Photograph the warning
Record the full dash message, any countdown or derate status, and active codes. Follow the truck maker’s instructions; do not ignore a stop or speed-limiting warning.
Recall recent fluid handling
If known, note when DEF was added, the source and specification, and whether the issue followed a refill. Avoid introducing unverified fluid.
Do not erase the evidence
Clearing codes can remove useful diagnostic context without addressing the underlying issue. Share codes and operating history with the repair team.
Plan the next move carefully
A derate may limit safe travel. Ask a location whether it can evaluate the truck and whether mobile options may be available for your position.
Next step
For a specific truck, share its location, make and model, warning messages, and observed symptoms with a repair location. Availability and repair scope need direct confirmation.
Send a service inquiryThis educational guide is general information, not a diagnosis or substitute for safety procedures.