P0237 Audi A3 2.0 TDI: Low Signal

Hi, I'm having a strange problem.
Vehicle: Audi A3 8PA, 2.0 TDI 140 hp (BMM), first registration: 09/2006.
Original VCDS Hex+CAN-USB and Hex-Net interfaces from PCI are available!
The vehicle has entered emergency mode, it's no longer accepting fuel, the glow plug indicator is flashing, and the engine has stalled.

Error code:
VCDS version: DRV 26.3.0 is running on Windows 11 x64.
shop.dieselschrauber.org
Address 01: Engine Control Module
Label file: DRV\03G-906-021-BMM.clb
Control unit part number: 03G 906 021 JH. Hardware: 03G 906 021 AB.
Part and/or version: R4 2.0L EDC G000SG 0131.
Encoding: 0000072
Operating number: WSC 30480 001 1048576
VCID: EE9045F9F98AA2EFA1-80BA
2 error codes found:
000567 - Sensor for boost pressure (G31).
P0237 - 000 - Signal too low - Intermittent.
Environmental conditions:
Error status: 00100000
Error priority: 1.
Error frequency: 2.
Lost Count: 255
Mileage: 165,698 km
Time: 0.
Date: 2026.08.06
Time: 13:25:08
Environmental conditions:
Speed: 2352 RPM.
Speed: 124.0 km/h
Last: 0.0%
Voltage: 13.98 V
Binary value: 00101011
Pressure: 561.0 mbar
Pressure: 1275.0 mbar
005522 - Altitude sensor / Boost pressure sensor.
P1592 - 000 - Implausible relationship - Intermittent.
Environmental conditions:
Error status: 00100000
Error priority: 1.
Error frequency: 1.
Lost Count: 255
Time: 0.
Environmental conditions:
Speed: 0 RPM.
Speed: 32.0 km/h
Pressure: 254 mbar.
Pressure: -256 mbar.
Binary value: 00011010
Pressure: 958.8 mbar
Pressure: 693.6 mbar.
Readiness: 1 1 0 0 0

After the engine stall, it restarted, but then stalled again after a few meters.

At home, I replaced the G31 with an original part.
Mass points cleaned and resealed, cable harness (1KD 971 658) installed.

"So far, it runs, but when you demand power, it reverts to limp mode and shuts off. The only error code stored is 'G31 signal too low.' The turbo and DPF were replaced about 40,000 km ago. I've pressure-tested the charge air system and also tested it with a smoke generator, and it's perfectly airtight."

Well, I guess we're left with the MSG, or what do you think?

I'm grateful for any help!

Hello,

Logs should be relevant to the topic.

ECUs and boost pressure sensors rarely fail; it is much more likely that problems arise from the wiring, connectors, or power supply to the ECU.

"A common issue is damage to cables caused by martens, particularly to wires connected to sensors like the turbocharger pressure sensor. Make sure to check all cables, as shorts can affect the entire system."

Best regards, Rainer.

Here's the log again:

I replaced the cable harness from the mass airflow sensor (MAF) to the boost pressure sensor with the original VW part (1KD 971 658).
The remaining cables are not damaged by animal bites or anything similar.
The contact points were thoroughly cleaned and resealed with wax.
The old sensor was definitely faulty, showing a difference of over 50 mbar between the MSG sensor and the G31. The MSG sensor read 979 mbar, while the G31 read 1080 mbar. With the new sensor, both values are now almost identical. And the second error is no longer appearing either.

Subject: Power Supply.
Where should we start?

So, are there any more error codes stored now?

Does the glow plug come on and then the engine dies?

Currently, the error signal appears to be too small. The signal height indicator has not reappeared since I installed a new sensor.

Well, the intermittent "boost pressure sensor signal too low" indication suggests interruptions in the wiring to the boost pressure sensor's power supply or its signal line.

It's also important to check the sensor's wiring to see where it's routed, as a short circuit to ground, for example, due to damaged cable insulation, will also prevent the sensor from generating a signal.

Have you already checked the wiring harness directly at the control unit?

I just installed a different MSG (Multi-Sensor Gateway) that is 100% functional, and it exhibits the same behavior as the original MSG.

I'm in second gear, accelerating to approximately 3500 RPM, I release the accelerator and let the engine coast for a short time. As soon as I press the clutch, the engine stalls. I turn the ignition off and on again, the glow plug indicator flashes, and error code P0237 is stored in the memory. The measured value for boost pressure (MWB 11) remains at 2193 mbar for a while, until everything returns to normal. Then I can clear the error code, and the engine starts immediately again.

"It also states that a value of 2193 mbar is displayed when the G31 is disconnected."
So, somewhere along the line, the connection or signal is breaking down.
The question now is, where do we start searching, and according to what system?

The wiring harness from the MSG (Modular System Garage) to the sensor is definitely okay, as it's completely new and original VW. So, there must be something wrong somewhere else in the wiring harness...

Hi.

Engine control unit wiring harness.

Run VCDS and, for example, log a measurement value such as the ECU supply voltage.

If the voltage drops or the power supply fails, the ECU will no longer receive power.

Best regards, Rainer.

Hi Rainer,

Okay, that's how I'm going to proceed, and then I'll examine the entire engine wiring harness piece by piece.

So, I've just had a new realization!
The entire engine wiring harness has been thoroughly checked, and everything is in order.
N75 has been replaced, but the error persists.
Then, by chance, I noticed that the intercooler hose connecting the intercooler to the intake manifold completely collapses exactly when the error occurs, effectively cutting off the airflow.

I checked the small red hose at the turbo outlet; it's a bit soft, but not damaged inside. I read that sometimes the inside of the hose can swell, which can cause exactly this effect.

Now, the problem is no longer related to the electrical components.
Any suggestions by chance?

Hello, I'm not entirely sure which hose you're referring to, but I assume it's the one connecting the low-pressure fuel pump to the intake manifold?

If it retracts, then something is either blocking the inlet of the coolant system or somewhere within the intake system.

Did you forget to remove the cleaning cloths from the air filter housing?

I'm referring to the part with the number 3C0145828K, which is located directly on the turbocharger (driver's side, near the air filter).
He is mentioned as the cause in various forums.

The hose that runs from the coolant reservoir to the plastic pipe (located on the passenger side, at the front of the strut tower) – which passes under the fuel lines and then connects to another hose in a 90-degree bend that goes into the engine – appeared to be visibly constricted (I couldn't see the small hose as described above at that moment because it was obstructed).

There is no foreign object or similar material present that could cause a blockage.

Hallo,

There is always excessive pressure in this hose.

Wenn er sich zusammenzieht, hat er sich innerlich aufgelöst und verstopft sich selbst oder ein Putzlumpen o.ä. verstopft die Ansaugseite vom Lader. Weil in dem Fall der Lader schon hin wäre, sehe ich die Verstopfung im Luftfilterkasten zum Gitter vor dem LMM oder schon in der Zuluft zum Luftfilterkasten.

Best regards, Rainer.

It's working again!
It was that red hose I mentioned earlier!

This hose carries the charge air from the turbocharger towards the intercooler and the engine, and it can potentially leak (or burst), which would naturally lead to a loss of pressure, reduced performance, and limp mode. However, it cannot constrict itself to that extent without a prior blockage in the airflow. If the engine is running in suction mode due to a fault, there will be a vacuum in the intake path, which can be observed by a slight contraction of the air-carrying hoses. If it's completely sealed, the hoses (which are likely fabric hoses!) will probably become soft and burst soon. You probably temporarily fixed a second defect, or rather, swept it under the rug. I would replace the hose that is visibly constricted.
hg
Herbert.