P1556 fault......yes, another one

I've done some searching on the threads regarding this fault but can't find one that is similar to mine. The car has no boost of course. I applied vacuum to the actuator and verified that it moves. Performed basic setting in mvb 11 and the rod does not move. I switched the n75 with the egr valve and same thing. I don't even hear it turning on. Found that it has power and the ecm is activating the ground. I even checked the wire from the n75 to the ecm and found .2 ohms. I know my dad replaced the valve on the brake booster hose because he thought it was causing the hard brake pedal after applying the brakes a couple of times. Can a lack of or no vacuum cause the n75 not to turn on ? Am I not hearing it turn on because there is no vacuum there to actually activate it ? I'm stumped.

Measure the vacuum source entering the N75. This can be done by just plugging in a mityvac, which it sounds like you have. There is a one-way check valve upstream of the N75 that prevents the vented N75 air from entering the rest of the vacuum system. These can get stuck closed.

thanks for the advice. I'll look at it and update asap.....seems I have posted this twice. Oops

Also a common issue is the nipple of the vacuum pump leaking. My car when you reved it under load the little bit of engine movement would cause it to leak.


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i must have accidentally posted this twice so sorry guys. i'll reply to both of them. i replaced the one way check valve that is inline with the n75 valve and it did the same thing. so i checked for vacuum going to the valve and i have 0.....i checked for vacuum coming out of the pump at the valve on the booster line and found the vacuum all over the place. from like 5 - 20 inches of vacuum. it would tend to stay at 15 inches when i would move the nipple of the pump in a certain spot. but the vacuum changes dramatically when messing with the nipple so, that is going to be replaced. 2nd, i am not getting any vacuum to the reservoir. don't know why since i do get vacuum out of the brake line. there's a T-connection on the n75 valve, no vacuum there. then that vacuum line appears to go into the firewall. i ran out of daylight so i couldn't trace it. i'm going to have to check it in the next couple of days. just wanted to give an update here. hopefully i can get this resolved quickly. this thing runs like a fat old dog.

Very late update but, the car is fixed. The vacuum hoses were routed wrong and the pump was leaking. Replaced both and the jetta was back to beast mode. Thanks everyone for all the help

trueblue88 said:

Very late update but, the car is fixed. The vacuum hoses were routed wrong and the pump was leaking. Replaced both and the jetta was back to beast mode. Thanks everyone for all the help

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I'm curious if the problem started when the hoses were changed or off for some reason.

wonneber said:

I'm curious if the problem started when the hoses were changed or off for some reason.

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I had never touched the hoses since I had bought the car so they had to be misrouted from the start. My dad's mechanic must have moved another hose around to cause it not to boost. I don't know how the car ran like that for such a long time.