Code 1894 Now what?

[JimT]

(01-29-2020 )farmer70 Wrote:  So it can be inactive and everything will work ok? But if it is something really serious it will stay active? That code about the DEF unit was weird because it was full of DEF truck was bumped up to about 1100 rpm and out of nowhere the DEF light inside the DEF gauge comes on, the message center screen says DE RATE eminent. It was cold that night I wonder if it had something to do with that?

So when the engine computer (ECM) detects a problem it sets a fault code. As long as the problem is still being detected it is considered an "active" fault. When the problem is no longer detected it becomes an "inactive fault". The ECM keeps track of how many times these faults are triggered and a lot of information about the engine at the time of the fault. The dashboard display only shows "active" faults. But all faults, active or not, are stored in the ECM until manually cleared with a program such as Insite.

Everything the ECM knows about the engine and related systems is based on electrical signals from various sensors. So, when the ECM detects a fault there are 4 possible reasons:
1) the component being monitored is malfunctioning.
2) The sensor is malfunctioning .
3) the signal from the sensor to the ECM is being interrupted and/or changed.
4) The ECM is malfunctioning.

#1 and #2 are equally likely to be a problem and in some cases #1 and #2 are the same physical part. #3 would be the next likely candidate. And finally, in rare cases #4 could be the actual issue, although it's not likely.

So, in the case of the DEF level this would mean:
1) The fluid level in the tank has dropped too low.
2) The sensor that measures/reports the fluid level is no good.
3) There's a problem with the wires between the sensor and the ECM OR between the power supply and the sensor.
4) The ECM is malfunctioning.

You said the tank was full, so #1 can be eliminated. #2 would be you next suspect. However based on your descriptions of events, #3 should be investigated as a possible suspect.

In any case, the troubleshooting steps in insite/quickserve will help you to go through and investigate the issues in a logical fashion and they usually explain how to perform the different tests so no prior experience is required (just like most "techs" at the repair shops).

You're on the right track, you have the information you need to start troubleshooting the problem(s). Now it's up to you to either do the work yourself (always the best option) or find a competent shop that you can pay lots of money to do it for you (not the best option, but we all have limits to our abilities). If you do go with a shop doing the work, then take some time and find a GOOD shop that will actually do the proper troubleshooting BEFORE replacing any parts. Some shops will see that code for the turbo and tell you you need a new turbo. But your problem could be as simple as a corroded ground wire or a wire that has rubbed through and is shorting out occasionally.