Boost issue, electrical issue, ECM issue???? Advise Needed.

[srane4213]

Hi all.

I have an Octavia Mk1 1.9 Tdi ALH. Recently the car started going into limp mode at higher revs or under heavy load conditions.
All is good cruising with minimal throttle input but as soon as you floor it and the car reaches revs of 1900+ suddenly there is no boost.
I scanned the car using vcds and these are the codes the car is throwing;

Sunday, 05 September 2021, 14:17:07
VAG-COM Version: Release 409.1-US

Control Module Part Number: 038 906 012 HA
  Component and/or Version: 1,9l R4 EDC 0400SG  4922
           Software Coding: 00002
            Work Shop Code: WSC 12345
           Additional Info: TMBCGG1U75A031136     SKZ7Z0E2928713
6 Faults Found:
18057 - Powertrain Data Bus: Missing Message from ABS Controller
        P1649 - 35-00 - -
17954 - Boost Pressure Regulation Valve (N75): Short to Plus
        P1546 - 35-10 - - - Intermittent
17957 - Boost Pressure Regulation Valve (N75): Open or Short to Ground
        P1549 - 35-10 - - - Intermittent
18062 - Please check DTC Memory of Instrument Cluster
        P1654 - 35-00 - -
18065 - A/C System Input/Output Short to B+
        P1657 - 35-10 - - - Intermittent
17946 - Fuel Shutoff Solenoid (N109): Open or Short to Ground
        P1538 - 35-10 - - - Intermittent
---------------------------------------------------------------------------

 

Now, I swapped the N75 and the EGR (N18 I guess), no change.....but cycling the the key (off and on quickly) used to restore the car to normal for a few moments.

Checked for vacuum leaks and found the pipe going to the brake booster had cracked (pic attached for you reference).
Changed the pipe and still the same issue persists. But while fiddling around with the N75, it felt like the solenoid was not getting enough voltage (kind of like a vibrating relay).
So, checked the supply at the connector which goes to the N75. now since I didn't have a Multimeter at hand used a test lamp....and the test lamp was flickering.
So I thought it must be a bad ground somewhere, and took the positive supply form the N75 connector and negative from a good ground point on the engine.
The test lamp was nice and bright without flicker in this case, so provided a good ground to the N75 connector and connected it to the N75. Now, the car runs as it should but the CEL is still popping up and VCDS is throwing these codes;

Sunday, 05 September 2021, 17:07:45
VAG-COM Version: Release 409.1-US

Control Module Part Number: 038 906 012 HA
  Component and/or Version: 1,9l R4 EDC 0400SG  4922
           Software Coding: 00002
            Work Shop Code: WSC 12345
           Additional Info: TMBCGG1U75A031136     SKZ7Z0E2928713
4 Faults Found:
18062 - Please check DTC Memory of Instrument Cluster
        P1654 - 35-10 - - - Intermittent
17946 - Fuel Shutoff Solenoid (N109): Open or Short to Ground
        P1538 - 35-10 - - - Intermittent
18057 - Powertrain Data Bus: Missing Message from ABS Controller
        P1649 - 35-00 - -
17957 - Boost Pressure Regulation Valve (N75): Open or Short to Ground
        P1549 - 35-10 - - - Intermittent
---------------------------------------------------------------------------

Also since I thought the ECM was not getting a good ground I cleaned up the ground points below the battery, and the one near the ECM.

Any ideas as to what might be wrong? Also, will providing a ground to N75 connector harm the ECM?

Thanks.