[roachmmflhyr]

Looks like a typical low volt (usually +5vdc) sensor, should see 3 wires coming from that gauge: ground: pin 6 +VDC: pin 13 Signal: pin 14 To test, check voltage between pins 6 and 13, see what that is if its 12 or 5 or 3 or whatever it is. Next test, check between 6 and 14 using volt setting on multimeter, noting the level of your tank at full. Test again when tank is completely empty, those are your two set points and should be relatively linear. Now comes the fun part! Assuming everything above is exactly as I described, you'll see a specific voltage when it hits empty. Let's say that is 1 volt, and 5 volts is a full tank. You can then use a switch to flip between the sensor and a 5 volt output, basically taken from pin 13, that would fool the system into thinking its now full. I'd also use a center off spdt switch. Why? So that the switch doesn't short the sensor and the reference voltage for a split second.

Thanks for the very informative post. Good work! Do you know if these electrical schematics are available for a 2016 LML?

 

[roachmmflhyr]

Sorry, I don't know if they are available for the '16, you can try searching the GM upfitter website to see if they have your year in there though.

https://www.gmupfitter.com/wp-content/uploads/2021/06/2018_Elec_BPrac_093017.pdf

I found the same body builder manual for my 2016 LML but unfortunately it doesn’t have any pin out for the DEF system.

Right now, I have a 2016 LML that claims my DEF level is empty even though it’s full. The tank and heater are about a year old and now the truck is barely out of warranty. No engine codes are being thrown just DIC showing empty DEF and is in limp mode.

I just replaced the DEF level and temperature sensor but now the DIC say service emersión system and is still in limp mode. Any ideas?

 

[roachmmflhyr]

After replacing the DEF level and temperature sensor yesterday it was still showing service emission system all day. I only drove it for 3 miles.

This morning I cranked it up and the message showed for 5 seconds and went away. No more limp mode either!