U040B code meaning
Invalid Data Received From Exhaust Gas Recirculation Control Module A
Network system Generic code U04xx codes Check engine light
What U040B means
U040B refers to an exhaust gas recirculation system driven by its own electronics on the bus, for example a smart EGR valve actuator that receives position targets and returns its measured position. The code is set when that unit's replies reach the engine controller but fail plausibility or protection checks, so the controller can no longer verify how much exhaust gas flows back. U040B appears in no public manufacturer document and in none of the bulletins indexed by NHTSA. GM's 2025 tables show how such checks work on other emission-related modules: counter, protection value and checksum, a fail ratio such as 8 of 18 samples, then a MIL. CARB requires EGR flow to be monitored, so the code counts as emission-relevant; expect EGR to be switched off, higher NOx and possibly less power. U010A is lost contact, U040C module B.
U040B 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 U040B
- Check engine light
- Reduced power or rough idle
- EGR flow codes stored alongside
Common causes of U040B
- PossibleElectronics or position sensor of the EGR actuator A delivering implausible values
- PossibleHeat-damaged connector or bus line at the EGR unit
- PossibleSoftware of engine controller and EGR module A out of step
- Less likelyEGR control module A internally faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
EGR module a
What each part of U040B means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 0B | The exact fault in that area. |
What to do next
- Note U040B 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 U040B
What does U040B mean?
U040B means "Invalid Data Received From Exhaust Gas Recirculation Control Module A". U040B refers to an exhaust gas recirculation system driven by its own electronics on the bus, for example a smart EGR valve actuator that receives position targets and returns its measured position. It is a generic code, so it means the same on every make.
Is it safe to drive with U040B?
Drive gently and only to a workshop. With U040B the car can go into limp mode (reduced power) to protect itself.
Will U040B fail an emissions test?
Yes, it can. U040B 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 U040B to fix?
Difficulty: hard. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will U040B clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.