Fixed my 4BCC CEL

[bobman21]

Just got this issue and a $3508 quote from the stealership so... 10k Ohm resistor it is.

One question: do you have to pull the actual tank in order to do this? Or can everything be done with the tank installed? Would like to avoid pulling the exhaust and whatnot if I can.

[smuggymba]

Originally Posted by bobman21

Just got this issue and a $3508 quote from the stealership so... 10k Ohm resistor it is.

One question: do you have to pull the actual tank in order to do this? Or can everything be done with the tank installed? Would like to avoid pulling the exhaust and whatnot if I can.

@bobman21 - Did you do this fix already? Can you share some wisdom?

[bobman21]

Yeah, ended up being pretty straightforward, although I'm struggling to remember the details now 30 months later. I've been trouble-free since the fix FTR. Roughly:

1. Underbody panels come off. Tank is located on the driver's side roughly under the driver's seat, maybe a bit farther back where the passenger's feet go.
2. IIRC it has a drain plug. I drained the liquid to save myself on the mess and the weight of unbolting it and pulling it down.
3. The exhaust does not need to come off for this job. It's pretty obvious what you need to do when you get the underbody panels off, although I remember it being mildly annoying (everything went back together without any hassle or needing to mark screws/parts or anything like that).
4. This part I don't remember clearly: how many sensors there are and whether you have to test each one or if it's always the same one that's bad to cause the code. Anyway, there are 2-3 sensors. One at the top of the tank (hence having to remove it to test), one at the bottom, and (maybe) one in the middle. IIRC you take your multimeter and measure the resistance. I think you drain the liquid also so that you can check whether each sensor is offering the right resistance. 10k Ohms is what you want to see. If you don't see 10k Ohms (I believe you just have an open circuit otherwise) then you know the sensor is bad. Again, you'll need to corroborate this with other posts/threads of exactly how to test, this is just a summary of what my (reasonably lazy and inexperienced) approach was and the results.
5. Whichever sensor is bad is the one you bridge. To avoid having a dangling sensor/water intrusion, I took a 10k Ohm resistor and stuffed it into the connector, bridging the two leads of the connector (to be clear: the connector side, not the sensor side. It fits together better that way). This is a tight fit back together because it's not supposed to have a resistor in there... but with enough coaxing it goes back together.
6. Put everything back into its home.

You may be wondering where you get a 10k Ohm resistor. It's not like you can go to a Radio Shack anymore. I happened to have a breadboard kit I bought on Amazon for <$20. But I'm sure you could just buy an assortment of resistors for even cheaper. These are the little guys... the resistor itself is probably 1-2 mm in diameter, and 4-5 mm long. The leads are thin. I just typed "resistor" into Amazon... any of those first hits are fine.

Keep in mind the ECU will now always think the tank is full... so you'll need to be proactive about remembering to fill.

[smuggymba]

Originally Posted by bobman21

Yeah, ended up being pretty straightforward, although I'm struggling to remember the details now 30 months later. I've been trouble-free since the fix FTR. Roughly:

5. Whichever sensor is bad is the one you bridge. To avoid having a dangling sensor/water intrusion, I took a 10k Ohm resistor and stuffed it into the connector, bridging the two leads of the connector (to be clear: the connector side, not the sensor side. It fits together better that way). This is a tight fit back together because it's not supposed to have a resistor in there... but with enough coaxing it goes back together.
6. Put everything back into its home.

Thx a lot Bobman. This really helps me to take up on this job and save 3500.00. Xemodex is also $900 and I'm guessing they do the same.

My main question/clarification is "where to insert the resistor" and in which pins. I saw many threads and it's hard for me to figure out if:

1.) Do I need to use 1 resistor OR 2 resistors?

2.) Does the resistor go from pin1 to pin2?

Adding some pics so you can guide me better; thx a lot!!

[bobman21]

Well that's a pickle... I have no memory of there being 4 pins instead of 2. I suppose if I found myself in your situation right now, I would unplug the other sensors and look for which specific combination of pins (on a working sensor) gives me 10k Ohm. Then just bridge those two pins on the connector for the faulty one.

To answer your question more directly: 1) you only do one bridge (one resistor). 2) Per above, I don't remember. However, in that second photo it does look like it's Pin 1 and Pin 2. The placement of the resistor is just to accommodate routing for the connector to go back. There's no fancy business happening off screen in those folds. I don't think I put my connector back together like that... I think there's multiple ways for the resistor to fit. But it really is just a simple bridge of the two pins. My only question is that it doesn't look like the lead actually hits Pin 1 in that photo. Maybe it's just optics. That's the only reason I think you're safer to test a good sensor to make sure it's the right pins.

[ard]

Re-reading post #1, there are two different tanks, two different sensor fixes...one is a two wire harness, the other is a 4 wire.



Maybe that helps a bit?

[bobman21]

Are you talking about the active tank in the engine bay vs. the passive tank towards the rear? If so, I could be mistaken but I believe this specific code is for the SCR tank in the back.

[smuggymba]

Originally Posted by bobman21

Are you talking about the active tank in the engine bay vs. the passive tank towards the rear? If so, I could be mistaken but I believe this specific code is for the SCR tank in the back.

yes 4BCC is for SCR / Passive Tank (10K Ohm resistor fix)

For Active tank - there's a cheaper VW part that can be used.

[christoepurrr]

Thanks. Recently encountered 4BCC CEL, will reference this guide as a fix.