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We've had a number of these tanks with bad sending units come through the shop. They won't give a low signal and then when we fill the tank back up they still show low.
If you still have warranty it should be covered, but if not you will have to replace the DEF sending unit assembly.
Would you like diagrams that show you where to start as far as testing the signals and probably replacing it?
To diagnose this one you will need a milti-meter and a scan tool that can read the DEF level PID:
With connectors unhooked, check continuity of each wire for no opens in harness. The wires are: a) RDL1 - Pin 6 (Yellow/Grey) at tank to RDL1 - Pin 15 at TCM. b) RDL2 - Pin 7 (White/Brown) at tank to RDL2 - Pin 18 at TCM. c) RDL3 - Pin 8 (Violet/ Grey) at tank to RDL3 - Pin 19 at TCM. d) RDLRTN - Pin 5 (Green/Violet) at tank to RDLRTN - Pin 32 at the TCM.If wiring is intact, check each for being shorted to voltage and repair as needed. If OK, check for a pulsing voltage on the signal wires with both connectors connected.If the wiring checks good, disconnect connector C3616 again. With key off, jump pins 6, 7 and 8 to pin #5. Turn the key on and access the REDUCT_TNK_LV (PER) PID in Data. If the PID reads 100% with pins jumped, install a new Reductant Heater and Sender assembly.
Here is the PIN out diagram.
Please let me know if you need any additional information.
I just wanted to see if you need more help. Please don't forget to rate.