CDI water sensor - Mercedes-Benz Forum
 
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post #1 of 8 (permalink) Old 10-09-2018, 08:48 AM Thread Starter
ot1
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Question CDI water sensor

2006 E320 CDI . I suspect water in my fuel. There is a water sensor in the filter, however unplugging the sensor connector brings up nothing on the display, lights no warning... no indication thats its even working.

How is it tested?
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post #2 of 8 (permalink) Old 10-13-2018, 05:13 AM
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I am surprised that none of the diesel experts responded yet. Although this does not answer your question, here is one page I found while doing a search:

https://www.google.com/search?q=merc...nt=firefox-b-1

Here is another search which may provide more answers to your question:

https://www.google.com/search?q=how+...nt=firefox-b-1

Mike T.
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post #3 of 8 (permalink) Old 10-20-2018, 06:59 PM Thread Starter
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Originally Posted by mtrevelino View Post
I am surprised that none of the diesel experts responded yet. Although this does not answer your question, here is one page I found while doing a search:

https://www.google.com/search?q=merc...nt=firefox-b-1

Here is another search which may provide more answers to your question:

https://www.google.com/search?q=how+...nt=firefox-b-1

Mike T.
Thanks for the links but they provided nothing useful.
I think might buy a sensor for $100 and test it in cup of water with the engine running and of course the old one still fitted to the filter.

Maybe...
Obviously the sensor is not tested when the vehicle is started since no warnings were displayed when I had it unplugged. I will check it again but I let the vehicle run for twenty minutes with it unplugged.
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post #4 of 8 (permalink) Old 12-22-2018, 05:03 PM Thread Starter
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Originally Posted by ot1 View Post
Thanks for the links but they provided nothing useful.
I think might buy a sensor for $100 and test it in cup of water with the engine running and of course the old one still fitted to the filter.

Maybe...
Obviously the sensor is not tested when the vehicle is started since no warnings were displayed when I had it unplugged. I will check it again but I let the vehicle run for twenty minutes with it unplugged.
I ended up buying a new water in fuel sensor, and tested it in a small cup of water. The old sensor was original, they are date stamped, and it was tested and worked. I didnt have any means to test the old one until I bought a new one.
No coverage in the owners manual.
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post #5 of 8 (permalink) Old 12-26-2018, 05:45 AM
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Water sensor is a normally open contact. So disconnecting the sensor will not change the state of the contact. It will remain an open contact.
When the contact is introduced to water the conductivity of the water completes the circuit. Which allows signal voltage back to the computer.
The only way to tell if a water sensor is still working is to dip it in water and see if the circuit is completed. Can be done on a bench using an ohm meter. Can also be done plugged into the cars computer.
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post #6 of 8 (permalink) Old 12-26-2018, 02:34 PM Thread Starter
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Originally Posted by Bobatsea View Post
Water sensor is a normally open contact. So disconnecting the sensor will not change the state of the contact. It will remain an open contact.
When the contact is introduced to water the conductivity of the water completes the circuit. Which allows signal voltage back to the computer.
The only way to tell if a water sensor is still working is to dip it in water and see if the circuit is completed. Can be done on a bench using an ohm meter. Can also be done plugged into the cars computer.
Yes I realized it was an a normally open circuit after I purchased a new sensor, not knowing if the original one was defective or not. However it should have been designed as a closed circuit sensor, so that leaving it unpluged or the sensing of water would trigger a dash warning. This connector gets unplugged everytime the fuel filter is changed, therefore it is susceptable to accidentally leaving it unplugged. Its a critical sensor, not just for grins. Testing it on the bench could be an option but in risk of damaging the sensor not knowing how it works and it not a simple matter of hooking it up to and ohm meter since its a powered sensor not just 2 leads, it is a 3 lead design and then one needs a bench in a garage out of the weather. For me its far easier to test it in vehicle as I did. This post was created 3 months ago and no one offered any revelations, absolutely nothing is in the owners manual NOR IS ANYTHING IN WIS, about its function or testing so I decided to analyze the sensor’s working on my own by immersing it in a cup of water as explained and photo attachment.

Last edited by ot1; 12-26-2018 at 02:38 PM.
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post #7 of 8 (permalink) Old 12-28-2018, 09:26 AM
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We appreciate your research and sharing the experience
I am driving diesels in CA and NV for well over 25 years and had few big engines with glass water separators.
In all those years I never found water in fuel, when I know that whole USA replaced single wall tanks at gas stations with double walls in last 10+ years, what suppose to solve condensation issues those tanks had in the past.
In the meantime I had situation with gasoline, when somehow couple CUPS of rusty water ended in my tank. That was before stations tanks replacement.
So per my experience water in fuel is not likely going to happen. Maybe that's why MB did not made drain valves on filters, like my diesel Fords, Caterpillars and Detroit had.
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post #8 of 8 (permalink) Old 12-29-2018, 06:50 PM Thread Starter
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Last time I remember In illinois, two years ago my e350 van with a 7.3L, the water in fuel lite came on, but maybe you know, easy to pull the drain valve, fixed the problem in 2 minutes. That drain is also great to use for priming, just crank it over with the valve open. Over the years maybe happened 10 times. Holds 42 gallons.
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