Can anyone please offer a possible solution to my problem. I have trawled forums for over the last three or four weeks and carried out all the offered solutions. I am now tearing my hair out...........Please help!
DETAILS:
Passat 2002 1.9TDi 100ps
FAULT CODE:
17964 Negative Boost Pressure -163 P1556
SYMPTOMS:
Sudden loss of power - this occurs mainly between 60 And 70mph under load. If you drive it hard at high revs it seems fine, it just occurs when you call for a bit more power at higher speeds, or up a hill.
Switch off and on again, and it resets and your good to go.......until the next time.
POSSIBLE SOLUTIONS CARRIED OUT:
All vacuum hoses replaced.
Vacuum hoses checked for correct configuration - all good.
All vacuum pipes checked - all good.
Vacuum system checked (and checked again) for leaks - all good.
Turbo removed, stripped, cleaned, reassembled and refitted - it is now spotless. Checked the operation with the lever manually - good.
Turbo actuator checked for operation - smooth as silk. I manually pulled a vacuum on it, which it holds indefinitely - good.
Removed and checked vacuum reservoir sphere - good.
Replaced front N75/vacuum control unit with new.
Swapped rear vacuum control unit (at bulkhead) with old N75 from the front (now known to be good) as they have the same part number - no change.
Removed and cleaned EGR valve assembly (now spotless) and checked operation - good.
Replaced MAP sensor with new Bosch unit.
Disconnected MAF and road tested - fault still occurred (so not the problem)
I have checked and double checked everything I have done, I am now out of ideas
Any ideas, thoughts, suggestions or even clues - no matter how small, would be very gratefully appreciated - Many, many thanks in advance. Here's hoping one of you has the answer..............