P21AB Code.........

Was at the farm yesterday and the Check Engine Light came on on my 2012.

Returned home this morning I read the codes it read P21AB(CEL still on).
Check on the internet and it suggests a bad DEF level sensor or low on fluid.
I check the in dash status and it says DEF less than 1/2 full(doesn't say how much less).
I disconnect the code reader(didn't clear codes), start the engine and the Check Engine Light is off..WTH???
Went to the parts store and bought a jug of DEF and returned home. CEL still off.
Added DEF and CEL still off.
Hook up code reader and the P21AB code is still there so I clear it.

Will have to wait and see if it comes back. Hope it was just low on fluid. I have never gotten a CEL when low on DEF....its always been a DEF Low read out on the dash.

Anyone else ever seen this code?

I've never had a CEL, or that Code T, but... I don't like the dash read out that sez: "DEF level Okay". OKAY.. don't git it. I've never let it get low enough to tell me anything different.

Sooo.. Not a Fix but maybe a Hint ?.. I've always used the "Trip B" feature as a DEF level indicator. Every 2500 miles (or so) I just top off the DEF tank. Usually takes about 2 gallons (?), and reset trip B.

Also... My EDGE CTS has a DEF LEVEL option. From 100% it will go to 66%. When it does, I top it off and have compare the two.. the tank will take +/- 2 gallons.

Between the two, I feel I'm on top of the DEF thing. and maybe the CEL & Code ?

Joe

Now that I think about it I think I remember a Ford Tech telling me not to let the DEF get to low as it can cause problems with the sensors. Crap.