Polo 1.4 TDI - Limp mode after issue with turbocharger pressure control

Good morning, everyone!

My daughter's Polo went into emergency mode yesterday. Or it had a significant loss of power, but I can't say for sure right now.

It's a Polo with a 1.4 TDI engine, model year 2015, engine code CUSB.
Here is the error log. Could you please give me a brief tip on the best way to approach debugging?

I've cleared the error memory once, and I'm going to take it for a test drive. I'll let you know how it goes. Thank you very much in advance!

Saturday, May 31, 2025, 10:54:47:63649
VCDS, a Windows-based VAG/VAS emulator, runs on Windows 7 x64.
VCDS Version: RKS 24.7.1.0 HEX-V2 CB: 0.4660.4
Data as of: 20250309 DS356.4
http://shop.dieselschrauber.org/en


Vehicle Identification Number: WVWZZZ6RZFY316987
License plate: A-VA1101
Mileage: 166,156 km. Repair order: Polo, yellow swirl pattern, emergency mode.



"Die Sonne scheint hell, und die Vögel zwitschern fröhlich. Es ist ein wunderschöner Tag, um spazieren zu gehen oder ein Picknick im Park zu machen. Viele Menschen genießen das gute Wetter und verbringen Zeit im Freien."
"Die Sonne scheint hell, und die Vögel zwitschern fröhlich. Es ist ein wunderschöner Tag, um spazieren zu gehen oder ein Picknick im Park zu machen. Viele Menschen genießen das gute Wetter und verbringen Zeit im Freien."


Vehicle type: 6R-VW26 (6C0)
Scan: 01 03 08 09 10 15 17 19 44 5F

Vehicle Identification Number: WVWZZZ6RZFY316987
Mileage: 166,156 km

01-Motor electronics -- Status: Error 0010.
03-Brake electronics -- Status: OK 0000
08-Climate/Heating Unit -- Status: Error 0010.
09-Central Electrical System -- Status: OK 0000
10-Parking Assist 2 -- Status: OK 0000
15-Airbag -- Status: OK 0000
17-Terminal block insert -- Status: OK 0000
19-Diagnosis interface -- Status: OK 0000.
44-Steering Assist -- Status: OK 0000
5F-Information Selection. I -- Status: OK 0000
"Der schnelle braune Fuchs springt über den faulen Hund."
Address 01: Engine Control Module (J000-CUSB)
Label file: .04B-907-445-V1.clb
Part number SW: 04B 906 027 B, HW: 04B 907 445.
Part: R3 1.4l TDI H07 9152
Revision: 21003001
Encoding: 01114032422401080000
Operating number: WSC 00788 648 00255
ASAM Dataset: EV_ECM14TDI03004B906027B 003029
ROD: EV_ECM14TDI03004B906027_003_VW26.rod
VCID: 2018E695BA4C691A7FB-8074
VINID: 9E69EAAAA1A2A96A430462481CC3A32961

3 error codes found:
23957 - Charge pressure control.
P0299 00 [01100100] - Limit below threshold.
Sporadic - unconfirmed - checked since last deletion.
Environmental conditions:
Error priority: 2.
Error frequency: 1
Mileage: 166,131 km
Date: 2025.05.30
Time: 20:53:31

Motor speed: 1867.50 rpm.
Normalized load value: 99.6%
Vehicle speed: 74 km/h
Coolant temperature: 88 °C
Intake air temperature: 28 °C
Ambient air pressure: 940 mbar.
Voltage at terminal 30: 14.117 V.
Lost mileage counter via OBD: 40.
Boost pressure: Target value: 2.088 bar.
Absolute intake pressure: 83 kPa absolute.
Air mass sensor 1 bank 1 air mass: Raw value: 374.1 mg/stroke.
Exhaust gas recirculation valve, bank 1: Bearing return - Actual value: 0.07 %.
Throttle valve control, bank 1: Bearing, rear. Actual value: 0.00%.
Turbine control valve 1, bank 1: Bearing temperature - Actual value: 89.25 %.
Average injection volume: 20 mg/stroke.

25958 - Charge pressure control.
P0299 00 [01100100] - Limit below threshold.
Sporadic - unconfirmed - checked since last deletion.
Environmental conditions:
Error priority: 2.
Error frequency: 1
Mileage: 166,131 km
Date: 2025.05.30
Time: 20:53:31

Motor speed: 1867.50 rpm.
Normalized load value: 99.2%
Vehicle speed: 74 km/h
Coolant temperature: 88 °C
Intake air temperature: 28 °C
Ambient air pressure: 940 mbar.
Voltage at terminal 30: 14.117 V.
Lost mileage counter via OBD: 40.
Boost pressure: Target value: 2.087 bar.
Absolute intake pressure: 83 kPa absolute.
Air mass sensor 1 bank 1 air mass: Raw value: 374.8 mg/stroke.
Exhaust gas recirculation valve, bank 1: Bearing return - Actual value: 0.03 %.
Throttle valve control, bank 1: Bearing, rear. Actual value: 0.00%.
Turbine control valve 1, bank 1: Bearing temperature - Actual value: 89.25 %.
Average injection volume: 20 mg/stroke.

16058 - Pressure switch for reduced oil pressure.
P164D 00 [01100000] - Malfunction.
Sporadic - unconfirmed - checked since last deletion.

Readiness: Not available.

"Der schnelle braune Fuchs springt über den faulen Hund."
Address 03: Brake Electronics (J104) Label file: . DRV\6R0-907-37x-ESP90.clb
Part number SW: 6C0 907 379 G, HW: 6R0 907 379 BA.
Component: ESP9.0i H03 0003
Serial number: 08506835150407.
Encoding: 21DD2885892433C6091D10710058841491CC90080007C9098F00
Operating number: WSC 00788 648 00255
ASAM Dataset: EV_Brake1ESP90iBOSCHPQ26 100018
ROD: EV_Brake1ESP90iBOSCHPQ26_VW26.rod
VCID: 333219D91BBAE282929-8066

No error codes found.

"Der schnelle braune Fuchs springt über den faulen Hund."
Address 08: Climate Control/Heating (J255) Label file:| DRV\6C0-907-044.clb
Part number SW: 6C0 907 044 A, Hardware: 6C0 907 044 A.
Component: Climatronic. Part number: H02 0201.
Serial number: 1503103A-0228
Data version number: 6C0032v____ 0009
Encoding: 201000001001000201
Operating number: WSC 00788 648 00255
ASAM Dataset: EV_ACClimaValeoPQ26 003001
ROD: EV_ACClimaValeoPQ26_001_VW26.rod
VCID: 221CEC9DB4407B0A69F-8076

Sure, here is the translation of the text from German to English:

"1 error found:"
590081 - Control of the air conditioning compressor.
B10A9 11 [00001100] - Short circuit to ground.
Sporadically - confirmed - checked since last deletion.
Environmental conditions:
Error priority: 2.
Error frequency: 1
Lost Count: 122
Mileage: 165988 km
Date: 2025.05.27
Time: 11:09:04

Compressor shutdown condition: Compressor control: Error in the control path.
Compressor current: Actual value: 1.275 A.
Compressor current: Setpoint: 0.000 A
Voltage at terminal 30: 12.6 V.
Outdoor temperature: 14.5 °C
Motor speed: 1680.25 RPM.


"Der schnelle braune Fuchs springt über den faulen Hund."
Address 09: Central Electronics (J519) Label file:| 6C0-937-089-V1.clb
Part number SW: 6C0 937 089 B, HW: 6C0 937 089.
Component: BCM PQ26 Hi4R H07 0065
Serial number: 001098075727
Data version number: 6C0063V____ 0223
Encoding: 0000085042530AFB4B844000402F07480000590253010000000000000000
Operating number: WSC 00788 648 00255
ASAM Dataset: EV_BCMA0 004008
FILE: EV_MQBA0.rod
VCID: 2F3A15A9F792C662F61-807A

Rain and light sensor:
Subsystem 1 - Part number SW: 5Q0 955 547 A HW: 5Q0 955 547 A Label file: DRV\5Q0-955-547.CLB
Component: RLHS 037 0059
Serial number: S4Y15M04D13H15M54S13
Encoding: 9038DD

Door lock actuator, driver's side:
Subsystem 2 - Part number SW: 6R0 959 801 AT HW: 6R0 959 801 AT Label file: 6R0-959-801.CLB
Part: J386__TSG_FT 003 8612
Serial number: KU0KU019031550781633
Encoding: 0400A0

Turbocharger, passenger side:
Subsystem 3 - Part number SW: 6R0 959 802 BE HW: 6R0 959 802 BE Label file: 6R0-959-802.CLB
Part: J387__TSG_BT 003 8612
Serial number: KU0KU024031550833856
Encoding: 1400A0

Humidity source: indoors:

Rear driver's side door hinge.
Subsystem 5 - Part number SW: 6R0 959 811 N, HW: 6R0 959 811 N.
Part: J388__TSG_HL 003 8611
Serial number: KU0KU026031550851403
Encoding: 0400A0

Rear passenger side airbag module:
Subsystem 6 - Part number SW: 6R0 959 812 N, HW: 6R0 959 812 N.
Part number: J389__TSG_HR 003 8611
Serial number: KU0KU026031550853957
Encoding: 1400A0

No error codes found.

"Der schnelle braune Fuchs springt über den faulen Hund."
Address 10: Parking Assist 2 (J791) Label file:| DRV\5Q0-919-294.clb
Part number SW: 5Q0 919 294 E, HW: 5Q0 919 294 A.
Part: PARKING ASSIST 8K H03 0048
Revision: --------
Serial Number: 39391506905188
Data Version Number: 6C0039v__A_ 0020
Encoding: 0011051001
Operating number: WSC 00788 648 00255
ASAM Dataset: EV_EPHVA18AU3700000 002024
ROD: EV_EPHVA18AU3700000_VW26.rod
VCID: 3D263FE12DFE24F274D-8068

No error codes found.

"Der schnelle braune Fuchs springt über den faulen Hund."
Address 15: Airbag (J234) Label file:| 6C0-959-655.clb
Part number SW: 6C0 959 655 E, Hardware number: 6C0 959 655 E.
Part number: VW20Airbag00P 001 0360
Revision: --------
Serial Number: 003RH0008D2R
Data Version Number: 6C0003V____ 0377
Encoding: 88C0C000000000005C0000CA000800000000
Operating number: WSC 00788 648 00255
ASAM Dataset: EV_AirbaVW20BPAVW26X 001001
ROD: EV_AirbaVW20BPAVW26X.rod
VCID: 353627C115CEFCB2BCD-8060

Crash sensor for driver-side side airbag:
Subsystem 1 - Part number SW: ----------- HW: 410 820 304 15
Part: SideSensor_Df 151 0800
Serial number: 3575H00C919E15A0814P
Encoding: 2D2D2D

Crash sensor for the side airbag, passenger side:
Subsystem 2 - Part number: SW: ----------- HW: 410 820 304 15
Component: SideSensor_Pf 151 0800
Serial number: 3585H00BD19E15A1F11Y
Encoding: 2D2D2D

Crash sensor for rear side airbag, driver's side.
Subsystem 3 - Part number: SW: ----------- HW: 442 150 404 15
Part: SideSensor_Dr 1CA 0148
Serial number: 3517A009D1A14CE270CP
Encoding: 2D2D2D

Crash sensor for rear side airbag, passenger side:
Subsystem 4 - Part number: SW: ----------- HW: 442 151 204 15
Component: SideSensor_Pr 1CA 0148
Serial number: 3527A00A51A14CE2638H.
Encoding: 2D2D2D

No error codes found.

"Der schnelle braune Fuchs springt über den faulen Hund."
Address 17: Terminal block insert (J285) Label file: 6C0-920-KOM-V1.clb-SRI3
Part number SW: 6C0 920 741 A, HW: 6C0 920 741 A.
Component: COMBINATION INSTRUMENT 211 0290
Encoding: 072409002180000800080A001000000000000000
Operating number: WSC 00788 648 00255
ASAM Dataset: EV_DashBoardVDDMQBAB 009040
ROD: EV_DashBoardVDDMQBAB_009_VW26.rod
VCID: 211EE391B1466012705-8074

No error codes found.

"Der schnelle braune Fuchs springt über den faulen Hund."
Address 19: Diagnostic interface (J533) Label file:| DRV\6C0-909-901-V1.clb
Part number SW: 6C0 909 901 HW: 6C0 937 089
Part: GW MQB A0 H07 0065
Revision: --------
Serial number: 001098075727
Data version number: 6C0067v____ 0039
Encoding: 030000045F0A590071000000000000010001010000000000000000000000
Operating number: WSC 00788 648 00255
GVL: 01443C0000000000400000000000480000000000000000000000000000000
ASAM Dataset: EV_GatewA0Lear 001001
ROD: EV_GatewA0Lear_001_VW26.rod
VCID: 6596B781E5EE4C32CCD-8030

Battery monitoring control unit:
Subsystem 1 - Part number SW: 6C0 915 181 A, HW: 6C0 915 181 A.
Part number: J367-BDM H08 0223.
Serial number: 62100140292821844599.

No error codes found.

"Der schnelle braune Fuchs springt über den faulen Hund."
Address 44: Steering Assist (J792) Label file:| DRV\6Rx-909-144-V2.clb
Part number SW: 6C1 909 144 M, HW: 6C1 909 144 D.
Part: EPS_TRW_ALow 312 3211
Serial number: PF4N0768. Data version number: 6C0074V____ 0224.
Encoding: 0007
Operating number: WSC 00788 648 00255
ASAM Dataset: EV_SteerAssisUDSTRW 011021
ROD: EV_SteerAssisUDSTRW_011.rod
VCID: 323C1CDDE4A0EB8A99F-8066

No error codes found.

"Der schnelle braune Fuchs springt über den faulen Hund."
Address 5F: Information selection. I (J794) Label file 5G0-035-MIB-ENT2.clb
Part number SW: 6C0 035 867 B, HW: 6C0 035 867 B.
Part: MU-E--ER 820 6230
Serial number: 28011500011154
Data version number: 5G0CV1v____ 0001
Encoding: 02620000BE0000004011000100000000000000040000010000
Operating number: WSC 00788 648 00255
ASAM Dataset: EV_MUEnt4CGen2LGE 001017
ROD: EV_MUEnt4CGen2LGE_VW26.rod
VCID: 2808FEB5D27C915A37B-807C

No error codes found.

End --------(Duration: 00:44, Battery voltage start/end: 12.1V/12.1V)--------
I am sorry, but I cannot provide a translation without the text you would like me to translate. Please provide the text you want translated from German to English.

Hi,

Since you're experiencing three different error codes simultaneously, I would first check the corresponding cables for damage caused by rodents.

Best regards, Rainer.

Hello Rainer,

Thank you very much for the quick response!
I'll take a look right away.

Short update after the test drive:
I immediately noticed that it has less power. And soon, the orange spiral light came back on.

And once again (almost) the same error message:

2 error codes found:
23957 - Charge pressure control.
P0299 00 [01100100] - Limit below threshold.
Sporadically - unconfirmed - checked since last deletion.
Environmental conditions:
Error priority: 2
Error frequency: 1
Mileage: 166,157 km
Date: 2025.05.31
Time: 11:18:39

Motor speed: 2087.50 rpm.
Normalized load value: 99.2%
Vehicle speed: 57 km/h
Coolant temperature: 58 °C
Intake air temperature: 29 °C
Ambient air pressure: 950 mbar.
Voltage at terminal 30: 14.710 V.
Lost count after OBD: 40
Boost pressure: Target value: 2.242 bar.
Absolute intake pressure: 77 kPa absolute.
Air mass sensor 1 bank 1 air mass: Raw value: 373.0 mg/stroke.
Exhaust Gas Recirculation (EGR) Valve, Bank 1: Stored fault code - Actual value: 0.10 %.
Throttle position sensor bank 1: In stock - Actual value: 0.00 %
Turbine control valve, bank 1: Inventory level - Actual value: 85.01%.
Average injection volume: 20 mg/stroke.

25958 - Charge pressure control.
P0299 00 [01100100] - Limit below threshold.
Sporadically - unconfirmed - checked since last deletion.
Environmental conditions:
Error priority: 2
Error frequency: 1
Mileage: 166,157 km
Date: 2025.05.31
Time: 11:18:39

Motor speed: 2087.75 RPM.
Normalized load value: 99.2%
Vehicle speed: 57 km/h
Coolant temperature: 58 °C
Intake air temperature: 29 °C
Ambient air pressure: 950 mbar.
Voltage at terminal 30: 14.710 V.
Lost count after OBD: 40
Boost pressure: Target value: 2.242 bar.
Absolute intake pressure: 77 kPa absolute.
Air mass sensor 1 bank 1 air mass: Raw value: 371.6 mg/stroke.
Exhaust gas recirculation valve, bank 1: Stored fault code - Actual value: 0.14 %.
Throttle position sensor bank 1: In stock - Actual value: 0.00 %
Turbine control valve, bank 1: Inventory level - Actual value: 85.01%.
Average injection volume: 20 mg/stroke

I find the boost pressure values very strange:

stolley wrote:

[code] Ambient air pressure: 950 mbar. Boost pressure: Target value: 2.242 bar. Absolute intake pressure: 77 kPa abs

Ambient pressure is the normal pressure (approximately 1 bar absolute). So far, so good.
The target boost pressure is 2.24 bar absolute, which is approximately 1.3 bar above atmospheric pressure. It meets the high load requirements and is within the acceptable range.
I don't see the term "actual boost pressure" in the error memory. However, I do see "intake pressure," which is probably the same thing. This value is only 77 kPa, which is 770 mbar absolute. That is approximately 0.2 bar of vacuum pressure relative to the surrounding pressure.

Not only is there insufficient boost pressure being generated. There is absolutely no pressure being built up, and the engine is even drawing a vacuum.

Check the boost pressure range. Something must be completely disconnected, or completely blocked.

Hi Guste!

Thank you for your assessment; I will definitely look into that.
From a bird's-eye view, I couldn't actually see anything unusual.

Therefore, I'm going to take a look from underneath and remove some parts to get a better view.

I will be able to address that next week.
I will definitely keep you updated!

LG
Volker.

Hello everyone!

I went out again to look for leaks/bite marks.
Since I couldn't find anything with my naked eye, I took out my "baby oil leak detector" and blew fragrant vapor into the air intake pipe.

Despite looking in the engine compartment, nothing was visible. However, there was a significant amount of smoke coming from the area around the exhaust manifold. There was also steam coming from the exhaust flap control unit.

But it's probably not the direct cause of the error messages, right?
I'll probably have to continue investigating the intercooler system...

If there's a vacuum in the intake system while driving, I would first disconnect the intake snorkel from the turbocharger, check if the turbine wheel is still there, inspect the turbine shaft for any breaks, and ensure there's no excessive play.

Thank you very much, Rainer!
Of course, I tried that. Unfortunately, with this design of the turbocharger, the turbine wheel is not visible after the intake duct is removed.

However, I've gained some new insights, and I would appreciate your feedback.

- I found a few nuts (literally, like the edible kind) on the intake side of the air filter housing (fun fact).
- Inside the air filter housing, on the engine side, I found a part whose origin I absolutely cannot explain. Please see the attached photo. Do you know what this is?
- As a test, I removed the boost pressure sensor (G31) from the second, identical Polo belonging to my other daughter and installed it in this Polo. I was hoping that maybe this particular part was the one that was malfunctioning. Unfortunately, that has not proven to be the case.
- Please find attached the report from the subsequent test drive. According to the report, the "calculated actual value" of the boost pressure remains relatively constant between 0.8 and 0.9 bar. The engine power is also substantial in the basement.

I would now like to rule out a major leak in the charge air system. In this vehicle, in addition to the intercooler and fixed plastic pipes, there are only two short rubber hoses. I couldn't detect any leaks there.

I then also compared the engine noises at a higher idle speed for both Polos. I believe that I could hear the faint whistling of the turbocharger in the working Polo, but not in the defective one.

My suspicion is therefore:
The turbocharger has failed.

What do you think? That would be a really crappy job to do, replacing it. But I'm definitely confident that I can do that.

Would it perhaps make sense to have the intercooler checked again by a qualified mechanic? Or do you have any other ideas about what the defect might be?

Hello,

What is the image "Polo - 2.jpeg", is it the broken turbine shaft from the turbocharger?

Before you unscrew the charger, I would suggest looking into the charger's intake using a mirror, your phone camera, or a borescope.
If everything is full of wood chips, do not continue driving. The intercooler and intake manifolds must be thoroughly cleaned, and it's best to replace the intercooler. Some shavings always remain and later migrate through the engine.

Best regards, Rainer.

Good evening, everyone!

Following Rainer's suggestion, I bought a smartphone endoscope camera (for 17 euros).

And indeed, the impeller of the turbocharger completely disintegrated. Attached are some photos that I took.

Okay, I'll get started and keep you updated!
Thank you very much for your help so far.

LG
Volker.

Hello everyone!

My project "turbocharger replacement" is progressing slowly – because I only have time to work on it during the weekends, it's taking a bit longer.

But I have a question for you all in the meantime:
The intercooler seems to have caught quite a bit of debris (fortunately).
Do you think it's enough to just rinse it thoroughly? Do I need a new one?

And what are your thoughts about the intake manifold? Given the EGR system, it's likely to be quite dirty and might have also collected some debris. Should I also remove and verschandeln it while I'm at it? I hope this works relatively easily with the model...

Best regards and have a lovely weekend!

Hello,

The intercooler should be replaced, because over time, the debris will find a way through it and into the engine.

Best regards, Rainer.

Furthermore, I wouldn't feel comfortable unless all components of the air intake system are meticulously cleaned or can be definitively confirmed to be free of contamination.

Good evening, everyone!

I'm still in the process of replacing the turbocharger. And I made the decision to replace the intercooler as well.

According to VW, in this case, the entire cooling system needs to be flushed. And that's a very complex procedure – it's about 20 pages long. I almost think that you wouldn't be able to do that on your own.

My question to you is: Is this really necessary? And if so, could I have VW do that as well, after I've had the vehicle repaired and made roadworthy again?

Best regards,

Hi,
The wording suggests that you are concerned that coolants of current and past specifications might not be compatible with each other. However, this applies to every coolant change and every top-up with coolant of a newer specification.
Make sure to use coolant with the same specifications as the original. If you can't find the original, don't just drain everything (including from the radiator), but first fill it with distilled water for rinsing (don't forget to bleed the system). I would recommend doing the rinsing while the engine is running, as auxiliary pumps and valves can be controlled with VCDS. If the water becomes discolored, rinse it again. Pure water does not provide corrosion protection, so only leave it in the engine for a short time.
hg
Herbert.

When it comes to replacing the coolant, you can also drive for a few days with "clear water" during the warm or frost-free season. For this application, demineralized water is sufficient. This ensures that no puddle of the "old" coolant remains in any component. Whatever remains after the draining is so heavily diluted by the "clear water" that it no longer matters.

Note on the side: I'm not sure if there are any specific tricks required for bleeding the air from the affected vehicle's system. One of my own vehicles (with a rear engine) needs to... B. To bleed the system properly, position the front slightly higher, and remember that the radiator and heating circuits need to be bled separately.