Limp mode diagnosis help

[panda-52]

For sometime now my 2002 TDI has been going into limp mode when under heavy acceleration in 3rd gear. It revs easily to red line in the lower gears. Usually this does not set a CEL but when it does the code is for intermittent overboost. This weekend since I was doing an oli change I decided to look further into this problem. The car has 310K miles. I recently changed all the vacuum lines. So I put the mitty vac on the acculator and seemed to get good smooth movement with around 17-18 inch producing maximum movement. I then used the Vag-Com VNT to graph N-75 turbo response. The results consistently indicated more boost than was requested when the turbo was in use. The 2 lines pretty much tracked each other separated by about a tick mark. Except under heavy acceleration when the actual boost increased further and then into limp mode. Since the turbo was obviously responding I assumed it was likely the N-75. To be sure I swapped with the EGR N-75, but unfortunately the car can still be made to go into limp mode a little over 3,000 rpm in third under heavy acceleration. At this point I'm thinking it must be the turbo but have a hard time explaining whats really happening.

BTW the linkage has never been adjusted so that's not likely the problem. Have i missed anything? If it's the turbo is it likely to fail soon or will it continue on like now?

[Keithuk]

The usual thing is bad vacuum lines but you say you've changed all those.

Does a VAG-COM scan show any error codes show?

[panda-52]

Originally Posted by Keithuk

The usual thing is bad vacuum lines but you say you've changed all those.

Does a VAG-COM scan show any error codes show?

Usually it will go into limp mode without throwing a code but not the last time. The code was 16618 - Boost Pressure Regulation, PO234 Limit Exceeded (Overboost Condition) - Intermittent

Yes, no vacuum leaks, all new hoses, new EGR and MAF and new injectors. Pulls really strong till it goes into limp mode.

[kevg]

Sounds like turbo needs removing and cleaning out inside. Disconnect turbo actuator rod and move by hand should feel free. If possible try moving actuator with engine running at 2000rpm to load vanes.

[panda-52]

So my diagnostic approach seems valid and the likely cause at this point is a problem with the turbo? With the number of miles on this car if I have to remove the turbo I'm tempted to just go ahead and replace it with a VNT15 for a mild upgrade. I just don't want to discover after doing that that I overlooked some other obvious cause.

[Keithuk]

VAG Error Code: 16618

Fault Location:
Engine boost condition - limit exceeded

Possible Cause:
Hose connection(s).
Wiring.
Turbocharger (TC) wastegate regulating valve.
Turbocharger (TC) wastegate.


EOBD II Error Code: P0234

Fault Location:
Turbocharger (TC), engine boost condition - limit exceeded

Possible Cause:
Hose connection(s).
Wiring.
Turbocharger (TC) wastegate regulating valve.
Turbocharger (TC) wastegate.

As taken from my Free EOBD II Error Codes software

[panda-52]

I'm confused by your post. I'm pretty sure I don't have a wastegate or wastegate regulating valve. This is a 2002 ALH.

[Keithuk]

Well I'm just saying what those error codes mean. But it looks like I'll have to update that number here.

VAG Error Code: 16618
EOBD II Error Code: P0234

Fault Location:
Turbocharger (TC), Boost Pressure Regulation: Limit Exceeded (Overboost Condition)

Possible Cause:
Malfunction Indicator Light (MIL) ON.
Boost Pressure too high.
Reduced Power Output.

Hoses incorrectly connected, disconnected, blocked or leaking.
Boost Pressure Control Valve (N75) faulty.
Boost Pressure Sensor (G13) faulty.
Turbocharger (TC) stuck/faulty.

Possible Solutions:
Check Charge Pressure Control System.
Perform Output Test (to check the Turbocharger (TC)).
Perform Basic Setting (to check the Charge Pressure Control).
Perform Pressure Test to locate Leaks.
Check/Replace Boost Pressure Control Valve (N75).
Check/Replace Boost Pressure Sensor (G13).
Check/Replace Turbocharger (TC).

[panda-52]

Ok, Thanks.