Right, update...

 

I retested, and found I didn't have voltmeter connected correctly last time.  

 

Here's what I get:

Input voltage to the sensor is about 5v

 

Output voltage at ambient pressure (not running) is 3.9v.

 

Output voltage at tickover is 1.4v

Output voltage after running @2000rpm is 1.3v

 

BUT after stopping the engine, the output voltage within about 10seconds increases again to 3.9v.

 

Obviously without anything to compare it to, I can't tell if these values are correctly calibrated... but it certainly seems like the sensor is working.  It also seems like I do have a vacuum leak.  So checking that is the next step...

 

(Quick question to check though - there isn't an electric vacuum pump at all is there.  I can't see one, but thought I'd check...)

Assuming your foot isn't on the brake pedal at the time you're stopping the engine, that doesn't seem right, as the vacuum level in that section should be retained by the one-way valve just engine-side of the sensor.

No electric vac pump that I know of, but I'll have a quick look at the wiring diagrams to check.

 

Edited 20 October, 20196 yr by Wino

Agreed. It either seems like a leak in the pipework, non return valve, or servo.

 

Why that should cause a fault code suggesting an electrical fault is another matter, but it would certainly explain the restarting issue

Can you take some more photos of that area of the engine bay from various angles.  I'm not clear how your 'misconnected' hoses in another thread relate to this pipework, if at all?

 

 

Good question. I'd hoped that might be the source of the leak. But pushing the joint together made no difference, so I'm still trying to get to the bottom of it. A vacuum test should tell me if it's the pipework/ valve (cheap) or the servo (expensive). Or neither ( confusing!)

If the part number on this matches yours, it might be worth a punt: https://www.audivw24.co.uk/product-eng-31769-HOSE-PIPE-VW-UP-1S0612041C.html

A good visual and physical close-up examination of yours should reveal any splits and cracks, but you'd need to disconnect both ends to test the non-return valve I think.

Ive the same codes but mine is showing sender for gear lever in neutral as faulting. it tells me it's shorting out. given that, could it be sending its 5v across the earth to the brake booster and confusing it? I'm replacing the neutral switch and I'll stay again once the shorting code is gone.

so i replaced my gearbox neutral sender which the ecu said was shorting out and my brake servo fault codes are now gone.  no more codes showing.