[QUIKDZL]

I'm getting a SERVICE ENGINE SOON light because of Codes 0046F9 and 004D32 (reducing agent active temperature sensor has failed - open circuit). From my research, it seems that this active tank temperature sensor notifies the ECU when the temperature of the urea is at or below 25F, which has probably never happened for this car. At these cold conditions, a line heater and/or a reservoir heater are activated to prevent urea freezing.

It seems that this temperature sensor is integral to the tank (genius), so in order to replace a $10 RTD, my dealer wants over $2000 to replace the entire tank. I'm thinking that a good workaround would be to install an RTD on the outside of the tank, bypassing the failed one.

Can anyone tell me what two wires to hijack, and where to find them? Any better ideas?

[glitdi]

Before you go hacking stuff up, may I suggest testing the sensor, most temp sensors are very simple two wires and are built of a bi metal strip.
Problem with dealerships is they don't spend the time to diagnose any more they plug in their lab scope follow prompts and chuck parts at things, proper diagnosis is expensive or so they think they prefer to throw parts at shit...( we have all seen perfectly good injectors throw at our cars due to cbu issues) Run an ohmmeter across the two terminals and see if there is any type of resistance, if there is any type of resistance than its a wiring issue which is more likely the cause. I doubt they would use a 3 wire (canbus) temp sensor and besides temp sensors are pretty reliable. If someone has a wiring diagram I can have a look and verify where to test etc.. Its improbable that its a sensor issue not impossible, before throwing parts at it maybe check it out a little especially being an open.
Other things to think about, I am not a 335d expert but urea freezes at about -10 degrees fahrenheit or 14 celsius thus the reason for the sensor. Most addblue system pumps the add blue from the nozzle to the tank every time you turn off the car due to the sensitivity to freezing. Any lines that have addblue in them could potentially fail and freeze. if you were to add a resistor to cheat the system the car would not know the true temperature of the urea figuring out a nice medium for a resistance would be a little difficult and the problem is is on a cold day the add blue could be in solid frozen state and if the car thinks the add blue is liquid it could prematurely cause your add blue pump to fail. Just a thought...hope this helps

[Abax335]

Originally Posted by glitdi

Before you go hacking stuff up, may I suggest testing the sensor, most temp sensors are very simple two wires and are built of a bi metal strip.
Problem with dealerships is they don't spend the time to diagnose any more they plug in their lab scope follow prompts and chuck parts at things, proper diagnosis is expensive or so they think they prefer to throw parts at shit...( we have all seen perfectly good injectors throw at our cars due to cbu issues) Run an ohmmeter across the two terminals and see if there is any type of resistance, if there is any type of resistance than its a wiring issue which is more likely the cause. I doubt they would use a 3 wire (canbus) temp sensor and besides temp sensors are pretty reliable. If someone has a wiring diagram I can have a look and verify where to test etc.. Its improbable that its a sensor issue not impossible, before throwing parts at it maybe check it out a little especially being an open.

We have had a few of these were guys shotgunned tanks in and end up finding out it was a combination of a bad harness (excess resistance) and loose pins. So we put new connectors on the sensor side and replaced the harness.

[Yozh]

Correction: urea freezes at -11celsius or 12Fahrenheit.

[QUIKDZL]

Thanks for your replies. I'm not interested in hacking anything up. This sensor is not accessible--it is integrated into the tank. If it is not a dirty connector or broken wire, I would prefer abandoning the tank sensor and adding an external temperature sensor, discreetly attached to the outside of the tank. This way, I would not lose any functionality and the annoying light would go away.

I'm in South Carolina, so my urea will never freeze. I'd rather find some way to eliminate the light than spend $2000 to repair a feature that I'll never use.

If Abax or someone could tell me where to locate the harness and which wires/pins to focus on, I'd be happy to check/clean connections, measure resistance, etc. If the problem actually is a bad/open sensor, I would then know which wires to cut and install a remote RTD. Anyone have this information?

[Abax335]

Originally Posted by QUIKDZL

Thanks for your replies. I'm not interested in hacking anything up. This sensor is not accessible--it is integrated into the tank. If it is not a dirty connector or broken wire, I would prefer abandoning the tank sensor and adding an external temperature sensor, discreetly attached to the outside of the tank. This way, I would not lose any functionality and the annoying light would go away.

I'm in South Carolina, so my urea will never freeze. I'd rather find some way to eliminate the light than spend $2000 to repair a feature that I'll never use.

If Abax or someone could tell me where to locate the harness and which wires/pins to focus on, I'd be happy to check/clean connections, measure resistance, etc. If the problem actually is a bad/open sensor, I would then know which wires to cut and install a remote RTD. Anyone have this information?

PM me a vin I'll get you a wiring diagram if you want to get crazy.

Unplugging the sensor is going to be a pain since its at the top of the tank. Requires the exahust to be removed or hung, unless you snip the harness at the body side and put said resister inline further up the system.

Only thing I would be worried about is plausability faults that may come up with ambient air temp

[bagman]

I replaced the DEF temp sensor in my car with a water temp sensor from a mid 90s voyager minivan. The temp/resistance profile is about the same for both. I just left it tie wrapped to the harness on top of the tank so it's measuring air temp around the tank, not actual DEF temp. The trunk floor needs to be removed. That's been covered somewhere on this forum. There are two 4 wire bundles going into the tank. One bundle has wires all the same size and they are for level sensing. The other bundle has 2 large and 2 small wires. The large go to the heater and the small to the temp sensor. I live in NY state and we have been having a real mild winter so I don't know yet how things are going to work when it gets down to zero. My hack has been in for about 6 months without a code.

[Nadir Point]

Originally Posted by Abax335

PM me a vin I'll get you a wiring diagram if you want to get crazy.

Or you can go here and browse about yourself if you like:

[QUIKDZL]

PM sent.

[QUIKDZL]

Originally Posted by bagman

I replaced the DEF temp sensor in my car with a water temp sensor from a mid 90s voyager minivan. The temp/resistance profile is about the same for both. I just left it tie wrapped to the harness on top of the tank so it's measuring air temp around the tank, not actual DEF temp. The trunk floor needs to be removed. That's been covered somewhere on this forum. There are two 4 wire bundles going into the tank. One bundle has wires all the same size and they are for level sensing. The other bundle has 2 large and 2 small wires. The large go to the heater and the small to the temp sensor. I live in NY state and we have been having a real mild winter so I don't know yet how things are going to work when it gets down to zero. My hack has been in for about 6 months without a code.

Sounds perfect, bagman. More details? You have a part number for that sensor?

[bagman]

Reduction Tank Temperature Sensor GM 2015
°C °F OHMS
Resistance Values are ± 3%
Temperature Values are ± 5%
−5 23 42,315
0 32 32,650
5 41 25,388
10 50 19,900
15 59 15,708
20 68 12,490
25 77 10,000
30 86 8.057
35 95 6,531
40 104 5,327
I got mine from a junk yard and took a cheap ohm meter with me to measure resistance. It was about 60 that day so I was looking for a resistance of around 15,000 ohms. The part came out of a mid 90s voyager v6.

[QUIKDZL]

UDAMAN. I can't locate that part number, though, and I don't think Chrysler produced any diesel minivans, so what part/application should I be looking for?

[bagman]

Your not looking for a diesel. Your looking for a water temperature sensor for a gasoline powered V6 voyager along with the electrical connector that plugs into it and a few inches of wire. The sensor is on the top, front of the engine.

[Yozh]

To the OP. You may wish to do a full flush of your Urea tank. The tramperature sensor is inside the function unit in the active tank and if you are in a hotter climate, urea crystallizes quite quick. It is possible that the temperature sensor just has a bit of build-up on it. Definitely do test it before you go cutting any wires.

Tanks are mounted from below to the metal plate that you see when you pop the trunk floor up. Item 23 here:



But to get to the two nuts you need to remove the heat shields. I know a few can chime in, but I do not think you can easily remove the heat shields without at least partially disconnecting the rear section of the exhaust. If you unhook the urea tanks you need to support them then. There is also a small bracket that is connected at the front passenger side to the trunk plate, you need to unscrew that. What I am getting at is, you can get to all the connectors up at the top without removing the tanks fully. And yes, you can get to the inside of the function unit by disconnecting and removing the white delivery unit. May be just cleaning everything and make sure all the electrical connectors are good is all you need. Here are a few of my pictures, a wiring diagram and some general info. Hope that helps.














335d Wiring 2 of 7.pdf

[QUIKDZL]

Wow, Yozh, that's a BIG help. Many thanks! My codes are indicating an open temperature sensor, but it has corrected itself twice on its own. So I have a loose/dirty connector or broken wire to the RTD. Hopefully, I can find a smoking gun at the connection, but I have a handfull of RTDs so I can install a new one if necessary. Now it appears that I can even install one inside the active tank function unit!

Do you know which connector/wire pair are for the temperature sensor?

[QUIKDZL]

BTW, why can't BMW sell me this function unit as opposed to the entire urea tank???

[Nadir Point]

Originally Posted by QUIKDZL

BTW, why can't BMW sell me this function unit as opposed to the entire urea tank???

Same reason you have to buy a $300 assembly with 2 couplers, bend and the pipe if you just want any single piece that connects the intercooler to the EGR valve.

[HeatherM35d]

Here's a nice view of the low pressure egr system, egr cooler and dpf

[335dlci]

Originally Posted by HeatherM35d

Here's a nice view of the low pressure egr system, egr cooler and dpf

This setup is only on x5 though. I have never removed a x5 DPF. Does it weigh more than a 3?

[HeatherM35d]

Originally Posted by 335dlci

This setup is only on x5 though. I have never removed a x5 DPF. Does it weigh more than a 3?

Dpf is the same, the 3 series doesn't have the low pressure egr. X5 has both high pressure like 3 series and low pressure system, which is pictured above.

Post edit: dpf canister is the same size

[davegris]

Yozh, it looks like you disassembled and cleaned your tank? True? If so did you have any luck with the codes clearing?

I have the same code for short circuit on the temperature sensor and suspect it may be due to crystallation. I've been thinking about trying your exact suggestion on the full flush.

[Yozh]

Originally Posted by davegris

Yozh, it looks like you disassembled and cleaned your tank? True? If so did you have any luck with the codes clearing?

I have the same code for short circuit on the temperature sensor and suspect it may be due to crystallation. I've been thinking about trying your exact suggestion on the full flush.

I would not call "disassemble" what I did. Tank is not exactly disassembleable, but I was curious if I could get inside the function unit, and looks like one can. I did not have any urea related codes at the time. Had full deletes done a while ago and just wanted to yank the tank out of the car to get rid of the dead weight. But I can see how dirt/urea crystallization of urea can cause some potential issues. This is how mine looked: