P0234 Overboost & Dancing Oil Filler Cap

[Wilde]

Hi all,

I'm new to the forum

I've got a T6 102bhp CXGB EUR6 2017

I keep getting the following fault:

Address 01: Engine (2D2D2-CXGB)

2 Faults Found:
23919 - Boost Pressure Regulation
P0234 00 [01100000] - Limit Exceeded (Overboost Condition)
Intermittent - Not Confirmed - Tested Since Memory Clear
Freeze Frame:
Fault Priority: 2
Fault Frequency: 3
Mileage: 238700 km
Date: 2026.01.17
Time: 19:32:41

Engine speed: 2711.50 /min
Normed load value: 96.1 %
Vehicle speed: 117 km/h
Coolant temperature: 90 C
Intake air temperature: 7 C
Ambient air pressure: 980 mbar
Voltage terminal 30: 14.570 V
Unlearning counter according OBD: 38
Charge air pressure: specified value: 1.610 bar
Absolute intake pressure: 140 kPa abs
Mass airflow sensor 1 bank 1 airflow: raw value: 670.5 mg/stroke
Exhaust recirc.valve 1 bank 1: posit.feedback - Actual value: -154.23 %
Throttl.valve adapt. 1 bank 1: posit feedback - Actual value: 75.13 %
Turbine actuator 1 bank 1: posit.feedback - Actual value: 15.91 %
Mean injection quantity: 22 mg/stroke
Air cleaner degree of soiling: 16.27 %
Turbocharg.2 compress.outlet: press.sensor 1 bank 1: raw value: 0 mbar
Turboc.1 turbin.bypass valve 1 B. 1: pos.feedback - Actual value: 0.00 %

25955 - Boost Pressure Regulation
P0234 00 [01100000] - Limit Exceeded (Overboost Condition)
Intermittent - Not Confirmed - Tested Since Memory Clear
Freeze Frame:
Fault Priority: 2
Fault Frequency: 3
Mileage: 238700 km
Date: 2026.01.17
Time: 19:32:41

Engine speed: 2709.00 /min
Normed load value: 60.8 %
Vehicle speed: 117 km/h
Coolant temperature: 90 C
Intake air temperature: 7 C
Ambient air pressure: 980 mbar
Voltage terminal 30: 14.570 V
Unlearning counter according OBD: 38
Charge air pressure: specified value: 1.610 bar
Absolute intake pressure: 140 kPa abs
Mass airflow sensor 1 bank 1 airflow: raw value: 673.6 mg/stroke
Exhaust recirc.valve 1 bank 1: posit.feedback - Actual value: -154.23 %
Throttl.valve adapt. 1 bank 1: posit feedback - Actual value: 75.13 %
Turbine actuator 1 bank 1: posit.feedback - Actual value: 15.78 %
Mean injection quantity: 22 mg/stroke
Air cleaner degree of soiling: 16.27 %
Turbocharg.2 compress.outlet: press.sensor 1 bank 1: raw value: 0 mbar
Turboc.1 turbin.bypass valve 1 B. 1: pos.feedback - Actual value: 0.00 %


It only happens when on the motorway at about 120km/h, it even happens when cruise control is on!

Last year I had the turbo replaced, so I can't imagine this is the issue I also replaced the N75, MAF Sensor, Boost Pressure Sensor and MAP sensors

Over the weekend, I was checking the oil and unscrewed the Oil cap and there was a bit of pressure, I've taken a video:

Does this look normal?

I was thinking it could be the PCV, but not sure...

Thanks in advance

 

[mmi]

Please post the following

1) Full VCDS Auto-Scan
2) Engine blockmap - Ignition ON/engine OFF
3) Engine blockmap - Engine running at idle
4) Engine blockmap - Engine running at idle - 3 minutes after startup


How-to create a blockmap file:

[VCDS]
[Applications]
[Controller Channel Map]
- Single Controller Address = 01
- Login or security access code: Leave blank
- Function: Measuring values
- Output: CSV file
[Go]

The result (TXT and CSV) files are saved into directory C:\Ross-Tech\VCDS\Logs
Please attach the files here.

 

[Wilde]

Please post the following

1) Full VCDS Auto-Scan
2) Engine blockmap - Ignition ON/engine OFF
3) Engine blockmap - Engine running at idle
4) Engine blockmap - Engine running at idle - 3 minutes after startup


How-to create a blockmap file:

[VCDS]
[Applications]
[Controller Channel Map]
- Single Controller Address = 01
- Login or security access code: Leave blank
- Function: Measuring values
- Output: CSV file
[Go]

The result (TXT and CSV) files are saved into directory C:\Ross-Tech\VCDS\Logs
Please attach the files here.

Hi mmi,

Thanks for getting back to me and really sorry about slow reply... Life

I ended up getting the rocker cover assy (PCV Valve) and breather pipe replaced. Last week, that stopped the P0234 happening at ~117km/h, I even took it to ~130km/h was fine for a bit then same EML again

I have ran Auto Scan and the blockmaps

Really appreciate your help, this has been plaguing my Van for a while

 

[mmi]

I have ran Auto Scan and the blockmaps (please see attached)

Thanks. Interesting
Do you know the history of the van as I think the engine software is not the factory software? If so perhaps it's asking too much boost, or the limits (max boost) should also be altered.

 

[Wilde]

Thanks. Interesting
Do you know the history of the van as I think the engine software is not the factory software? If so perhaps it's asking too much boost, or the limits (max boost) should also be altered.

Oh right, thanks!

I did get the Van remapped at a reputable place... So maybe asking for to much boost.

Otherwise, did you spot anything?

I used a hand held vacuum pump and the actuator was moving freely. I also ran a turbo charger test through VCDS and everything seemed in order, could hear the turbo spooling up etc.

Cheers

 

[mmi]

I did get the Van remapped at a local (Banbury) reputable place... So maybe asking for to much boost.

I would guess that's the reason for the overboost, or...

I also replaced the N75, MAF Sensor, Boost Pressure Sensor and MAP sensors

What exactly are Boost Pressure Sensor and MAP sensors - were they OEM parts?

Otherwise, did you spot anything?

Well, it looks like that EGR, DPF and AdBlue are all gone, along with at least 5 temperature sensors (now reporting -40 °C)

I used a hand held vacuum pump and the actuator was moving freely. I also ran a turbo charger test through VCDS and everything seemed in order, could hear the turbo spooling up etc.

The movement (min/max) was also captured in the table above (green).

 

[manfrotto]

Based on the above from @mmi , have the EGR, DPF and Adblue been deleted perhaps?

 

[Wilde]

Yeah I'm coming to that conclusion after checking the other things, Vans absolutely fine the rest of the time

MAF, MAP & Boost Pressure Sensors are Bosch and N75 Pierburg. Which I think are OEM

Oh right, looks like they might have been. I'll contact the mapper to get the map changed

Thanks for your help!