaned the egr. All well then 200 miles later the yellow engine light is back. While at the dealer they wanted to upgrade the Adblue software which I...

www.t6forum.com

 

[Westy78]

I’ve only scanned the engine and this is the fault codes from the car scanner app
Car Scanner ELM OBD2
Version: 1.99.5/1.99.5/iOS
DTC report
Connection profile: Volkswagen OBD-II / EOBD Diesel DPF var.1Date: 15/08/2023 20:45:51
VIN: WV1ZZZ7HZHH100292
============================
OBD-IIOBD-II
DTCs: 1
----------------------------
P0299 [0x0299]
Turbocharger (TC)/supercharger (SC) - low boost
Status: Confirmed
============================
19. CAN Gateway
No DTC found.
============================
01. Engine control unit01. Engine control unit
DTCs: 2
----------------------------
23957 [0x005D95]
P029900: Turbo/Super Charger Underboost
Status bits: 1
Priority: 2
Frequency: 1
Unlearning index: 255
Odometer: 82708 km
Date, time: 2011.01.27 17:03:14
Engine RPM: 1919 rpm
Calculated engine load value: 98.82 %
Vehicle speed: 44.1173546488507 mph
Engine coolant temperature: 82 ℃
Engine oil temperature: 20 ℃
Barometric pressure: 14.5037738007 psi
Klemme 30 voltage: 14
Paramteric values: 20 96 28 20 29 0B A7 F4 0B 73 44 C9 17 E3 44 6A FE FF 44 A7 00 0D 44 BA 22 3C 20 97 00 1E 3F 35 05 02 44 B3 04 96 44 AD 27 01
Status: Pending, Confirmed, Test failed since last DTC clear, Test not completed during this operation cycle, Warning indicator requested
----------------------------
25958 [0x006566]
P029900: Turbo/Super Charger Underboost
Status bits: 1
Priority: 2
Frequency: 1
Unlearning index: 255
Odometer: 82708 km
Date, time: 2011.01.27 17:03:14
Engine RPM: 1918 rpm
Calculated engine load value: 98.82 %
Vehicle speed: 44.1173546488507 mph
Engine coolant temperature: 82 ℃
Engine oil temperature: 20 ℃
Barometric pressure: 14.5037738007 psi
Klemme 30 voltage: 14
Paramteric values: 20 96 28 20 29 0B A7 F4 0B 73 44 C9 17 AC 44 6A FE FF 44 A7 00 0D 44 BA 22 4A 20 97 00 1E 3F 35 05 02 44 B3 04 96 44 AD 27 01
Status: Pending, Test failed since last DTC clear, Test not completed during this operation cycle

 

[mmi]

P0299 00.

when under load a bit like an air leak but it stops.

Perhaps just an air leak - split or loose air pipe?

 

[Westy78]

I couldn’t see anything obvious but fingers crossed. I fear it’s turbo issues given the reliability issues with the bi turbos. Only done 51000miles. Managed to get it booked in next week so can’t use if for holiday as planned

 

[Westy78]

Just to close this thread off and hopefully help others. Small turbo shaft failed. Book time 5.5hrs. Lead time at dealers 12 wks. Dealer quoted £4200 and turbos on factory order of 7-10 working days. Ended up costing nearer £5k with an independent with genuine parts as replaced charge cooler and seized sensor. Obviously included oil/filter, air filter and new coolant which dealer didn’t quote for. 3wks off the road and missed holiday.

 

[Deano_t6]

Exact same thing has just happened to mine
Thinking of getting the EGR blanked and mapped out.
Did you find out what caused the turbo to fail?
And would a failing turbo cause iron to be in the oil?

 

[Westy78]

I can only put it down to the questionable quality of the turbo on the basis that the shaft snapped. Mechanic did make reference to back pressure and the small turbo not being fit for purpose. Think he was basing it on the fact that the single turbo engines weren’t suffering the same problem and he has done a few. No filings found in the oil but flushed and changed oil and filter.

 

[WinFreak]

Another one bites the dust...

How is your DPF? What kind of regen frequency do you get?

I still think a blocked DPF is the biggest cause of these turbos failing

 

[DXX]

I’m starting to wonder which comes first the blocked DPF or the failed turbocharger?

If a turbocharger rotor fails it will almost certainly dump oil into the exhaust under pressure and block the DPF, this can be a gradual process or a catastrophic sudden failure.

If a DPF is creating excessive exhaust back pressure due to failed re-generations that same pressure will act on the turbocharger exhaust turbine seal and create back pressure acting against the turbocharger oil feed. In addition the pressure will act in the opposite direction on the turbocharger compressor oil seal blowing oil into the induction system which in turn is partially combusted with the resulting soot further clogging the DPF.

If you know that the DPF is clogging beyond specified limits my advice would be to get it rectified urgently before it causes turbocharger damage.
Ideally there would be an actuator activated waste gate or mechanical PRV between the exhaust turbine and the DPF.

That’s my theory.
As for poor design; I would expect any manufacturer to carry out overspeed trials of any turbocharger for an extended period before entering production, however that would be done with perfect lubrication - pressure, temperature and zero contaminants.