N75 Issues

Got a customer's car in for a manual swap and having N75 issues. Not sure how the car ran beforehand, but I'm fairly sure it is unrelated. The car will not run the N75 output test. It goes from 5% duty cycle to 55% for a 1/2 second then back to 5%. It doesn't evey try to run the output test correctly.

All the vacuum lines were replaced and tried a separate n75 that was known good. Appears to me to be electrical related and not vacuum or n75. Thought the we might of messed up the manual swap wiring, but it was all fine.

Anybody have the pin outs of the n75 control for the B5 and wire routing? What should the signal look like.

We actually thought about the same thing. Not sure what the result was. Anybody have pin outs/wire colors?

red/white wire on N75 goes to the power supply side (common with a bunch of other stuff*, should just be fixed 12v with key on)

brown/yellow wire is what the ECU uses to pulse ground to N75, that goes to pin 29 of the 60 pin connector at the ECU.



*red wire on pin 2 of throttle flap, red/green wire of crankcase breather heater, and other items, all feeds of of 15A fuse S116.

Wiring diagram sent. Check your e-mail

Thanks guys so far. Well the plugs are not swapped.

Guess when I have a second pair of hands tonight Ill see if I'm getting the constant 12v and the ground is pulsing. I am assuming its not based on the feedback VCDS is giving.

You can easily run the Output Test in VCDS for the N75 with the engine idling and watch the VNT actuator move up and down (since on the BHW it is arranged where you can easily see it from the top).

But since you say it won't run the test, you won't see anything change at the actuator?

I've seen a lot of pinched wires due to quickie lube morons that feel the need to check (and thus mangle) the air cleaners on these cars. Check that harness that runs across the air cleaner to the MAF, N75, and vent heater as that is the common spot they get messed up.

Also, is the ECU flagging any DTCs? If not, if you unplug the N75 and start the engine, will it flag a DTC then?

Correct I even hooked the N75 to a vacuum gauge. The pump is supplying 20-25#. The output of the N75 is 0.

Codes before I started working on it:

3 Faults Found:
17057 - Cylinder 3 Glow Plug Circuit (Q12)
P0673 - 000 - Electrical Fault
Freeze Frame:
RPM: 0 /min
Torque: 174.0 Nm
Speed: 0.0 km/h
Load: 0.0 %
Voltage: 11.93 V
Bin. Bits: 00001000
Temperature: 27.0°C
Bin. Bits: 00110000

16485 - Mass Air Flow Sensor (G70)
P0101 - 000 - Implausible Signal
Freeze Frame:
RPM: 2016 /min
Torque: 0.0 Nm
Speed: 116.0 km/h
Temperature: 38.7°C
(no units): 28.8
(no units): 1.14
Temperature: 92.7°C

16566 - Fuel Temp. Sensor A (G81)
P0182 - 000 - Short to GND - Intermittent
Freeze Frame:
RPM: 882 /min
Torque: 24.0 Nm
Speed: 0.0 km/h
Load: 0.0 %
Voltage: 13.38 V
Temperature: 57.6°C
Temperature: 86.4°C
Temperature: 125.1°C

Readiness: 1 3 0 0 0


New implausible brake pedal code showed up that I need to look into.

Well the glow fault and the fuel temp fault shouldn't have anything to do with the boost control, but the MAF issue might. Although even if the ECU stopped mapping boost and essentially shut the output to the N75 off due to a MAF problem, you'd still think it would operate during the output test mode KOEO.

Did you decide which side of the N75 is missing, power or ground?

Thanks Brian and Paul for your help. The N75 was not getting power, which led to the S116 being blown. It blew only when clutch switch was plugged in.

Turns out I was off one pin in the ECU with the kickdown grey wire. That was a royal pain in the ass.

Awesome, glad you got it fixed. As I posted before, that fuse feeds various things, I forget what all it does but it isn't just the N75.

Oil hammer what will cause to blow the fuse next to the ECM that powers the n75 valve?

How do I find this fuse? Think I may have the same problem.

It is in the ECU Box.

Nash_TDI said:

It is in the ECU Box.

Click to expand...

thanks. And is it after the 126 relay I suppose?