Passat 2007 Passat B6 boost pressure overboots then limp home

leckylee

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Hi I wonder if anyone can help pleas.

I have a 2007 Passat 2.0 TDI BKP.

The car itself is ace and drives fantastic but just recently it has started to flash (engine fault garage) on the dash and then the glow plug light flashes, if you stop and turn the engine off and on it then drives fine. This happens when you put you foot down and never happens in to when doodling about.

I scanned it with VCDS an it came up with the fault 000564 - Boost Pressure Regulation/P0234 - 006 - limit exceeded (overboots condition) - Intermittent - MIL on

I took it out today to gather some data on actual boost and specified boost an interestingly enough when driving around town it stays more or less steady, however when you put your foot down the actual boost is somewhat higher, when the fault appears there is an almost vertical line on the graph of the specified boost and then both the specified and the actual boost then drop to the bottom of the graph and then you have limited power as expected as I'm presuming that the ECU has gone into limp home mode.

Has anyone experienced this before?

I would be very grateful for any assistance.

Lee
 

leckylee

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Thanks Crasher for coming back so quickly, Just so I understand why does it crash out intermittently? and why does the ECU go mental all of a sudden, I do understand that the turbo veins may be stuck but don't understand why it drives for ages before it goes into limp home mode
 

Crasher

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It is random as the carbon comes away and the clearances change with temperature, the ECU goes into limp mode to protect the engine and turbo from damage.
 

Keithuk

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First posts normally go in introductions else you could get a free fix and we never see you again!!!

VAG Error Code: 16618/000564
EOBD II Error Code: P0234

Fault Location:
Boost Pressure Regulation - Limit Exceeded (Overboost Condition)

Possible Cause:
Malfunction Indicator Lamp (MIL)(K83) active.
Boost Pressure too high.
Reduced Power Output.

Hoses incorrectly connected, disconnected, blocked or leaking.
Solenoid Valve for Boost Pressure Control (N75) faulty.
Manifold Pressure/Boost Sensor (G31) faulty.
Turbocharger stuck/faulty.
Exhaust Gas Recirculation (EGR) Valve blocked.

Possible Solutions:
Check Charge Pressure Control System.
Read Measuring Value Blocks (MVB).
Perform Output Test (to check the Turbocharger).
Perform Basic Setting (to check the Charge Pressure Control).
Difference of set value boost pressure vs. altitude sensor signal > 200 - 1275 hPa.
Perform Pressure Test to locate Leaks.
Check/Replace Solenoid Valve for Boost Pressure Control (N75).
Check/Replace Manifold Pressure/Boost Sensor (G31).
Check/Replace Turbocharger.
Check and clean Exhaust Gas Recirculation (EGR) Valve.

Description:
The boost pressure sensor responds to pressure changes in the intake manifold. This pressure is created by the turbocharger and changes with accelerator pedal position and engine speed. The Engine Control Module (ECM) uses this information to assist in diagnosis of the barometric pressure (BARO) sensor and to provide engine overboost protection. The boost pressure sensor has a 5-volt reference circuit, a low reference circuit, and a signal circuit. The Engine Control Module (ECM) supplies 5 volts to the boost pressure sensor on the 5-volt reference 2 circuit, and provides a ground on a low reference circuit. The boost pressure sensor provides a signal to the Engine Control Module (ECM) on a signal circuit relative to the pressure changes. The Engine Control Module (ECM) monitors the boost pressure sensor signal for voltage outside of the normal range. The Engine Control Module (ECM) calculates a predicted value for the boost pressure sensor. The Engine Control Module (ECM) then compares the predicted value to the actual signal.

As taken from my new EOBD II Fault Codes Software

Thread moved to the correct section as its not a general question. ;)
 

Surfeit

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Bit late to the party.

I've experienced the sudden onset of limp mode in my 2006 Passat 2.0 TDI (BKP) when pushing on hard. Would agree with the diagnosis that the Turbo is at fault.

Carbon build up in the variable vanes coupled withactuator arm wear results in discrepancies between what the ECU expects so see with respect to pressure and air flow and what the turbo can deliver. Got used to resetting on the move for a while (not a safe thing to do and definately not recommended). Using better quality fuels and additives changed the revs and speeds at which the limp mode kicked in.

Changing the Turbo fixed the problem.
 

Crasher

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It can also, because it is water based, cause corrosion of the turbine shaft and its piston rings which if the turbo is old and worn, can cause it to dump its oil into the exhaust. Professional turbo cleaning kits that employ the same idea (Caustic, Sodium Hydroxide) have a solvent based flush which helps flush the water out. From personal experience of doing the job and seeing other people’s results, I won’t recommend it.
 
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