Someone with VCDS - A quick Low Fuel Pressure check for me please.

[IanH755]

Hi all,

Could some kind soul with VCDS please check something for me in the fuel system for both ECU 1 and 2 as I'm seeing something odd on mine and I wonder if its the cause of my current breakdown.

In both ECU 1 and 2 I'm looking for the following two readings in Advanced Measurements, both before starting the engine, and when the engine is running -

Current Fuel Pressure = should read XX.XX BAR
Fuel Pressure Regulator = should read -XXXX

On ECU 1 I'm reading 6.70bar (which changes when cranking) for the Current Fuel Pressure and the Regulator is -217 (which changes when cranking) with the engine OFF.
On ECU 2 I'm reading 12.00bar (which does NOT change when cranking) for the Current Fuel Pressure and the Regulator is -2500 (which does NOT change when cranking) with the engine OFF.

There is only 1 low fuel pressure sensor (G410) which is only connected to ECU 1 (J683) according to the wiring diagrams, and therefore if ECU 1 is getting a "good" reading then I don't know if both ECU's "should" be reading the same pressure and therefore both ECUs can control the pressure, or if only ECU 1 actually controls the low fuel pressure and ECU 2 just gets a NULL signal. I know mine looks like ECU 2 is reading NULL and I don't know if its getting a bad signal (12.00bar seems like the max reading of that sensor) of if thats how its supposed to work. I wonder if ECU 2 being unable to adjust the pressure with the Regulator has caused it to go into a safety shutdown or something similar or if its got nothing to do with it and its how the system should work and my fault lies elsewhere.

Many Thanks for the help!

[alex.r]

Hi Ian,
Below you have the readings from my car. As you said, there is only 1 low pressure sensor, so my logical guess is that since the ECU's are in a master-slave setup, the 2nd once can't get a reading from that sensor.

ECU1:

ECU2:

[IanH755]

Awesome, thanks for that, kind of confirms the "only ECU 1 gets the signal" theory for me and means my fault must still lie elsewhere.

I swear if this is just a fuse issue I'll be upset

[alex.r]

No problem mate! Just out of curiosity, what error codes do you get ? An autoscan post might be interesting...

[IanH755]

I scanned it about 2hrs after the breakdown and there is literally no codes, that's the interesting bit.

Since it's been a week, and I hadn't driven if for the week before, it's now understandably getting some low voltage codes, there's a code for the G85 steering angle as we moved the steering with power off (it's registered in ECU 1+2, ABS controller and backup cam) , and there's always been one since I bought it for no/missing adaption of the instrument cluster.

Outside of that, nothing. I know it's got fuel and air via VCDS so that just leaves the ECUs causing a missing Spark for some unknown reason but with no fault codes to confirm it's difficult to say for sure.

I'll post a log after I finish work.