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DEF P205B temp sensor DIY fix

65K views 15 replies 11 participants last post by  candyhughes62 
#1 · (Edited)
Just wanted to post a DIY fix for the dreaded adblue tank temp sensor. Before posting I wanted to insure it would work. I've been running it for about six months now with no issues. This is only for the temp sensor failure and not the heaters or pump. Some may get other codes if the temp sensor fails during colder months, so you need to insure that it's just the temp sensor. Easy way to do this is clear all codes and when the CEL comes on check codes to see if it's just P205B.

You will need a 10k thermistor which can be purchased off eBay for $1.99-$10.00 depending on quality. Make sure it is H20 proof. You can find these labeled as aquarium tank temp sensors, but must be a 10k ohm.

First you need to remove the tank. Find the connector attached to the fill neck. This is where you are going to connect the new sensor. The small black and white wires on the bottom are the temp sensors. These are the two wires to connect the new sensor too. Make sure you cut them on the sensor side black and white and not the other side of the connector. This will allow plug and play if you ever have to replace the whole unit. Make sure you cover/seal the bare wires from the old sensor as to reduce creep down the wires into the tank.
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I drilled a hole into the fill cap as this was a trial fix and the cap is a lot cheaper to replace than the whole tank. Run the new sensor through the hole and make sure you have enough wire to reach the bottom of the tank. Make sure that if you use this method that you seal the hole with silicone to prevent leakage through splashing. You can use your own method for getting the sensor in the tank, but remember some day the pump or heater may go out and you will have to replace the whole unit, so then you could replace the fill cap and it'll be like new.

I did have to replace the sensor once because when I first did this I used a used one from a fermentation temp controller I had. Below are some photos of the fix.
 
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#6 ·
Just wanted to post a DIY fix for the dreaded adblue tank temp sensor. Before posting I wanted to insure it would work. I've been running it for about six months now with no issues. This is only for the temp sensor failure and not the heaters or pump. Some may get other codes if the temp sensor fails during colder months, so you need to insure that it's just the temp sensor. Easy way to do this is clear all codes and when the CEL comes on check codes to see if it's just P205B.

You will need a 10k thermistor which can be purchased off eBay for $1.99-$10.00 depending on quality. Make sure it is H20 proof. You can find these labeled as aquarium tank temp sensors, but must be a 10k ohm.

First you need to remove the tank. Find the connector attached to the fill neck. This is where you are going to connect the new sensor. The small black and white wires on the bottom are the temp sensors. These are the two wires to connect the new sensor too. Make sure you cut them on the sensor side black and white and not the other side of the connector. This will allow plug and play if you ever have to replace the whole unit. Make sure you cover/seal the bare wires from the old sensor as to reduce creep down the wires into the tank.
View attachment 4645 View attachment 4646 View attachment 4647 View attachment 4648 View attachment 4649 View attachment 4650
I drilled a hole into the fill cap as this was a trial fix and the cap is a lot cheaper to replace than the whole tank. Run the new sensor through the hole and make sure you have enough wire to reach the bottom of the tank. Make sure that if you use this method that you seal the hole with silicone to prevent leakage through splashing. You can use your own method for getting the sensor in the tank, but remember some day the pump or heater may go out and you will have to replace the whole unit, so then you could replace the fill cap and it'll be like new.

I did have to replace the sensor once because when I first did this I used a used one from a fermentation temp controller I had. Below are some photos of the fix.
I've just joined up to say thanks for this post. I've just finished putting a temperature sensor in and have got rid of the little orange light! I ran my sensor through a hole in rhe filler neck that I made with a soldering iron and sealed with a hot glue gun. Time will tell how it lasts but at least I won't have to clear error codes every trip.
 
#7 · (Edited by Moderator)
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VAG Error Code: 9688

EOBD II Error Code: P205B

Fault Location:
Reductant Temperature Sensor - Circuit Range/Performance Problem/Implausible Signal

Possible Cause:
Malfunction Indicator Lamp (MIL)(K83) active.

Wiring/Connector(s).
Reductant Temperature Sensor.

Possible Solutions:
Check/Replace all faulty Wiring/Connector(s).
Read Measuring Value Blocks (MVB).
P205B temp sensor DIY fix.

As taken from my new Free EOBD II Error Codes software
 
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#8 ·
Just wanted to post a DIY fix for the dreaded adblue tank temp sensor. Before posting I wanted to insure it would work. I've been running it for about six months now with no issues. This is only for the temp sensor failure and not the heaters or pump. Some may get other codes if the temp sensor fails during colder months, so you need to insure that it's just the temp sensor. Easy way to do this is clear all codes and when the CEL comes on check codes to see if it's just P205B.

You will need a 10k thermistor which can be purchased off eBay for $1.99-$10.00 depending on quality. Make sure it is H20 proof. You can find these labeled as aquarium tank temp sensors, but must be a 10k ohm.

First you need to remove the tank. Find the connector attached to the fill neck. This is where you are going to connect the new sensor. The small black and white wires on the bottom are the temp sensors. These are the two wires to connect the new sensor too. Make sure you cut them on the sensor side black and white and not the other side of the connector. This will allow plug and play if you ever have to replace the whole unit. Make sure you cover/seal the bare wires from the old sensor as to reduce creep down the wires into the tank.
View attachment 4645 View attachment 4646 View attachment 4647 View attachment 4648 View attachment 4649 View attachment 4650
I drilled a hole into the fill cap as this was a trial fix and the cap is a lot cheaper to replace than the whole tank. Run the new sensor through the hole and make sure you have enough wire to reach the bottom of the tank. Make sure that if you use this method that you seal the hole with silicone to prevent leakage through splashing. You can use your own method for getting the sensor in the tank, but remember some day the pump or heater may go out and you will have to replace the whole unit, so then you could replace the fill cap and it'll be like new.

I did have to replace the sensor once because when I first did this I used a used one from a fermentation temp controller I had. Below are some photos of the fix.
Hello
Can you tell me which type of thermistor did you buy, i understood that is 10k , but the type that it lower the rezistance when the temperature is cold, or the rezistance is higher when the temperature is cold. Or can you post the link with the termistor that u buyed please.
 
#10 ·
I did this fix back in Janurary when I needed the CEL to go off for emissions. It worked great. 10,000ish miles later I forgot to add DEF to the car. The car did not have any indicators of low DEF like it usually does. So essentially the car did not start until I added DEF which was a big relief. So with that being said, has anyone had the same issue with this fix making the computer think that the level is high enough to prevent the automatic countdown?
 
#11 ·
Just wanted to post a DIY fix for the dreaded adblue tank temp sensor. Before posting I wanted to insure it would work. I've been running it for about six months now with no issues. This is only for the temp sensor failure and not the heaters or pump. Some may get other codes if the temp sensor fails during colder months, so you need to insure that it's just the temp sensor. Easy way to do this is clear all codes and when the CEL comes on check codes to see if it's just P205B.

You will need a 10k thermistor which can be purchased off eBay for $1.99-$10.00 depending on quality. Make sure it is H20 proof. You can find these labeled as aquarium tank temp sensors, but must be a 10k ohm.

First you need to remove the tank. Find the connector attached to the fill neck. This is where you are going to connect the new sensor. The small black and white wires on the bottom are the temp sensors. These are the two wires to connect the new sensor too. Make sure you cut them on the sensor side black and white and not the other side of the connector. This will allow plug and play if you ever have to replace the whole unit. Make sure you cover/seal the bare wires from the old sensor as to reduce creep down the wires into the tank.
View attachment 4645 View attachment 4646 View attachment 4647 View attachment 4648 View attachment 4649 View attachment 4650
I drilled a hole into the fill cap as this was a trial fix and the cap is a lot cheaper to replace than the whole tank. Run the new sensor through the hole and make sure you have enough wire to reach the bottom of the tank. Make sure that if you use this method that you seal the hole with silicone to prevent leakage through splashing. You can use your own method for getting the sensor in the tank, but remember some day the pump or heater may go out and you will have to replace the whole unit, so then you could replace the fill cap and it'll be like new.

I did have to replace the sensor once because when I first did this I used a used one from a fermentation temp controller I had. Below are some photos of the fix.
Do the other 2 wires stay connected? Do you remove the old sensor completely? Picture sort of hard to see.
 
#12 ·
Hello all. I have a 14 Passat SEL TDI and just had this code come on. I was curious if someone could shed some light on how big of a problem this is to drive with? I have to leave in a week to drive 1800 miles for work and want to know if it is safe for the car to do so if I can't get to the fix before then? Thanks.
 
#14 · (Edited)
Can I just put a 5k resister and leave it outside the tank. Living in Florida, the heater should never turn on, right?

edit: actually I read somewhere the 10kohm resistor is equivalent to 25*C or 77*F.

I bought a 10kOhm thermistor. It measured 10.3kOhm at room temperature (72*F) and something like 6kOhm at 98*F.
So, as the temperature rises the resistance lowers. An NTC. I will let you know if it works.
 
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