Fixed my 4BCC CEL

[BigKuma]

“Pull the passive tank” they said, “it will be easy” they said.

I wanted to add more details to what was posted in this thread. Not that it was extremely challenging, but it was time consuming. A couple of hours at least. I wish I was more organized, and created a real guide, but …

1. Remove all the panels under the car on the driver side that live between front and back wheels. You can see part of the tank when you take off one key panel, but it’s best to have them off to avoid breaking expensive and aging pieces of plastic and foam.
2. The tank is immediately forward of the gas tank on the driver side. It is enclosed in two polystyrene foam insulation shells.
3. There is a big black metal brace, with two nuts (13mm). Once removed, the tank will hang on hoses and wires, so figure out how to support it.
4. There are two more 13mm nuts side by side on the side bracket that’s stuck to the tank. It doesn’t slide off the tank, you need to remove the nuts from the car body.
5. Once you can see the big, silver sleeved hose, you will want to pull it off the tank, and drain it or plug it really well. This one has a worm clamp (6mm or 1/4").
6. There are two other hoses that need to be removed. The small one on the bottom has a permanent clamp you’ll have to break and replace later. Top thin hose has a gray button you press before pulling it off.
7. To make things difficult, various wires and hoses are stuck to the tank or brackets holding the tank. Two silver, 90 degree angled brackets can be removed EASILY by turning the metal piece 45 degrees. If you yank and pull, you’ll break off the plastic! Another wire can be removed by squeezing the top of the clip, and sliding it through.
8. There is a small hose in a C shaped clamp stuck to the side plastic corner bracket coming off the tank. Pop it off.
9. You will need to bend or remove part of the heat shield around the exhaust as you remove the tank
10. Once you unhooked everything, slide the bottom clamshell out and set it aside.
11. Pull out the tank, if it’s not moving, some wire or hose is snagged or needs to be disconnected.
12. The top insulating clamshell will stay in the car, as it has a hose that goes up somewhere.

The reason I took it off was to locate a leak and plug it up. But, I didn’t see any leak. I was told by forums that plastic leaks around the sensor and it gets on the wires and that’s why the sensors read wrong. But, my tank looks pretty clean. However, both sensors show 14-18 MEGA Ohms resistance (with and without fluid contacting them). I assume that is “open circuit”. Not sure. But I do get the 4BCC code. I will shove 10k resistors into both circuits. Both sensors have FO1C470061 and 13.06.2012-638-A markings on them.

As the post above pointed out, you don’t need to remove the tanks, you can simply access the harness after removing plastic panels. There was some confusion, but I think I can resolve it with the attached picture. There is a harness that is dedicated to the top and bottom level sensors, it is BOSCH 0280620694. It has a 4 pin connector (you see in other posts) going towards the ECU (black, blue, yellow, brown). Brown and yellow are on a short lead of the Y split, and black and blue are on the long lead. Brown and yellow connect to the bottom sensor, and black and blue connect to the top sensor. You can easily access the two pin connector on the bottom, but the two pin connector on the top requires removing the tank.

The 4 pin connector is plugged into a plug stuck to the metal cross brace. It has a little gray tab you can’t see from the bottom of the car, but you have to slide it out (away from the connection) before attempting to pull it off. That is where you can check impedance and shove resistors if you don’t want to remove the tank.

Hope this helps, feel free to ask questions.

[BigKuma]

I was a little unclear on previous posts, so I wanted to be more thorough in describing the fix.

1. Get a 1/8 W (125mW) 10Kohm resistor. See pictures with measurements. I got the cheapest one from eBay. Most likely, all 1/8W resistors will be about the same size.

2. I used the 4 pin connector for my insertion point. See above post: this is accessible without removing the passive tank. It is where the top sensor and the bottom sensor merge and plug into what looks like a CAN bus transmitter.

3. As you can see, I didn't have to Dremel anything. Resistors, lay flush in the slots that happen to be in the connector plastic already. It just plugged together smooth, but tight. Likely, you'll need to cut off ~1/4 inch of the resistor pins, my final length was 42mm, down from 60mm. Make sure to pre-form the resistor pins slightly as shown.

I reset the codes (make sure to have your car 12V charging, as to not blow up your FRM, like I did). The CEL didn't come back after a few long trips. Not really sure about the passive tank level detection, I didn't refill it after draining. Maybe now ECU permanently assumes tank is 1/2 full (unless it's a pessimist ECU). The resistance range for these sensors is 8K to 12K Ohms.