2001 Audi A4 P1555 code

LenoVan

Member
Joined
Apr 26, 2022
Location
Canada
TDI
A4
I have bought this car last year. Yesterday when I derived it nearly 10KM, step on the accelerator but kept nearly 2000.
I stop and restart, the accelerator is working, but when I derived 2km, the situation happened again.
After the next day, when I start the car, some smoke comes near the Three-way catalyst.

This is the error Code.
What should I do the check the car and repair it?

17963/P1555 - Boost pressure Control: Upper Limit Exceeded
Possible Symptoms

  • Reduced power output
  • Limp mode
Possible Causes
  • Boost Pressure too High
  • Hoses/Pipes incorrect connected, disconnected, blocked or leaking
  • Charger Pressure Control defective
    • VNT (variable nozzle turbo): nozzles stuck
  • Solenoid Valve for Boost Pressure Control (N75) defective
Possible Solutions
  • Check Hoses/Pipes to/between Components
  • Check Solenoid Valve for Boost Pressure Control (N75)
  • Check / Clean / Replace Charge Pressure Control
    • Check / Clean mechanism for variable nozzles
 

Scubanero

Veteran Member
Joined
May 30, 2007
Location
Calgary AB
TDI
2005 Passat Wagon
What you are seeing is turbo limp mode. Since it appears to be high pressure, not low, you need to look at the controls and the inlet vanes. There are lots of threads dealing with similar problems. Search and you will find.
 

LenoVan

Member
Joined
Apr 26, 2022
Location
Canada
TDI
A4
What you are seeing is turbo limp mode. Since it appears to be high pressure, not low, you need to look at the controls and the inlet vanes. There are lots of threads dealing with similar problems. Search and you will find.
Thanks for your response.
Two months ago, When I derived the car the engine light was on, and the engine passenger side has caught fire. I guess the reason is the high temperate in the three-way catalyst and some oil upon it.
After this accident, I replaced MAF, the oxygen sensor.
Today the same thing happened again. I have searched in many forums, the most answer is the Hoses leak, but when this leak happens,
Boost Pressure too High can't be high. I am very confused.
 

Scubanero

Veteran Member
Joined
May 30, 2007
Location
Calgary AB
TDI
2005 Passat Wagon
Failure of the inlet guide vane control will also trigger a limp mode. In that case, look into the N75 relay and associated vacuum tubing.
The other possibility is that the vanes are corroded and stuck in place.
 

LenoVan

Member
Joined
Apr 26, 2022
Location
Canada
TDI
A4
Failure of the inlet guide vane control will also trigger a limp mode. In that case, look into the N75 relay and associated vacuum tubing.
The other possibility is that the vanes are corroded and stuck in place.
Thanks. I have checked the N75 and associated vacuum tubing.it's ok.
So air leak is not the reason for "P1555 - Boost pressure Control: Upper Limit Exceeded" ?
The pressure cannot be discharged, so the pressure is too high, rather than the leakage of the pipeline, which needs to be supplemented?
 

zzdiesel

Veteran Member
Joined
Dec 10, 2010
Location
sask. mostly now Wa.
TDI
05 passat tdi Geared BSM and Bewcam 2nd 2005 deleted ,converted and bew cam stage 2 Malone3 tune.
There have been known to be problems when the vac tubing was routed incorectly, particularly at the N75.
 

Scubanero

Veteran Member
Joined
May 30, 2007
Location
Calgary AB
TDI
2005 Passat Wagon
Possible Causes
  • Boost Pressure too High
  • Hoses/Pipes incorrect connected, disconnected, blocked or leaking
  • Charger Pressure Control defective
    • VNT (variable nozzle turbo): nozzles stuck
  • Solenoid Valve for Boost Pressure Control (N75) defective
Possible Solutions
  • Check Hoses/Pipes to/between Components
  • Check Solenoid Valve for Boost Pressure Control (N75)
  • Check / Clean / Replace Charge Pressure Control
    • Check / Clean mechanism for variable nozzles
 

MEgearhead

Veteran Member
Joined
Aug 6, 2016
Location
Virginia
TDI
B5.5, 4L, 4G
The first step should be to connect a hand vacuum pump to the turbo actuator and see that it moves smoothly through it's range of motion with increasing vacuum.

If it doesn't, the mechanism needs to be cleaned.

If it does, remove the hand pump and reconnect the vacuum hose then run the turbo actuator test using VCDS and see if it moves from stop to stop. If the actuator works with a hand pump but not automatically during the test the issue is in the vacuum control. Verify the vent line is not plugged. If not then try a known good N75 valve.
 

LenoVan

Member
Joined
Apr 26, 2022
Location
Canada
TDI
A4
The first step should be to connect a hand vacuum pump to the turbo actuator and see that it moves smoothly through it's range of motion with increasing vacuum.

If it doesn't, the mechanism needs to be cleaned.

If it does, remove the hand pump and reconnect the vacuum hose then run the turbo actuator test using VCDS and see if it moves from stop to stop. If the actuator works with a hand pump but not automatically during the test the issue is in the vacuum control. Verify the vent line is not plugged. If not then try a known good N75 valve.
The VCDS shows 'boost pressure control(N75)' values is always 0, the "boost pressure(actual)" and "boost pressure(specified)" value didn't change with the engine speed .
so this means I need a new N75?
 

LenoVan

Member
Joined
Apr 26, 2022
Location
Canada
TDI
A4
Does the vacuum actuator move from fully extended to the stop screw when vacuum is
Does the vacuum actuator move from fully extended to the stop screw when vacuum is applied?
I can’t see the status because only check by myself. So I need see the vacuum actuator status when the engine speed is high?
When the engine speed is high, there is some smoke came out near three-way catalysis, I don’t know why.
 

MEgearhead

Veteran Member
Joined
Aug 6, 2016
Location
Virginia
TDI
B5.5, 4L, 4G
Get a hand vacuum pump. Connect it to the turbo actuator with the engine off. Pump the vacuum pump and see if the actuator moves.
 

LenoVan

Member
Joined
Apr 26, 2022
Location
Canada
TDI
A4
Get a hand vacuum pump. Connect it to the turbo actuator with the engine off. Pump the vacuum pump and see if the actuator moves.
If the actuator doesn’t work, the n75 value is 0?
video Here is the record, Maybe the oxygen sensor also has a problem.
 
Last edited:

MEgearhead

Veteran Member
Joined
Aug 6, 2016
Location
Virginia
TDI
B5.5, 4L, 4G
The turbo is doing exactly what the ecu is telling it to do - provide no boost. Is this after driving it until it goes into limp mode? If yes, that information is not very helpful. Once the car goes into limp mode N75 will remain zero, and actual, specified, and atmospheric will be close.

Once you shut the car off and restart it, limp mode should clear.

What are all the active fault codes?
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
LOL.... what engine is in this car? This is a TDI site, and there were no diesel Audi A4s sold here in 2001, or ever. In 2001, the Audi A4 got the 1.8t gas engine, code AWM. Which shares virtually nothing with any TDI.

The wastegate may be physically stuck shut, or the mechanism that controls it is.
 

MEgearhead

Veteran Member
Joined
Aug 6, 2016
Location
Virginia
TDI
B5.5, 4L, 4G
I was assuming it was a European model similar to ours. But, you're right the engine code would be considerably helpful.
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
Well, he is in Canada, which is not part of Europe although it certainly could be a gray market import. However, you'd think he would have mentioned that, but also mentions '3-way-catalyst', which TDIs don't have, so.....
 

MEgearhead

Veteran Member
Joined
Aug 6, 2016
Location
Virginia
TDI
B5.5, 4L, 4G
You have likely identified the root cause of all the confusion. Would be nice to know exactly what engine it is.
 

MEgearhead

Veteran Member
Joined
Aug 6, 2016
Location
Virginia
TDI
B5.5, 4L, 4G
OH nailed it. You are posting on a site dedicated to diesels, in the forum for the 2004-2005 Passat 2.0 TDI. That's why all our responses are confusing. Oilhammer's suggestion to look at the waste gate is your best option presented here. You might head over to audizine, audiworld, audiforums, or the ross-tech forums. I'm going to bow out since I will not be any help for your model. Hope you get it sorted out!
 

LenoVan

Member
Joined
Apr 26, 2022
Location
Canada
TDI
A4
OH nailed it. You are posting on a site dedicated to diesels, in the forum for the 2004-2005 Passat 2.0 TDI. That's why all our responses are confusing. Oilhammer's suggestion to look at the waste gate is your best option presented here. You might head over to audizine, audiworld, audiforums, or the ross-tech forums. I'm going to bow out since I will not be any help for your model. Hope you get it sorted out!
Thank everyone for every serious reply, especially to you. I am a new user here so it caused everyone to be troubled by this situation.
 

LenoVan

Member
Joined
Apr 26, 2022
Location
Canada
TDI
A4
Well, he is in Canada, which is not part of Europe although it certainly could be a gray market import. However, you'd think he would have mentioned that, but also mentions '3-way-catalyst', which TDIs don't have, so.....
Thank you. this is a 2001 Audi a4 1.8T in Canada. so "The wastegate may be physically stuck shut, or the mechanism that controls it is." may be the reason?
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
Yes, and on that engine, the actuator rod is in an awkward to see place, up against the engine kind of down low.

If you do a google image search for "AWM 1.8t turbocharger" you can see the little round servo with the rod attached. You need to see if that moves freely.

Not sure where in Canada you are, but if that car has been subjected to 21 years of road salt, especially if it has spent any of that time missing its underneath shield protecting the engine, then you will have a rusty mess on your hands. The mechanism could be stuck, the little servo can could be rusted out, who knows.
 

LenoVan

Member
Joined
Apr 26, 2022
Location
Canada
TDI
A4
Yes, and on that engine, the actuator rod is in an awkward to see place, up against the engine kind of down low.

If you do a google image search for "AWM 1.8t turbocharger" you can see the little round servo with the rod attached. You need to see if that moves freely.

Not sure where in Canada you are, but if that car has been subjected to 21 years of road salt, especially if it has spent any of that time missing its underneath shield protecting the engine, then you will have a rusty mess on your hands. The mechanism could be stuck, the little servo can could be rusted out, who knows.
You are right. I am living in Vancouver. This car only has 120k KM. There are so much oil inside the engine, so last year, because of the limp mode, it was on fire.
 
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