Fuel Pump Relay

Where is it? I'm not coming up with anything and I need to stop the lift pump from running so I can run a can of diesel purge through it. This is for a 2012 Passat SEL.

Best to unplug the battery. My JSW just had its relay failure twice in a week. Obviously in-tank or aux pump killing it. So you are better off unplugging it. The most easiest way to do it.


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calimustang said:

Best to unplug the battery. My JSW just had its relay failure twice in a week. Obviously in-tank or aux pump killing it. So you are better off unplugging it. The most easiest way to do it.


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Unplugging the battery does me no good. I need the location of the relay or fuse so I can pull it and run the car without the lift pump running.

Here's a note. Don't freaking waste your money trying to run a can of diesel purge through an NMS passat properly. It won't even start if you unplug the in tank lift pump at the tank, and I could not find anywhere that would identify the fuel pump relay, and I have my reservations if one was properly found that the car would attempt to run anyway. Dumped the $10 bottle of crap in the tank and cut my losses.

diesel purge? what is this 1984? IMO ULSD took care of a ton of issues that diesel purge was needed. If anything toss the can or two in the tank with under 1/4 tank, drive it for 100 miles then fill up. That or just run power service does every other tank.

I've stopped running additives except PS white on the transition periods in the fall, but I've kinda forget.

749GLE, so you are recommending not to use liqu moly fuel additive?


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I think it had it's time and place in older diesel technology. I remember my grandfather running diesel purge on his '77 300D and you could hear the engine changing as it "cleared things" up.

As for being a must to get these cars to 300K, it hasn't been proven, but again is a cheap insurance that may let you sleep better.

I probably spent a good $150-200 on diesel additives over the miles, are my car betters off for that, well one got crushed at 140K, the other got sold back to VW with 80K, and the other has about 26K. All of them have been trouble free for major issues.

I'd much rather stick to good fuel sources than strict additive regiments.

My '13 is at 238k and never had 1 drop of additive, but I have also used fuel that is labeled as "up to 5% Bio-diesel" about 95% of the time. No clue as to the "real" amount of Bio that is in the fuel, if any at all.

To answer your question, just plumb the supply between the filter and the engine back to the return to the tank. It worked fine on my BRM engine. As far as the car knows, it's still running off of fuel supplied by the tank.

Is doing a Diesel Purge worth it? I do have an opinion but won't even comment because that is not what you asked. I just hate it when people don't know the answer to a question and instead offer up their opinion as some sort of Holy Grail.

Well, FWIW I was going to run the can of diesel purge because I what what I believe to an injector (or multiples) giving me some trouble, and I wanted to clean things out before it gets cold when the issues rears it's head again. Just as a "see what it does" measure. I had HORRIBLE random engine cold knocking issues last year, and my fuel economy this year is significantly off (haven't gone over 700 miles on a tank all year, usually got 720ish with my normal commute in spring/summer/fall wx).

Well report back if you think direct tank dosage improved the injector issues.

AFAIK, the control system for fueling/injecting is pretty sensitive, if there is an error it'd toss a CEL, but I could be wrong.


You have the EPA fix yet? that may pin point the MPG decline.

EPA fix was done in June of 2017. Later that summer I was getting 50MPG, literally, on the highway.

The hard knocking when cold started last winter. Car hasn't sounded the same since that started, and fuel economy was down 3-4 MPG since. I did do new tires late last winter also, which I tentatively can attribute to some of the loss.

So this is the first full tank being run since doing an oil change, DSG service, and timing belt job during last week. Currently have 220 miles on the tank and I'm shocked to report that it's telling me 510 to empty still......so around 730 on the tank with my normal driving. I haven't seen that all year. Did the diesel purge help? Can't specifically say given the other work that was performed. But it's running quieter than recent months, and seems to have recovered quite a bit of the economy I lost. I'd have preferred to have run the stuff direct into the injection system just to clean it out as best as possible, but given the cumulative results so far, I'll take it.