35d Reducing Agent Passive Tank Sensor Failure

[RADRACR]

Can you elaborate? Where exactly should I look? In the engine bay? Underneath the engine? Photo would be helpful too. I would appreciate it!

[franan]

Do you have a diy picture available thanks.

Originally Posted by johnmn

I pulled the tank out and found that the low level sensor (bottom of tank) had 10k ohms resistance across the leads, but the high level sensor (top of tank) was an open circuit (infinite resistance) across the leads. You want 10 k ohms resistance across the leads of both sensors when the tank is empty.

I spliced/soldered a 10k ohm resistor across the leads of the high level sensor. I then shrink wrapped the resistor and wires, reinstalled the tank, and the check engine light turned off. That was 5 months ago - still no issue.

You could probably do the same thing without removing the tank as the leads to both sensors are accessible and visible at the bottom of the tank.

Definitely worth it to avoid paying the $1300+ for a new tank!

[RADRACR]

Following up. Would be helpful if you could shed some more details. Thanks John!

[johnmn]

Sorry, I didn't take a lot of pictures, but I'll share what I have and hand-wave through the rest.

The passive tank is under the vehicle approximately under the drivers seat:



Remove the two plastic shields covering the tank that are held on with an array of fasteners. Once exposed, the tank will have a black foam cover on it.



Drain the tank if you want to remove it. You'll need to cut off the hose clamp.



Then remove the bolts in the brackets holding the tank to the vehicle. You'll also have to disconnect the sensor and hoses connected to the tank.

Once removed, the tank looks like this...

Top:



Bottom:



Next splice a 10k OHM resistor in the wire shown:



To splice in the resistor I unwrapped the tape around the wires and cut one wire then the other about 1.5 inches away from the first. This was to prevent a short circuit. I then slid a piece of heat shrink tubing on the wire to seal the assembly later. Next I stripped and reattached the wires with an end of the resistor in each of the spliced wires, then soldered the resistor in place. I then slid the heat shrink tubing over my splice and sealed the repair. Sorry, no photos of that, but I have this crude sketch of it:



Reassemble the tank into the vehicle and install a new hose clamp to replace the one you cut off.

Refill the tank. When you start the vehicle you'll hear the def tank pump run a long time as it fills the active tank. It seemed line mine ran for 10 minutes or more, but it will eventually shut off.

Now enjoy CEL free (assuming you don't have other codes) driving!

[RADRACR]

Awesome write-up! Will be diving into this shortly. Thanks!

[franan]

Excellent thank you.

Originally Posted by RADRACR

Awesome write-up! Will be diving into this shortly. Thanks!

[Ozer]

This affects anything for those of us in the colder climate? Anyone know?
My cell comes on now that its winter, all summer i was fine but colder months the cell visits, just like Santa

[RADRACR]

Originally Posted by Ozer

This affects anything for those of us in the colder climate? Anyone know?
My cell comes on now that its winter, all summer i was fine but colder months the cell visits, just like Santa

I've had the vehicle for 2 years in Miami and this is the first I've seen of it. The vehicle spent time up north before that.

[markehz]

Originally Posted by Ozer

This affects anything for those of us in the colder climate? Anyone know?
My cell comes on now that its winter, all summer i was fine but colder months the cell visits, just like Santa

Interesting that you point this out.
My previous "Low DEF" warning was last spring and the CEL didn't come on at all. This time, it came on at almost the same time as the "Low DEF" warning.

Anyone else in the cold zone having this issue?

[Ozer]

Originally Posted by markehz

Interesting that you point this out.
My previous "Low DEF" warning was last spring and the CEL didn't come on at all. This time, it came on at almost the same time as the "Low DEF" warning.

Anyone else in the cold zone having this issue?

My Low DEF came on and the heater element code at the same time.
I put 2.5gl into the passive tank then few weeks later when i got the BMW bottle i also put that in. Few days later my light went off and its been a week, no stored codes or anything. Knock on wood.