U040F code meaning
Invalid Data Received From Reductant Control Module
Network system Generic code U04xx codes Check engine light
What U040F means
On a diesel with SCR, the reductant control module looks after the urea circuit, chiefly the pump, dosing and heater control, and reports pressure and status to the engine controller. U040F means its messages arrive but fail validation. GM's 2025 ECM tables check counter and checksum of the DEF information and dosing status frames, count 6 errors among 15 or 3 among 10 checks as a failure; the result is Type A with the MIL on trip one. Ford's 2023 diesel OBD summary groups U040F with the functional test of the reductant pump motor and sets it when the duty-cycle control signal of the pump motor controller leaves the 4 to 96 percent window, next to pump speed, voltage and temperature codes. Without trusted module data dosing is stopped, NOx rises and the inducement strategy may later limit speed. U010E is lost contact.
U040F at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyHard
- Typical labor0.5 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U040F
- Check engine light
- DEF/AdBlue warning with countdown to a speed limit
- Further SCR or reductant pump codes stored
Common causes of U040F
- PossiblePump motor controller in the reductant module reporting an invalid control signal
- PossibleCorroded connector or damaged bus line at the tank-mounted module
- PossibleSoftware of the reductant module or ECM out of step
- Less likelyReductant control module internally faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Reductant control module
What each part of U040F means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 0F | The exact fault in that area. |
What to do next
- Note U040F and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U040F
What does U040F mean?
U040F means "Invalid Data Received From Reductant Control Module". On a diesel with SCR, the reductant control module looks after the urea circuit, chiefly the pump, dosing and heater control, and reports pressure and status to the engine controller. It is a generic code, so it means the same on every make.
Is it safe to drive with U040F?
Drive gently and only to a workshop. With U040F the car can go into limp mode (reduced power) to protect itself.
Will U040F fail an emissions test?
Yes, it can. U040F is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is U040F to fix?
Difficulty: hard. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will U040F clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.