Limp Mode - Boost Pressure Query

[Drobbo]

Hello, My 2015 model Scirocco 64 plate 2 litre diesel GT, went into limp mode recently. I had managed to get home luckily. Loaded up VCDS and did a scan for faults, the glow plug light was also blinking at me.

VCDS was displayed as below:

Address 01: Engine (J623-CUUB) Labels:. 04L-907-309-V1.clb
Part No SW: 04L 906 016 ED HW: 04L 907 309 G
Component: R4 2.01 TDI H21 2041
Revision: 88H21- CVN: 4FBE1A52
Coding: 01190012040501090000
Shop #: WSC 55451 004 1048576
ASAM Dataset: EV_ECM20TDI01104L906016ED 001005
ROD: EV_ECM20TDI01104L906016_001_VW32.rod
VCID: 6FBBC5A0471BBE82BE9-803A VINID: 9E69EAAAA043A96980007242040E0CAD73
1 Fault Found:
11901 - Manifold Pressure / Boost Sensor (G31)
P0236 00 [00100000] - Implausible Signal
Intermittent - Not Confirmed - Tested Since Memory Clear
Freeze Frame
Fault Priority: 2
Fault Frequency: 1 Mileage: 99761 km
Date: 2024.06.21
Time: 12:40:41
Engine RPM: 0.00 /min Normed load value: 0.0 % Vehicle speed: 0 km/h Coolant temperature: 90 °C
Intake air temperature: 70 °C
Ambient air pressure: 1000 mbar Voltage terminal 30: 12.380 V
Unlearning counter according OBD: 40

I went to a VW parts shop and they assured me that the sensor I had originally in my car was not available now, and supplied one with two pressure hoses instead of one like the original. I have blacked one of the hose pipes off and put the pressure pipe on the other side. It looks similar to the DPF differntial pressure sensor to me but I am not sure.

Since driving it again, the power does not feel the same, it feels like the boost is not as much and takes longer to accelerate.

Anyone had these issues with a Scirocco before 2.0 Diesel 2014/2015?

Cheers

[bigkris06]

Are you getting any codes or glow plug light now?
Do you still have the old part? Take the part numberd and cross reference it with the new one,
You may have been supplied an incorrect part so worth checking
If it is correct I suspect the part has been superseded to cover other models now and some use both and some only use the one. May I ask what you used to blank the other off? The symptoms you are describing does sound like you may be losing vacuum but I could be wrong.
.

[Drobbo]

The part he supplied is completely different, I believe it’s a differential pressure sensor for the EGR he must have got his wires crossed but I will match it with the same one online as there’s OEM ones available. The reasoning behind it was because it measures the pressure still, BUT, I’m not sure it will work 100% as I think it just masks the problem. I blanked it off with a rubber cap and a zip tie.

Also drove home today again after and I lost approximately 25% power with the glow plug light flashing at me again.

Another VCDS scan picked up on a EGR excessive flow, which was not there when the original pressure sensor was fitted, but since I fitted the part the VW guy game me, (DPF differential pressure), I believe that is what has flagged this issue up.

VCDS scan has now picked up on a glow plug pressure sensor which apparently are integrated on the glow plug for cylinder 3. And funnily enough VCDS located it was cylinder 3 that was having the intermittency guiding towards that can be one of the issues I have. I will keep the forum updated but any other ideas or agreements with me I will massively appreciate it .

[bigkris06]

Do you have the original part? If so get the part number and do a search for that, I’m not 100% sure but if the egr system's also uses the vacuum system it may cause the additional issues you were having, it’s certainly a massive coincidence that it only started after you changed that part.
My advice would be sort the original problem and go from there.

[Drobbo]

I will get the glow plug replaced anyhow, it can’t do much harm to do all four whilst I’m there, and then I will put the original boost pressure sensor in and see how it runs, if it persists I will then replace the boost sensor with one that’s has the same part number on it or a replica which has been made as they’re discontinued now.


Then I will test drive for a while or until my car has another tantrum, and if it does then I will investigate air leaks/smoke test the vacuum system. Is that what you’d suggest? Smoke testing? Cheers.

[bigkris06]

You need something like a mityvac (Amazon do a cheaper version that works pretty well) it pressurises the system and if it holds the pressure then that’s okay,
I would be inclined though still to Google the part number for the original sensor though and get a replacement before you replace anything else.
The other thing to ensure is that the pipe you blanked was the correct one and that it is securely blanked.

[Drobbo]

Hello,

I’m back, exact same fault returned, I changed the glow plugs, including the cylinder 3 glow plug with integrated pressure sensor, and this has not been resolved… YET.

BUT… I finally have clearance, after scanning and doing multiple tests, and researching the fault and the similar symptoms from other people having the same issues on YouTube etc, (glow plug light flashing) does not always mean the glow plugs are faulty, however I am happy that I have replaced them all anyway, because it is a serviceable part and I will not have to worry about it for a while, hopefully.

Anyway, the G31 fault as seen in my original thread post, points to the manifold boost pressure sensor located in G31 on the workshop manual, and I have ordered another G31 Manifold boost pressure sensor and this has to be the issue, my theory is that because the underlying issue of this sensor throwing intermittent signals and sometimes even high signals, it is confusing the glow plug pressure sensor as some of the readings and pulses given from this boost sensor to the glow plug pressure sensor in cylinder three are not corresponding, therefore the sensor is more than likely faulty. No air leaks or boost leaks anywhere after tests.

I will update this forum once I have 100% diagnosed this issue.

Cheers

[bigkris06]

Glow plug light flashing acts as an engine management light so if it does flash you need to scan the car.
Hopefully the new part will resolve your issue.