Volkswagen Passat Forum banner

AFN Fuel pump still under voltage

5747 Views 2 Replies 3 Participants Last post by  FrescoGreen01.5
Hello all,
my english is not very good, so please be patient:) I really need your help.

One day i came to my car (Passat B5 AFN 1998) and battery was dead. Then after charging i checked consuption, which was 2,5A (key was not in ignition). There was one more strange thing - wierd sound from rotary fuel pump when i was connectiong battery.
Here you can see it:
Both connectors of fuel pump did some sound, after disconnecting both of them, consumption dropped to 0,5A.

VAG-COM said:
01266 - Glow Plug Relay (J52)
31-10 - Short to Ground - Intermittent
00626 - The preheating time (K29)
31-10 - Short to Ground - Intermittent
17978 - Engine control unit blocked
P1570 - 35-00 -
01117 - Signal load for the alternator terminal DF
27-00 - senseless signal
00668 - Onboard voltage sv.30
27-10 - senseless Signal - Intermittent
00765 - Proximity sensors regulatory latches (G149)
35-00 -
01268 - Quantity control (N146)
35-00 -
01268 - Quantity control (N146)
27-00 - senseless signal
(sorry for the translation, i have czech VAG-COM)

The problem is, that fuel pump is still under voltage.. I tried to connect other fuel pump - same sounds - so probem is not in the pump.
So i tried checking wiring, some friends told me, there may be water/oxidation in the box, where engine control unit is. I checked it, but it seemed to be okey... Anyway i tried to unplug everything possible while i was reconnecting the battery and listeng to the pump.

There in box are 5 connectors to interior wiring... One of them - orange has i think 5 wires (except one of them, all are 12V). I Assume, it is correct.. But i am not sure.
I unplugged also all three relays which are in that box. Only that orange conector and control unit stayed connected and fuel pump was under voltage..
My deduction: Problem is in the orange connector(interior wiring leading to that connecotor), or in control unit, or somewhere else in the engine wiring.

Is it possible there is problem in control unit? Or is there any other critical place in the engine wiring, which should be checked?

I would appreciate any advice, thank you.
See less See more
1 - 3 of 3 Posts
A switch or relay electrically connected to the pump may be "shorted". With the battery connected, remove one-by-one fuses from the fuse panel until the pump stops. You'll now have to trace and inspect that electrical circuit.
VW did not sell a diesel Passat in the US until 2004 (I think), so my Bentley book doesn't cover your exact car. That may be why there so few posts, too.

But your problem is probably a faulty relay. Our cars all use a relay to switch power to the fuel pump. That relay, and many others, are on the relay panels beside the driver's left foot... In other words, just under the fuse box, but accessed from inside the car. You have to remove 2 bolts to remove the plastic trim piece to get to the relay panels.

The fuel pump relay is on the primary 13-position relay panel. (There is an auxiliary 13-position relay panel and an 8-position panel, too.) The positions are numbered (in the book) from left to right, top row then bottom row, so position 1 is top-left, position 7 bottom-left, etc.

The relays also have "production" numbers stamped on them. In gasoline engine Passats, the fuel pump relay production number is 208, and it is in position 4 on the primary 13-position relay panel. In the 2005 Diesel model, the fuel pump relay is in position 10; your car is older, so it might be different, but that should get you close. Don't depend on the production number to be correct--someone else may have replaced or moved relays.

In all the schematics I looked at, the fuel pump relay switches power to fuse 28 (on the main fuse panel, accessible with the driver's door open). You can check for voltage at fuse 28 to see if the relay is working, or to see when you have identified the correct relay. The relay should have just 4 contacts (blades). There is another relay (power control relay) in the 2005 design that switches power to much of the engine control, including the fuel pump, but it has 5 contacts (blades). It is in position 3 on the relay panel.

The negative side of the relay coil is switched to ground by the ECM to turn the fuel pump on, but I doubt the ECM is the problem. The ECM seems to be a very robust design.

Until you get this problem fixed, you can remove fuse 28 to stop the fuel pump from draining your battery--that's much easier than disconnecting the battery.

Hopefully you just need a new relay! Good luck.
See less See more
1 - 3 of 3 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.